A case report of cavitary pneumonia caused by Legionella longbeachae in an immunocompetent patient

A case report of cavitary pneumonia caused by Legionella longbeachae in an immunocompetent patient | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report A case report of cavitary pneumonia caused by Legionella longbeachae in an immunocompetent patient Yixin Xu, Linfeng Cao, Xiaolong Ma This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9115058/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Background Legionella is a common causative pathogen of community-acquired pneumonia, but it encompasses multiple subtypes, with Legionella longbeachae ( L. longbeachae ) not being the most frequently encountered. Cavitary pneumonia is exceedingly rare in immunocompetent individuals, and cavitary pneumonia caused specifically by L. longbeachae in such patients is even more uncommon. Case presentation We describe a case of a 77-year-old female patient whose primary clinical manifestations were cough and myalgia. As the disease progressed, the patient gradually developed multiple cavities in the lower lobe of the right lung, exhibiting a chronic, protracted course. Metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid on two separate occasions indicated the presence of L. longbeachae. During hospitalization, she received sequential anti-infective therapy with levofloxacin, nemonoxacin, and omadacycline, ultimately improving and being discharged. Conclusions This represents the first definitively diagnosed case of cavitary pneumonia caused by L. longbeachae in a completely immunocompetent patient in the Chinese region. This case highlights the importance of maintaining clinical suspicion and confirms the value of applying mNGS in clinical infectious disease scenarios. The judicious use of quinolones or novel tetracycline derivatives demonstrates good efficacy against L. longbeachae. Legionella longbeachae cavity-type pneumonia Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Since its initial discovery in North America in 1977, Legionella has been recognized as a common cause of community-acquired pneumonia (CAP). Pneumonia is also the most prominent clinical manifestation of human Legionella infection( 1 , 2 ). The Legionella genus comprises 65 species, with Legionella pneumophila being the most significant, accounting for 80–90% of cases in Europe and the United States. Infections caused by Legionella longbeachae ( L.longbeachae ) represent only about 1% of cases, but it is the predominant species in Australia and New Zealand, accounting for 50–60% of cases( 3 , 4 ). In China, there is currently no data on the distribution of Legionella infection species, and reports of L.longbeachae infections are rare. The manifestations of Legionella infection vary widely, with disease severity ranging from mild febrile illness (Pontiac fever) to severe pneumonia( 5 ). Patients infected with Legionella are more likely to progress to severe pneumonia compared to those with other CAPs. The primary imaging findings include patchy and consolidating shadows in the lungs, often accompanied by impaired immune function, a history of long-term corticosteroid use, or other chronic diseases( 3 ). In immunocompromised patients, pulmonary cavitation is occasionally observed during the disease course, and there are very rare case reports of giant cavities occurring in immunocompetent patients with Legionella pneumonia( 6 ). In this study, we present a case of a patient in China definitively diagnosed with CAP caused by L.longbeachae . The patient exhibited an insidious onset, with cough as the primary clinical manifestation. The patient was immunocompetent and had no history of chronic diseases. However, imaging revealed a giant cavity in the lung, and there was delayed resolution of the pulmonary lesions following antibiotic therapy. This case highlights that, even in immunocompetent individuals with non-severe clinical symptoms, L.longbeachae should be considered as one of the potential pathogens in the management of patients with cavitary pneumonia. Case presentation The patient, a 78-year-old female, was admitted to a community health service center in Jiaxing, Zhejiang Province on October 20, 2025, due to "cough for 1 day". The patient reported being usually engaged in farming work and having a history of exposure to sewage water, with no history of entering air-conditioned environments. Prior to the onset of symptoms, she experienced mild muscle soreness but no discomfort such as fever or chills. Physical examination on admission revealed a heart rate of 102 beats per minute, with all other vital signs normal and no significant findings on the rest of the examination. Laboratory tests showed a white blood cell (WBC) count of 15.3×10⁹/L, neutrophil percentage of 97.1%, hypersensitive C-reactive protein (CRP) level of 212.7 mg/L, lactate dehydrogenase (LDH) level of 419 U/L, and erythrocyte sedimentation rate (ESR) of 130 mm/1h. The patient's serum sodium level is normal, at 140 mmol/L. A chest posteroanterior radiograph (DR) on October 20, 2025, showed partial atelectasis with patchy shadows in the middle and lower fields of the right lung (Fig. 1). A chest CT was performed on the next day, revealing extensive consolidation in the right lower lung lobe (Fig. 2). Due to equipment limitations at the local hospital, tests such as arterial blood gas analysis, β -D-glucan test, galactomannan antigen test, and respiratory tract throat swabs were not performed. The patient was admitted with a diagnosis of pulmonary infection, pleural effusion, and suspected right lung mass. She received a 4-day course of anti-infective therapy with levofloxacin combined with azlocillin. During hospitalization, she developed a fever, with a maximum temperature of 38.4°C, and her cough and sputum production showed no improvement. She was subsequently transferred to Pinghu First People's Hospital on October 23, 2025, for further inpatient treatment. Upon transfer, emergency arterial blood gas analysis and emergency brain natriuretic peptide (BNP) testing were performed. Results were as follows: pH was 7.49, partial pressure of carbon dioxide (PaCO₂) was 27 mmHg, partial pressure of oxygen (PaO₂) was 74 mmHg, lactate was 2.5 mmol/L; BNP was 36 pg/mL. On October 24, repeat blood tests, CRP, and PCT were conducted: red blood cell (RBC) count was 2.47×10 12 /L, hemoglobin was 74 g/L, WBC count was 6.6×10 9 /L, neutrophil percentage was 91.6%, platelet (PLT) count was 69×10 9 /L; CRP of 194.5 mg/L; PCT of 1.53 ng/mL; Serum sodium of 139 mmol/L. Treatment was initiated with meropenem combined with nemonoxacin for anti-infective therapy. On October 25, 2025, a thoracentesis and drainage procedure was performed. Routine analysis of the pleural fluid showed: Rivalta's test was positive; segmented neutrophils was 73%, lymphocytes was 24%, nucleated cell count was 6090/μL, mesothelial cells was 3%. Pleural fluid carcinoembryonic antigen (CEA) was 8.38 ng/mL, and alpha-fetoprotein (AFP) was 0.91 ng/mL. Pleural fluid acid-fast bacillus smear and bacterial culture both returned negative results. Cytological examination of the pleural fluid did not reveal definitive malignant tumor cells. Inflammatory cells and scattered mesothelial cells were observed. On October 27, 2025, bronchoscopy with bronchoalveolar lavage (BAL) was performed, revealing mucosal edema at the orifice of the dorsal segment of the right lower lobe. On October 28, metagenomic next-generation sequencing (mNGS) results of the BAL fluid were reported: L. longbeachae 10,864 reads, Human herpesvirus 1 (HHV-1) 445 reads. The antibiotic regimen was changed on the same day to doxycycline combined with nemonoxacin. On October 31, a follow-up chest CT showed the presence of multiple cavities (Fig. 3). Therefore, the anti-infective regimen was adjusted again to ceftazidime-avibactam in combination with nemonoxacin malate. After one week of treatment with the above regimen, a repeat chest CT was performed, which showed progression of the cavities (Fig. 4). On November 08, 2025, follow-up blood tests were performed: WBC count was 10.0×10 9 /L, NEU count was 8.56×10 9 /L, RBC count was 2.73×10 12 /L, hemoglobin was 82 g/L; CRP was 26.4 mg/L. These results showed improvement compared to previous tests. The patient was discharged on November 10, 2025, and continued oral anti-infective therapy with faropenem combined with nemonoxacin. After discharge, the patient continued to experience cough with scant sputum production, but had no discomfort such as fever or muscle aches. On November 28, 2025, she sought medical attention at The First Hospital of Jiaxing and was subsequently hospitalized. Blood tests revealed: WBC count was 11.82×10⁹/L, NEU count was 8.2×10⁹/L, RBC count was 3.58×10¹²/L, hemoglobin was 108 g/L; CRP was 11.7 mg/L; PCT was 0.05 ng/mL. Tests for LDH, creatine kinase (CK), creatine kinase-MB isoenzyme (CK-MB), β -D-glucan, and galactomannan antigen all returned negative results. A follow-up chest CT indicated that the pulmonary cavities had progressed compared to the previous examination (Fig. 5). Upon admission, an anti-infective regimen of omadacycline combined with levofloxacin was initiated. A CT pulmonary angiography (CTPA) performed on December 5, 2025, indicated a reduction in the size of the cavity in the right lower lobe (Fig. 6). A repeat chest CT on December 13, 2025, showed no significant change in the cavities (Fig. 7). To rule out other possible pathologies, a repeat BAL along with endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) was performed on December 15, 2025. The BAL fluid analysis showed a nucleated cell count of 217/μL and RBC count of 8000/μL; tests for galactomannan antigen and cryptococcal capsular antigen were both negative. The pathology report received on December 16, 2025, indicated chronic inflammation of the bronchial mucosa and lung tissue, active with erosion and necrosis. mNGS of the BAL fluid reported on December 17, 2025, detected L. longbeachae (1,750 reads). The read count had decreased compared to the previous test, with no evidence of other pathogenic infections. Follow-up blood tests after treatment showed: WBC count was 11.91×10⁹/L, NEU count was 8.61×10⁹/L, RBC count was 3.35×10¹²/L, hemoglobin was 100 g/L; CRP was 4.9 mg/L. The patient was discharged on December 19, 2025, and continued oral anti-infective therapy with doxycycline, levofloxacin, and azithromycin post-discharge. Fig. 8 shows the changes in some key markers during the patient's three hospitalizations. Discussion In recent years, the incidence of Legionella pneumonia has been steadily increasing worldwide. Due to its often non-specific symptoms and signs, Legionella is frequently overlooked in the diagnosis of CAP( 7 , 8 ). In Europe and the United States, Legionella pneumonia is primarily contracted through exposure to Legionella pneumophila in contaminated water( 9 , 10 ). In contrast, L.longbeachae is more commonly found in soil, often associated with exposure to commercial potting soil or household compost( 11 ). Infections caused by L.longbeachae are prevalent in Australia and New Zealand, with occasional reports in Europe, North America, and Japan( 10 , 12 ). Currently, L.longbeachae infections are exceptionally rare in China, with only one case reported in Nanchang, Jiangxi in 2020 and another in Haikou, Hainan in 2021( 13 , 14 ). This patient had exposure to both contaminated water and potting soil, placing them at high risk for Legionella infection. Based on the BAL results, the source of infection is more likely to have originated from soil exposure. Pneumonia is the primary clinical manifestation of Legionella infection, with most literature reporting severe cases of Legionella pneumonia. According to international data, over 20% of patients with Legionella infection require ICU admission, with an overall mortality rate ranging from 4% to 18%( 15 ). Symptoms of Legionella pneumonia include fever, cough with sputum, dyspnea, myalgia or arthralgia, diarrhea, and nausea or vomiting. Common laboratory findings include elevated muscle enzyme levels, increased inflammatory markers such as CRP and PCT, and hyponatremia, which is one of the most characteristic features and is often difficult to correct( 1 , 16 , 17 ). Whether caused by Legionella pneumophila , L.longbeachae , or other Legionella species, the symptoms of infection are quite similar. It is currently not possible to differentiate between them based solely on clinical presentation, nor can Legionella be distinguished from other pathogens of CAP based on clinical features alone( 18 ). In this case, the patient’s clinical presentation was atypical, with cough as the main symptom, and fever only occurring during the first hospitalization. However, upon admission, the patient’s WBC count, muscle enzyme levels, and inflammatory markers were significantly elevated, which is consistent with findings reported in most case studies. On chest X-rays or CT scans, patients with Legionella pneumonia typically present with patchy infiltrates or consolidation. Other common imaging features include air bronchogram signs and halo signs, and some patients may exhibit pleural effusion( 1 , 17 , 19 ). In patients receiving corticosteroid therapy or those with immunosuppression, rounded nodular cavities may occur( 19 – 21 ). Overall, cavitation is relatively uncommon and is particularly rare in immunocompetent individuals. In 2024, a hospital in Shandong, China, reported a case of pulmonary cavitation in an immunocompetent patient following Legionella infection, and a similar case was documented in Europe in 2019. However, mNGS identified Legionella pneumophila as the causative pathogen in both instances( 6 ). To date, there have been no reported cases of pulmonary cavitation caused by L.longbeachae . In the present case, two BAL examinations were performed, and mNGS testing of both samples indicated L.longbeachae , confirming the etiological diagnosis. Furthermore, this patient had no evidence of immunosuppression or a history of long-term corticosteroid use. This suggests that L.longbeachae should also be considered as a possible pathogen when pulmonary imaging reveals cavitary lesions. Etiological detection is a critical step in confirming the diagnosis of Legionella infection. Common detection methods include culture isolation, serological testing, urinary antigen testing (UAT), polymerase chain reaction (PCR), and mNGS( 19 ). Conventional culture methods are time-consuming and often lack sensitivity for Legionella species( 22 , 23 ). Urinary antigen testing can only detect Legionella pneumophila serogroup 1 and is ineffective for identifying other Legionella species( 14 , 24 ). PCR offers higher sensitivity than culture but cannot differentiate whether the detected fragments are from viable organisms, potentially leading to false-positive results( 23 , 25 ). Compared to traditional culture or PCR, mNGS provides distinct advantages in cases involving difficult-to-culture pathogens. It enables the analysis of all microorganisms in a single sample, allowing simultaneous identification of co-infecting pathogens and saving significant time( 19 , 26 , 27 ). Typically, the diagnosis of L.longbeachae relies more heavily on culture, PCR, and mNGS. The two previously reported cases of L.longbeachae in China, as well as the present case, were all confirmed through NGS. In this patient, two bronchoscopic examinations and NGS analysis of the lavage fluid provided a clear etiological diagnosis, with a significant decrease in read counts observed following antimicrobial therapy. Persistently positive PCR results may be associated with conditions such as lung abscess or slowly resolving Legionella infections( 3 ). Fluoroquinolones or macrolide antibiotics are the first-line treatment for Legionella pneumonia( 7 , 28 , 29 ). Initiating anti-infective therapy early can prevent symptom progression and reduce ICU admission rates( 30 ). Most studies indicate no significant difference in efficacy between these two antibiotic classes. However, fluoroquinolones may be superior to macrolides when the patient progresses to severe pneumonia( 3 , 7 , 31 ). The optimal duration of antibiotic therapy for Legionella pneumonia has not been clearly defined. For patients with mild symptoms, a total treatment duration of 3–7 days is recommended, continuing until the patient is clinically stable and has been afebrile for at least 48 hours( 15 ). For immunocompromised hosts, a 21-day course of levofloxacin or a 10-day course of azithromycin is generally advised( 32 , 33 ). Recently, several case reports have documented successful treatment of Legionella pneumonia patients with omadacycline( 34 , 35 ). In this case, the patient received sequential anti-infective therapy with levofloxacin, nemonoxacin, and omadacycline, followed by oral doxycycline, levofloxacin, and azithromycin after discharge. The clinical course was prolonged with a very long total treatment duration, and the lung lesions showed chronic cavitary changes, which differs from the typical rapid progression of Legionella pneumonia. The significant decrease in mNGS read counts from the BAL fluid after treatment suggests that the anti-infective therapy was effective. Although corticosteroid use in severe pneumonia can improve patient outcomes and reduce mortality, a history of steroid use is a major risk factor for Legionella pneumonia. Administering corticosteroids to patients with Legionella infection may potentially lead to disease progression or relapse, necessitating extreme caution in their application( 3 ). Discussion and Conclusion To the best of our knowledge, this is the first reported case of cavitary pneumonia definitively diagnosed as L.longbeachae infection. Typically, Legionella pneumonia is characterized by rapid progression and severe clinical presentation. However, this case suggests that it can also manifest with chronic, protracted changes. The possibility of L.longbeachae infection should be considered even in immunocompetent individuals with CAP. mNGS may be the most effective tool for diagnosing L.longbeachae infection. Abbreviations CAP community-acquired pneumonia L.longbeachae Legionella longbeachae WBC white blood cell CRP C-reactive protein LDH lactate dehydrogenase DR posteroanterior radiograph BNP brain natriuretic peptide PaCO₂ partial pressure of carbon dioxide PaO₂ partial pressure of oxygen RBC red blood cell PLT platelet CEA carcinoembryonic antigen AFP alpha-fetoprotein BAL bronchoalveolar lavage mNGS metagenomic next-generation sequencing HHV-1 Human herpesvirus 1 CK creatine kinase CK-MB creatine kinase-MB isoenzyme CTPA CT pulmonary angiography EBUS-TBNA endobronchial ultrasound-guided transbronchial needle aspiration UAT urinary antigen testing PCR polymerase chain reaction Declarations Ethics approval and consent to participate The research has complied with the Declaration of Helsinki and has been approved by Ethics Committee in Clinical Research of The First Hosptial of Jiaxing, China. Informed consent to participate was obtained from all the participants. Consent to publish declaration Written informed consent was obtained from the patient for publication. Competing interests The authors declare no competing interests. Availability of data and materials The data and images presented in this article are available from the corresponding author upon request. Funding None. Authors' contributions Y.X. and L.C.: collected data, wrote the main manuscript text. X.M.: critically reviewed and approved the final version of manuscript. Acknowledgements We are appreciative of patient and her representative for agreement to this publication. References Cunha BA, Burillo A, Bouza E. Legionnaires' disease. Lancet (London, England). 2016;387(10016):376-85. Chahin A, Opal SM. Severe Pneumonia Caused by Legionella pneumophila: Differential Diagnosis and Therapeutic Considerations. Infectious disease clinics of North America. 2017;31(1):111-21. Rello J, Allam C, Ruiz-Spinelli A, Jarraud S. Severe Legionnaires' disease. 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Omadacycline successfully treated severe Legionella pneumonia after moxifloxacin treatment failure: Case series. Frontiers in pharmacology. 2025;16:1559857. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 17 May, 2026 Reviewers agreed at journal 09 May, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers invited by journal 23 Apr, 2026 Editor invited by journal 01 Apr, 2026 Editor assigned by journal 25 Mar, 2026 Submission checks completed at journal 25 Mar, 2026 First submitted to journal 25 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9115058","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":633686029,"identity":"50f03034-7bb2-4e93-9ac3-1560bd43f866","order_by":0,"name":"Yixin Xu","email":"","orcid":"","institution":"The First Hospital of Jiaxing in Zhejiang Province, Affiliated Hospital of Jiaxing University","correspondingAuthor":false,"prefix":"","firstName":"Yixin","middleName":"","lastName":"Xu","suffix":""},{"id":633686031,"identity":"9e0fa76c-faca-4e0b-a877-f06865e6b5a0","order_by":1,"name":"Linfeng Cao","email":"","orcid":"","institution":"The First Hospital of Jiaxing in Zhejiang Province, Affiliated Hospital of Jiaxing University","correspondingAuthor":false,"prefix":"","firstName":"Linfeng","middleName":"","lastName":"Cao","suffix":""},{"id":633686034,"identity":"360dae07-93be-45e1-a1b6-f1bbf125a3ec","order_by":2,"name":"Xiaolong Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDUlEQVRIie2QP0vEMBiHUwqdUju4vHJS/AJCSqF3Qr+JS8pBJt07HNJD6C2Caz+EgyA4pwScAlk7xsXpht7moph6gzqkdhTMM+Ql8Ht4/yDkcPxROEILU7y17kvAke8LPUEBU3yRNHIRH20CRiY0GpSAHYZ1mRKFT2Ase7qRCX8tIZ5Hd5nXBFA8CIwIWuXnNiWTjLY3EtKzZpvpHkPxKEKu0RO7rGwKX3Ie1lDcd3KeNDAoB5R4lbAr6rlq3/ZKNsPEDHZt3lGlW3Lx2UXVbIYppMT/VXmh4tjsQrrhyBxiEObIdGwXdZHutmUeE9Wu9e79Cke3Quh+lVuVL4B++1BL6CcRnxRzOByOf8gHl5VjfslrbPIAAAAASUVORK5CYII=","orcid":"","institution":"The First Hospital of Jiaxing in Zhejiang Province, Affiliated Hospital of Jiaxing University","correspondingAuthor":true,"prefix":"","firstName":"Xiaolong","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2026-03-13 13:08:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9115058/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9115058/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108820244,"identity":"99ac7fc1-74f2-45e1-b8d9-ed194545f5a1","added_by":"auto","created_at":"2026-05-08 16:40:38","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":162733,"visible":true,"origin":"","legend":"\u003cp\u003eThe patient's first chest imaging examination after onset of illness (October 20, 2025). Extensive consolidation is visible in the right lower lung.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/8ceec969812b2c91ad5ed82f.png"},{"id":108819788,"identity":"2669c998-6c90-4e11-9015-5f26066cb962","added_by":"auto","created_at":"2026-05-08 16:38:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":375301,"visible":true,"origin":"","legend":"\u003cp\u003eChest CT on October 21, 2025: A high-density consolidation is seen in the right lower lobe, containing a few aerated bronchi within it. The tracheal and bronchial openings are patent, with no signs of stenosis. A suspicious soft tissue nodule is noted adjacent to the right hilum.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/82ffba5d6b8a67d930c51488.png"},{"id":108820246,"identity":"41b26c30-0ce9-4b3a-9443-703c4ecdb377","added_by":"auto","created_at":"2026-05-08 16:40:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":273219,"visible":true,"origin":"","legend":"\u003cp\u003eChest CT on October 31, 2025: Multiple patchy high-density opacities with ill-defined margins are seen in both lungs, some showing consolidation and air bronchogram signs. These are most prominent in the right lower lobe, with cavitation noted within the lesions.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/3a9f36b23de2afc401746c76.png"},{"id":108819756,"identity":"5dc5c880-2215-4bf6-b7c6-f5ef730babf6","added_by":"auto","created_at":"2026-05-08 16:38:43","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":246018,"visible":true,"origin":"","legend":"\u003cp\u003eChest CT on November 06, 2025: Multiple inflammatory opacities are still visible in both lungs. The cavities have enlarged compared to the previous scan, while the peripheral exudative lesions show slight improvement with some absorption.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/cc206141d9e61e4367147c3a.png"},{"id":108820116,"identity":"94deae7a-4b00-487a-8620-da28005c8bd8","added_by":"auto","created_at":"2026-05-08 16:40:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":269051,"visible":true,"origin":"","legend":"\u003cp\u003eChest CT on November 28, 2025: Partial consolidation with cavity formation is observed in the right lower lobe. The inflammatory changes in both lungs show improvement with absorption compared to the previous scan. However, the cavities in the right lower lobe have enlarged and increased in number compared to prior imaging.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/e73d4bbcc2feb015c5d44f9b.png"},{"id":108819799,"identity":"ea29980b-43da-4d8e-a97f-41734f694913","added_by":"auto","created_at":"2026-05-08 16:38:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":268472,"visible":true,"origin":"","legend":"\u003cp\u003eCTPA performed on December 5, 2025: Partial consolidation with cavity formation is seen in the right lower lobe. The cavity in the right lower lobe has decreased in size compared to the CT scan dated November 28, 2025.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/b739fe1fb3888cc61e37f5a1.png"},{"id":108820060,"identity":"ccb18d1b-cf53-470b-89ae-bc62b505db51","added_by":"auto","created_at":"2026-05-08 16:39:57","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":285291,"visible":true,"origin":"","legend":"\u003cp\u003eChest CT on December 13, 2025: Consolidation with cavity formation is observed in the right lower lobe, showing no significant change compared to the previous scan.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/4870b08691c24c9287a5b606.png"},{"id":108819868,"identity":"a56de221-706f-4ff2-aebb-bf3125c866b6","added_by":"auto","created_at":"2026-05-08 16:39:10","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":392607,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in key indicators during the patient's three hospitalizations: At the early stage of infection, the WBC count, CRP, and PCT were significantly elevated. Due to the severity of the infection, the PLT count was low. As antibiotic therapy effectively targeted the pathogen, the PLT count recovered, and all inflammatory markers showed significant improvement. Although the white blood cell count fluctuated, it overall exhibited a downward trend.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/0ec689cea26e69f92e702758.png"},{"id":109068017,"identity":"78bf0902-54a1-4ff4-bf9f-057663fb4b4c","added_by":"auto","created_at":"2026-05-12 10:02:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2510138,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9115058/v1/84a913f5-8f1d-4caf-a1cc-4fecd29b3984.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A case report of cavitary pneumonia caused by Legionella longbeachae in an immunocompetent patient","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSince its initial discovery in North America in 1977, \u003cem\u003eLegionella\u003c/em\u003e has been recognized as a common cause of community-acquired pneumonia (CAP). Pneumonia is also the most prominent clinical manifestation of human \u003cem\u003eLegionella\u003c/em\u003e infection(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). The Legionella genus comprises 65 species, with \u003cem\u003eLegionella pneumophila\u003c/em\u003e being the most significant, accounting for 80\u0026ndash;90% of cases in Europe and the United States. Infections caused by \u003cem\u003eLegionella longbeachae\u003c/em\u003e (\u003cem\u003eL.longbeachae\u003c/em\u003e) represent only about 1% of cases, but it is the predominant species in Australia and New Zealand, accounting for 50\u0026ndash;60% of cases(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). In China, there is currently no data on the distribution of \u003cem\u003eLegionella\u003c/em\u003e infection species, and reports of \u003cem\u003eL.longbeachae\u003c/em\u003e infections are rare. The manifestations of \u003cem\u003eLegionella\u003c/em\u003e infection vary widely, with disease severity ranging from mild febrile illness (Pontiac fever) to severe pneumonia(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Patients infected with \u003cem\u003eLegionella\u003c/em\u003e are more likely to progress to severe pneumonia compared to those with other CAPs. The primary imaging findings include patchy and consolidating shadows in the lungs, often accompanied by impaired immune function, a history of long-term corticosteroid use, or other chronic diseases(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). In immunocompromised patients, pulmonary cavitation is occasionally observed during the disease course, and there are very rare case reports of giant cavities occurring in immunocompetent patients with \u003cem\u003eLegionella\u003c/em\u003e pneumonia(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this study, we present a case of a patient in China definitively diagnosed with CAP caused by \u003cem\u003eL.longbeachae\u003c/em\u003e. The patient exhibited an insidious onset, with cough as the primary clinical manifestation. The patient was immunocompetent and had no history of chronic diseases. However, imaging revealed a giant cavity in the lung, and there was delayed resolution of the pulmonary lesions following antibiotic therapy. This case highlights that, even in immunocompetent individuals with non-severe clinical symptoms, \u003cem\u003eL.longbeachae\u003c/em\u003e should be considered as one of the potential pathogens in the management of patients with cavitary pneumonia.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eThe patient, a 78-year-old female, was admitted to a community health service center in Jiaxing, Zhejiang Province on October 20, 2025, due to \"cough for 1 day\". The patient reported being usually engaged in farming work and having a history of exposure to sewage water, with no history of entering air-conditioned environments. Prior to the onset of symptoms, she experienced mild muscle soreness but no discomfort such as fever or chills. Physical examination on admission revealed a heart rate of 102 beats per minute, with all other vital signs normal and no significant findings on the rest of the examination. Laboratory tests showed a white blood cell (WBC) count of 15.3×10⁹/L, neutrophil percentage of 97.1%, hypersensitive C-reactive protein (CRP) level of 212.7 mg/L, lactate dehydrogenase (LDH) level of 419 U/L, and erythrocyte sedimentation rate (ESR) of 130 mm/1h. The patient's serum sodium level is normal, at 140 mmol/L. A chest posteroanterior radiograph (DR) on October 20, 2025, showed partial atelectasis with patchy shadows in the middle and lower fields of the right lung (Fig. 1). A chest CT was performed on the next day, revealing extensive consolidation in the right lower lung lobe (Fig. 2). Due to equipment limitations at the local hospital, tests such as arterial blood gas analysis, \u003cem\u003eβ\u003c/em\u003e-D-glucan test, galactomannan antigen test, and respiratory tract throat swabs were not performed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe patient was admitted with a diagnosis of pulmonary infection, pleural effusion, and suspected right lung mass. She received a 4-day course of anti-infective therapy with levofloxacin combined with azlocillin. During hospitalization, she developed a fever, with a maximum temperature of 38.4°C, and her cough and sputum production showed no improvement. She was subsequently transferred to Pinghu First People's Hospital on October 23, 2025, for further inpatient treatment.\u003c/p\u003e\n\u003cp\u003eUpon transfer, emergency arterial blood gas analysis and emergency brain natriuretic peptide (BNP) testing were performed. Results were as follows: pH was 7.49, partial pressure of carbon dioxide (PaCO₂) was 27 mmHg, partial pressure of oxygen (PaO₂) was 74 mmHg, lactate was 2.5 mmol/L; BNP was 36 pg/mL. On October 24, repeat blood tests, CRP, and PCT were conducted: red blood cell (RBC)\u0026nbsp;count was\u0026nbsp;2.47×10\u003csup\u003e12\u003c/sup\u003e/L, hemoglobin was\u0026nbsp;74\u0026nbsp;g/L,\u0026nbsp;WBC\u0026nbsp;count was\u0026nbsp;6.6×10\u003csup\u003e9\u003c/sup\u003e/L, neutrophil percentage was\u0026nbsp;91.6%, platelet\u0026nbsp;(PLT)\u0026nbsp;count was\u0026nbsp;69×10\u003csup\u003e9\u003c/sup\u003e/L; CRP\u0026nbsp;of\u0026nbsp;194.5 mg/L; PCT\u0026nbsp;of\u0026nbsp;1.53 ng/mL; Serum sodium\u0026nbsp;of\u0026nbsp;139 mmol/L. Treatment was initiated with meropenem combined with nemonoxacin for anti-infective therapy.\u003c/p\u003e\n\u003cp\u003eOn October 25, 2025, a thoracentesis and drainage procedure was performed. Routine analysis of the pleural fluid showed: Rivalta's test was positive; segmented neutrophils was 73%, lymphocytes was 24%, nucleated cell count was 6090/μL, mesothelial cells was 3%. Pleural fluid carcinoembryonic antigen (CEA) was 8.38 ng/mL, and alpha-fetoprotein (AFP) was 0.91 ng/mL. Pleural fluid acid-fast bacillus smear and bacterial culture both returned negative results. Cytological examination of the pleural fluid did not reveal definitive malignant tumor cells. Inflammatory cells and scattered mesothelial cells were observed. On October 27, 2025, bronchoscopy with bronchoalveolar lavage (BAL) was performed, revealing mucosal edema at the orifice of the dorsal segment of the right lower lobe. On October 28, metagenomic next-generation sequencing (mNGS) results of the BAL fluid were reported:\u0026nbsp;\u003cem\u003eL.\u003c/em\u003e\u003cem\u003elongbeachae\u003c/em\u003e 10,864 reads, \u003cem\u003eHuman herpesvirus 1\u003c/em\u003e (HHV-1) 445 reads. The antibiotic regimen was changed on the same day to doxycycline combined with nemonoxacin.\u0026nbsp;On October 31, a follow-up chest CT showed the presence of multiple cavities\u0026nbsp;(Fig. 3). Therefore, the anti-infective regimen was adjusted again to ceftazidime-avibactam in combination with nemonoxacin malate.\u003c/p\u003e\n\u003cp\u003eAfter one week of treatment with the above regimen, a repeat chest CT was performed, which showed progression of the cavities (Fig. 4). On November 08, 2025, follow-up blood tests were performed: WBC count was 10.0×10\u003csup\u003e9\u003c/sup\u003e/L, NEU count was 8.56×10\u003csup\u003e9\u003c/sup\u003e/L, RBC count was 2.73×10\u003csup\u003e12\u003c/sup\u003e/L, hemoglobin was 82 g/L; CRP was 26.4 mg/L. These results showed improvement compared to previous tests. The patient was discharged on November 10, 2025, and continued oral anti-infective therapy with faropenem combined with nemonoxacin.\u003c/p\u003e\n\u003cp\u003eAfter discharge, the patient continued to experience cough with scant sputum production, but had no discomfort such as fever or muscle aches. On November 28, 2025, she sought medical attention at The First Hospital of Jiaxing and was subsequently hospitalized. Blood tests revealed: WBC count was 11.82×10⁹/L, NEU count was 8.2×10⁹/L, RBC count was 3.58×10¹²/L, hemoglobin was 108 g/L; CRP was 11.7 mg/L; PCT was 0.05 ng/mL. Tests for LDH, creatine kinase (CK), creatine kinase-MB isoenzyme (CK-MB), \u003cem\u003eβ\u003c/em\u003e-D-glucan, and galactomannan antigen all returned negative results. A follow-up chest CT indicated that the pulmonary cavities had progressed compared to the previous examination (Fig. 5).\u003c/p\u003e\n\u003cp\u003eUpon admission, an anti-infective regimen of omadacycline combined with levofloxacin was initiated. A CT pulmonary angiography (CTPA) performed on December 5, 2025, indicated a reduction in the size of the cavity in the right lower lobe (Fig. 6). A repeat chest CT on December 13, 2025, showed no significant change in the cavities (Fig. 7). To rule out other possible pathologies, a repeat BAL along with endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) was performed on December 15, 2025. The BAL fluid analysis showed a nucleated cell count of 217/μL and RBC count of 8000/μL; tests for galactomannan antigen and cryptococcal capsular antigen were both negative. The pathology report received on December 16, 2025, indicated chronic inflammation of the bronchial mucosa and lung tissue, active with erosion and necrosis. mNGS of the BAL fluid reported on December 17, 2025, detected\u0026nbsp;\u003cem\u003eL.\u003c/em\u003e\u003cem\u003elongbeachae\u003c/em\u003e (1,750 reads). The read count had decreased compared to the previous test, with no evidence of other pathogenic infections. Follow-up blood tests after treatment showed:\u0026nbsp;WBC\u0026nbsp;count was\u0026nbsp;11.91×10⁹/L,\u0026nbsp;NEU\u0026nbsp;count was\u0026nbsp;8.61×10⁹/L,\u0026nbsp;RBC\u0026nbsp;count was\u0026nbsp;3.35×10¹²/L, hemoglobin was\u0026nbsp;100 g/L;\u0026nbsp;CRP\u0026nbsp;was\u0026nbsp;4.9 mg/L. The patient was discharged on December 19, 2025, and continued oral anti-infective therapy with doxycycline, levofloxacin, and azithromycin post-discharge. Fig.\u0026nbsp;8 shows the changes in some key markers during the patient's three hospitalizations.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn recent years, the incidence of \u003cem\u003eLegionella\u003c/em\u003e pneumonia has been steadily increasing worldwide. Due to its often non-specific symptoms and signs, \u003cem\u003eLegionella\u003c/em\u003e is frequently overlooked in the diagnosis of CAP(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). In Europe and the United States, \u003cem\u003eLegionella\u003c/em\u003e pneumonia is primarily contracted through exposure to \u003cem\u003eLegionella pneumophila\u003c/em\u003e in contaminated water(\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). In contrast, \u003cem\u003eL.longbeachae\u003c/em\u003e is more commonly found in soil, often associated with exposure to commercial potting soil or household compost(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Infections caused by \u003cem\u003eL.longbeachae\u003c/em\u003e are prevalent in Australia and New Zealand, with occasional reports in Europe, North America, and Japan(\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Currently, \u003cem\u003eL.longbeachae\u003c/em\u003e infections are exceptionally rare in China, with only one case reported in Nanchang, Jiangxi in 2020 and another in Haikou, Hainan in 2021(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). This patient had exposure to both contaminated water and potting soil, placing them at high risk for \u003cem\u003eLegionella\u003c/em\u003e infection. Based on the BAL results, the source of infection is more likely to have originated from soil exposure.\u003c/p\u003e \u003cp\u003ePneumonia is the primary clinical manifestation of \u003cem\u003eLegionella\u003c/em\u003e infection, with most literature reporting severe cases of \u003cem\u003eLegionella\u003c/em\u003e pneumonia. According to international data, over 20% of patients with \u003cem\u003eLegionella\u003c/em\u003e infection require ICU admission, with an overall mortality rate ranging from 4% to 18%(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Symptoms of \u003cem\u003eLegionella\u003c/em\u003e pneumonia include fever, cough with sputum, dyspnea, myalgia or arthralgia, diarrhea, and nausea or vomiting. Common laboratory findings include elevated muscle enzyme levels, increased inflammatory markers such as CRP and PCT, and hyponatremia, which is one of the most characteristic features and is often difficult to correct(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Whether caused by \u003cem\u003eLegionella pneumophila\u003c/em\u003e, \u003cem\u003eL.longbeachae\u003c/em\u003e, or other \u003cem\u003eLegionella\u003c/em\u003e species, the symptoms of infection are quite similar. It is currently not possible to differentiate between them based solely on clinical presentation, nor can \u003cem\u003eLegionella\u003c/em\u003e be distinguished from other pathogens of CAP based on clinical features alone(\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). In this case, the patient\u0026rsquo;s clinical presentation was atypical, with cough as the main symptom, and fever only occurring during the first hospitalization. However, upon admission, the patient\u0026rsquo;s WBC count, muscle enzyme levels, and inflammatory markers were significantly elevated, which is consistent with findings reported in most case studies. On chest X-rays or CT scans, patients with \u003cem\u003eLegionella\u003c/em\u003e pneumonia typically present with patchy infiltrates or consolidation. Other common imaging features include air bronchogram signs and halo signs, and some patients may exhibit pleural effusion(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). In patients receiving corticosteroid therapy or those with immunosuppression, rounded nodular cavities may occur(\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). Overall, cavitation is relatively uncommon and is particularly rare in immunocompetent individuals. In 2024, a hospital in Shandong, China, reported a case of pulmonary cavitation in an immunocompetent patient following \u003cem\u003eLegionella\u003c/em\u003e infection, and a similar case was documented in Europe in 2019. However, mNGS identified \u003cem\u003eLegionella pneumophila\u003c/em\u003e as the causative pathogen in both instances(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). To date, there have been no reported cases of pulmonary cavitation caused by \u003cem\u003eL.longbeachae\u003c/em\u003e. In the present case, two BAL examinations were performed, and mNGS testing of both samples indicated \u003cem\u003eL.longbeachae\u003c/em\u003e, confirming the etiological diagnosis. Furthermore, this patient had no evidence of immunosuppression or a history of long-term corticosteroid use. This suggests that \u003cem\u003eL.longbeachae\u003c/em\u003e should also be considered as a possible pathogen when pulmonary imaging reveals cavitary lesions.\u003c/p\u003e \u003cp\u003eEtiological detection is a critical step in confirming the diagnosis of \u003cem\u003eLegionella\u003c/em\u003e infection. Common detection methods include culture isolation, serological testing, urinary antigen testing (UAT), polymerase chain reaction (PCR), and mNGS(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). Conventional culture methods are time-consuming and often lack sensitivity for \u003cem\u003eLegionella\u003c/em\u003e species(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). Urinary antigen testing can only detect \u003cem\u003eLegionella pneumophila\u003c/em\u003e serogroup 1 and is ineffective for identifying other \u003cem\u003eLegionella\u003c/em\u003e species(\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). PCR offers higher sensitivity than culture but cannot differentiate whether the detected fragments are from viable organisms, potentially leading to false-positive results(\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). Compared to traditional culture or PCR, mNGS provides distinct advantages in cases involving difficult-to-culture pathogens. It enables the analysis of all microorganisms in a single sample, allowing simultaneous identification of co-infecting pathogens and saving significant time(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). Typically, the diagnosis of \u003cem\u003eL.longbeachae\u003c/em\u003e relies more heavily on culture, PCR, and mNGS. The two previously reported cases of \u003cem\u003eL.longbeachae\u003c/em\u003e in China, as well as the present case, were all confirmed through NGS. In this patient, two bronchoscopic examinations and NGS analysis of the lavage fluid provided a clear etiological diagnosis, with a significant decrease in read counts observed following antimicrobial therapy. Persistently positive PCR results may be associated with conditions such as lung abscess or slowly resolving \u003cem\u003eLegionella\u003c/em\u003e infections(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFluoroquinolones or macrolide antibiotics are the first-line treatment for \u003cem\u003eLegionella\u003c/em\u003e pneumonia(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). Initiating anti-infective therapy early can prevent symptom progression and reduce ICU admission rates(\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e). Most studies indicate no significant difference in efficacy between these two antibiotic classes. However, fluoroquinolones may be superior to macrolides when the patient progresses to severe pneumonia(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e). The optimal duration of antibiotic therapy for \u003cem\u003eLegionella\u003c/em\u003e pneumonia has not been clearly defined. For patients with mild symptoms, a total treatment duration of 3\u0026ndash;7 days is recommended, continuing until the patient is clinically stable and has been afebrile for at least 48 hours(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). For immunocompromised hosts, a 21-day course of levofloxacin or a 10-day course of azithromycin is generally advised(\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e). Recently, several case reports have documented successful treatment of \u003cem\u003eLegionella\u003c/em\u003e pneumonia patients with omadacycline(\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). In this case, the patient received sequential anti-infective therapy with levofloxacin, nemonoxacin, and omadacycline, followed by oral doxycycline, levofloxacin, and azithromycin after discharge. The clinical course was prolonged with a very long total treatment duration, and the lung lesions showed chronic cavitary changes, which differs from the typical rapid progression of \u003cem\u003eLegionella\u003c/em\u003e pneumonia. The significant decrease in mNGS read counts from the BAL fluid after treatment suggests that the anti-infective therapy was effective. Although corticosteroid use in severe pneumonia can improve patient outcomes and reduce mortality, a history of steroid use is a major risk factor for \u003cem\u003eLegionella\u003c/em\u003e pneumonia. Administering corticosteroids to patients with \u003cem\u003eLegionella\u003c/em\u003e infection may potentially lead to disease progression or relapse, necessitating extreme caution in their application(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion and Conclusion","content":"\u003cp\u003eTo the best of our knowledge, this is the first reported case of cavitary pneumonia definitively diagnosed as \u003cem\u003eL.longbeachae\u003c/em\u003e infection. Typically, \u003cem\u003eLegionella\u003c/em\u003e pneumonia is characterized by rapid progression and severe clinical presentation. However, this case suggests that it can also manifest with chronic, protracted changes. The possibility of \u003cem\u003eL.longbeachae\u003c/em\u003e infection should be considered even in immunocompetent individuals with CAP. mNGS may be the most effective tool for diagnosing \u003cem\u003eL.longbeachae\u003c/em\u003e infection.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCAP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ecommunity-acquired pneumonia\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cem\u003eL.longbeachae\u003c/em\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eLegionella longbeachae\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWBC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ewhite blood cell\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCRP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eC-reactive protein\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLDH\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003elactate dehydrogenase\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eposteroanterior radiograph\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBNP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ebrain natriuretic peptide\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePaCO₂\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epartial pressure of carbon dioxide\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePaO₂\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epartial pressure of oxygen\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eRBC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ered blood cell\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePLT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eplatelet\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCEA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ecarcinoembryonic antigen\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAFP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ealpha-fetoprotein\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBAL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ebronchoalveolar lavage\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003emNGS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003emetagenomic next-generation sequencing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHHV-1\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eHuman herpesvirus 1\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCK\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ecreatine kinase\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCK-MB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ecreatine kinase-MB isoenzyme\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCTPA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCT pulmonary angiography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEBUS-TBNA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eendobronchial ultrasound-guided transbronchial needle aspiration\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eUAT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eurinary antigen testing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePCR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epolymerase chain reaction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research has complied with the Declaration of Helsinki and has been approved by\u0026nbsp;Ethics Committee in Clinical Research\u0026nbsp;of The First Hosptial of Jiaxing, China. Informed consent to participate was obtained from all the participants.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from the patient for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data and images presented in this article are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY.X. and L.C.: collected data, wrote the main manuscript text. X.M.: critically reviewed and approved the final version of manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe are appreciative of patient and her representative for agreement to this publication.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eCunha BA, Burillo A, Bouza E. Legionnaires\u0026apos; disease. Lancet (London, England). 2016;387(10016):376-85.\u003c/li\u003e\n \u003cli\u003eChahin A, Opal SM. Severe Pneumonia Caused by Legionella pneumophila: Differential Diagnosis and Therapeutic Considerations. Infectious disease clinics of North America. 2017;31(1):111-21.\u003c/li\u003e\n \u003cli\u003eRello J, Allam C, Ruiz-Spinelli A, Jarraud S. Severe Legionnaires\u0026apos; disease. Annals of intensive care. 2024;14(1):51.\u003c/li\u003e\n \u003cli\u003eMondino S, Schmidt S, Rolando M, Escoll P, Gomez-Valero L, Buchrieser C. 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Predictors of intensive care unit admission in patients with Legionella pneumonia: role of the time to appropriate antibiotic therapy. Infection. 2021;49(2):321-5.\u003c/li\u003e\n \u003cli\u003eRuiz-Spinelli A, Rello J. Legionella pneumonia in hospitalized adults with respiratory failure: Quinolones or macrolides? European journal of internal medicine. 2024;120:62-8.\u003c/li\u003e\n \u003cli\u003eDagan A, Epstein D, Mahagneh A, Nashashibi J, Geffen Y, Neuberger A, et al. Community-acquired versus nosocomial Legionella pneumonia: factors associated with Legionella-related mortality. European journal of clinical microbiology \u0026amp; infectious diseases : official publication of the European Society of Clinical Microbiology. 2021;40(7):1419-26.\u003c/li\u003e\n \u003cli\u003eCunha CB, Cunha BA. Antimicrobial Therapy for Legionnaire\u0026apos;s Disease: Antibiotic Stewardship Implications. Infectious disease clinics of North America. 2017;31(1):179-91.\u003c/li\u003e\n \u003cli\u003eZhu A, Ma Q, Liu Z. Omadacycline for the treatment of patients with Legionella pneumophila pneumonia after experiencing liver dysfunction: case series. Frontiers in microbiology. 2024;15:1408443.\u003c/li\u003e\n \u003cli\u003eLi B, Liu L, Li F, He C, Chen Y, Tian X, et al. Omadacycline successfully treated severe Legionella pneumonia after moxifloxacin treatment failure: Case series. Frontiers in pharmacology. 2025;16:1559857.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Medicine](https://link.springer.com/journal/44337)","snPcode":"44337","submissionUrl":"https://submission.springernature.com/new-submission/44337/3","title":"Discover Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Legionella longbeachae, cavity-type pneumonia","lastPublishedDoi":"10.21203/rs.3.rs-9115058/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9115058/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLegionella is a common causative pathogen of community-acquired pneumonia, but it encompasses multiple subtypes, with Legionella longbeachae \u003cem\u003e(\u003c/em\u003eL. longbeachae\u003cem\u003e)\u003c/em\u003e not being the most frequently encountered. Cavitary pneumonia is exceedingly rare in immunocompetent individuals, and cavitary pneumonia caused specifically by L. longbeachae in such patients is even more uncommon.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase presentation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe describe a case of a 77-year-old female patient whose primary clinical manifestations were cough and myalgia. As the disease progressed, the patient gradually developed multiple cavities in the lower lobe of the right lung, exhibiting a chronic, protracted course. Metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid on two separate occasions indicated the presence of L. longbeachae. During hospitalization, she received sequential anti-infective therapy with levofloxacin, nemonoxacin, and omadacycline, ultimately improving and being discharged.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis represents the first definitively diagnosed case of cavitary pneumonia caused by L. longbeachae in a completely immunocompetent patient in the Chinese region. This case highlights the importance of maintaining clinical suspicion and confirms the value of applying mNGS in clinical infectious disease scenarios. The judicious use of quinolones or novel tetracycline derivatives demonstrates good efficacy against L. longbeachae.\u003c/p\u003e","manuscriptTitle":"A case report of cavitary pneumonia caused by Legionella longbeachae in an immunocompetent patient","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-08 16:17:46","doi":"10.21203/rs.3.rs-9115058/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-17T13:41:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"288870192361304072979339653428426077319","date":"2026-05-09T10:59:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"67138871026907669578810378263137385692","date":"2026-04-26T16:02:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-23T17:28:17+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-01T13:18:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-25T16:56:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-25T13:53:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Medicine","date":"2026-03-25T13:47:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Medicine](https://link.springer.com/journal/44337)","snPcode":"44337","submissionUrl":"https://submission.springernature.com/new-submission/44337/3","title":"Discover Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1d1b98f5-1fff-4989-aa75-0be4fecad5b1","owner":[],"postedDate":"May 8th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-17T13:41:54+00:00","index":62,"fulltext":""},{"type":"reviewerAgreed","content":"288870192361304072979339653428426077319","date":"2026-05-09T10:59:12+00:00","index":59,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T16:17:47+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-08 16:17:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9115058","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9115058","identity":"rs-9115058","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}