Risk factors for surgical site infections following microwave ablation of the uterus: a retrospective cohort study

Table 1 Variables used in the analysis Variables Categories Specific Variables Patient demographics Age, BMI, Parity, Previous surgery, Preoperative GnRHa, ASA grade. Comorbidities Preoperative anemia, diabetes, hypertension, comorbidities without medical treatment. Operative and disease information Surgical duration, adhesion or not, type of disease, tumor size, tumor number, prophylactic antibiotics, blood transfusion. Preoperative blood routine index White blood cell count, neutrophil count, hemoglobin count, platelet count. BMI: body mass index; GnRHa: gonadotropin releasing hormone agonist; ASA grade: American Society of Anesthesiologists Classification; Comorbidities without medical treatment: General complications do not require the use of drugs to control; Variables used in the analysis Age, BMI, Parity, Previous surgery, Preoperative GnRHa, ASA grade. BMI: body mass index; GnRHa: gonadotropin releasing hormone agonist; ASA grade: American Society of Anesthesiologists Classification; Comorbidities without medical treatment: General complications do not require the use of drugs to control; 214 patients underwent microwave ablation (MWA) at The First Affiliated Hospital of the University of Science and Technology of China between December 2020 and November 2023. Three patients were excluded due to incomplete data, resulting in a final sample of 211 patients. Among these, 16 patients developed surgical site infections (SSIs), representing an overall infection rate of 7.58% (see Table  2 ). Table 2 Baseline characteristics of the study population (2020.12-2023.11) Characteristics Infection No Infection P Total ( n  = count) 16 195 Total incidence (%) 7.58 Age (median, IQR, years) 42.5 (38-45.75) 40 (35–44) 0.168 Surgical duration (median, IQR, minutes) 160 (121.25–201) 90 (74–112) < 0.001 White blood cell count (median, IQR, ×10 9 /liter) 5.63(4.48–7.08) 5.54(4.59–6.68) 0.958 Neutrophil count (median, IQR, ×10 9 /liter) 3.20(2.71–4.11) 3.26(2.48–4.20) 0.816 Hemoglobin count (median, IQR, gram/liter) 119(105-126.5) 122(106–131) 0.439 Platelet count (mean, IQR, ×10 9 /liter) 249.75 ± 79.43 263.97 ± 73.38 0.460 BMI ≤ 23 kg/m 2 95(48.7%) 100(51.3%) 0.562 > 23 kg/m 2 9(56.3%) 7(48.3%) Parity Nulliparous women 4(25%) 45(23.1%) 0.861 Parous women 12(75%) 150(76.9%) Previous surgery No 8(50%) 96(49.2%) 0.953 Yes 8(50%) 99(50.8%) Preoperative GnRH Agonist No 15(93.8%) 164(84.1%) 0.502 Yes 1(6.3%) 31(15.9%) ASA grade 1 2(8.3%) 14(7.5%) 0.883 2 22(91.7%) 173(92.5%) BMI: Body Mass Index; GnRH: gonadotropin-releasing hormone; ASA grade: American Society of Anesthesiologists Classification Baseline characteristics of the study population (2020.12-2023.11) White blood cell count (median, IQR, ×10 9 /liter) Neutrophil count (median, IQR, ×10 9 /liter) Hemoglobin count (median, IQR, gram/liter) Platelet count (mean, IQR, ×10 9 /liter) BMI: Body Mass Index; GnRH: gonadotropin-releasing hormone; ASA grade: American Society of Anesthesiologists Classification The comparison of baseline characteristics between the infection and non-infection groups showed no significant differences in age (42.5 vs. 40 years, P  = 0.168), body mass index (BMI) ( P  = 0.562), or parity ( P  = 0.861). Additionally, prior surgery ( P  = 0.953) and preoperative GnRHa treatment ( P  = 0.502) were similar across groups, as were blood routine tests, including white blood cell count ( P  = 0.958), neutrophil count ( P  = 0.816), hemoglobin count ( P  = 0.439), and platelet count ( P  = 0.460). These results indicate that baseline characteristics were comparable between the two groups (Table  2 ). A significant difference was observed in surgical duration between groups, with median times of 160 min (121.25–201, IQR) in the infection group versus 90 min (74–112, IQR) in the non-infection group ( P  < 0.001) and the 180-minute operative time cut-off was used as a threshold based on its high association with infection risk, with patients experiencing operative times over 180 min having 14.39 times increased risk of SSI (OR 14.39, 95% CI: 4.44–46.59, P  < 0.001). Prolonged operative times in MWA can increase exposure to environmental contaminants and lead to tissue dryness, elevating infection risk. Minimizing surgical time may be achieved by optimizing preoperative preparation and intraoperative efficiency. Abdominal adhesions also emerged as a significant independent risk factor for SSIs (OR 4.58, 95% CI: 1.18–17.86, P  = 0.028) (Tables  3 and 4 ). Table 3 Information of the perioperative situation (2020.12-2023.11) Characteristics Infection No Infection P Surgical duration < 180 min 9(56.3%) 185(94.9%) < 0.001 ≥ 180 min 7(43.8%) 10(5.1%) Type of Disease Uterine myomas 82(42.1%) 4(25%) 0.387 Adenomyosis 83(42.6%) 9(56.3%) Both uterine myomas and adenomyosis 30(15.4%) 3(18.8%) Multiple uterine fibroids Single 1(25%) 28(34.1%) 0.699 Multiple 3(75%) 54(65.9) Adhesion No 4(25%) 114(59.1%) 0.008 Yes 12(75%) 79(40.9%) Prophylactic antibiotics Cefoxitin 162(83.1%) 16(100%) 0.091 Cefuroxime 28(14.4%) 0(0%) Clindamycin 5(2.6%) 0(0%) Blood transfusion No 16(100%) 194(99.5%) 0.691 Yes 0(0%) 1(0.5%) Tumor size (median, IQR, centimeters) 6(5-9.25) 6(5–7) 0.449 Information of the perioperative situation (2020.12-2023.11) Tumor size (median, IQR, centimeters) Table 4 Risk factors associated with surgical site infection Variable Multivariate Logistic Regression OR 95% CI P Surgical duration < 180 min Ref —— —— ≥ 180 min 14.39 4.44–46.59 <0.001 Surgical indication Uterine myomas Ref —— —— Adenomyosis 0.88 0.16–5.03 0.888 Both of uterine fibroid and adenomyosis 1.38 0.30–6.41 0.682 Multiple uterine myomas Single Ref —— —— Multiple 1.56 0.16–15.65 0.708 Adhesion No Ref —— —— Yes 4.58 1.18–17.86 0.028 OR: Odds ratio, CI: Confidence interval Risk factors associated with surgical site infection OR: Odds ratio, CI: Confidence interval The risk of SSIs did not vary significantly with different surgical indications (uterine myomas, adenomyosis, or both), with a P -value of 0.387 (see Table  3 ). Similarly, the type of prophylactic antibiotics used, whether cefoxitin, cefuroxime, or clindamycin, did not significantly impact SSI risk ( P  = 0.091). Myomas’ number ( P  = 0.699) and size ( P  = 0.449) were not associated with increased SSI risk. Due to the small sample size of patients receiving blood transfusions, no significant relationship was observed between transfusion and SSI occurrence ( P  = 0.691). Detailed results are presented in Tables  3 and 4 , and Fig.  1 . An assessment of preoperative comorbidities showed no significant association with SSI risk, including anemia ( P  = 0.917), diabetes ( P  = 0.194), hypertension ( P  = 0.257), and other comorbidities that did not require medical treatment, such as a history of syphilis, hepatitis B infection, and arrhythmia ( P  = 0.963). These data are summarized in Table  5 . Table 5 Relationship between infection and preoperative comorbidities Comorbidities Univariate Analysis Multivariate Logistic Regression No infection Infection P OR 95% CI P Preoperative anemia 52 (26.7%) 5 (31.3%) 0.917 1.25 0.42–3.77 0.692 Diabetes 2 (1.0%) 1 (6.3%) 0.194 - - - Hypertension 8 (4.1%) 0 (0%) 0.257 - - - Other comorbidities without medical treatment 72(36.9%) 6(37.5%) 0.963 1.20 0.37–3.86 0.760 OR: Odds ratio, CI: Confidence interval Relationship between infection and preoperative comorbidities OR: Odds ratio, CI: Confidence interval Figure 1 illustrates the distribution of disease types (fibroids, adenomyosis, or both) and the types of antibiotics administered as prophylaxis to prevent SSIs among patients undergoing MWA. Antibiotic data were collected from patient medical records, documenting the prophylactic use of cefoxitin, cefuroxime, and clindamycin, based on patient allergy history. These antibiotics were administered 30 min before surgery, with an additional dose provided if the operation exceeded three hours. Fig. 1 Distribution of disease types and antibiotic prophylaxis in patients undergoing microwave ablation (MWA) Results– Type of Disease and Antibiotic Prophylaxis. Panel A : Distribution of disease types among patients with SSIs. Panel B : Disease types among patients without SSIs. Panel C : Antibiotic use in SSI group. Panel D : Antibiotic use in non-SSI group Distribution of disease types and antibiotic prophylaxis in patients undergoing microwave ablation (MWA) Results– Type of Disease and Antibiotic Prophylaxis. Panel A : Distribution of disease types among patients with SSIs. Panel B : Disease types among patients without SSIs. Panel C : Antibiotic use in SSI group. Panel D : Antibiotic use in non-SSI group

A retrospective analysis was conducted at The First Affiliated Hospital of the University of Science and Technology of China in Hefei, Anhui Province. The study included patients who underwent MWA between December 2020 and November 2023. This study received ethical approval from the Institutional Review Board, with Ethics Approval Number 2024-RE-219. The information on women who underwent MWA during the study period was obtained from hospital inpatient records. Data collected included demographic information such as body mass index (BMI), parity, and age. Clinical data encompassed the type of disease, largest dimension of tumors, number of myomas, previous surgeries, smoking status, use of preoperative gonadotropin-releasing hormone agonist (GnRHa), preoperative comorbidities, prophylactic antibiotic use, and blood examination results. Operative data included blood transfusions, operative time, intraoperative blood loss, and the American Society of Anesthesiologists (ASA) Classification. Patients with ASA classification III or higher were excluded during preoperative assessment due to higher operative risk and institutional surgical policy regarding elective MWA procedures. Postoperative data included any febrile morbidity observed after the procedure. Antibiotic data were collected from patient medical records, capturing the type and timing of antibiotic administration for prophylaxis. These antibiotics, chosen based on patient allergy history, were administered 30 min before surgery to prevent SSIs, with an additional dose given if the operation exceeded three hours (Table 1 ). Inclusion criteria included: (1) age 18–55 years; (2) undergoing laparoscopic MWA performed by our team; (3) diagnosis of myoma or adenomyosis; and (4) providing written informed consent for the operation; (5) the absence of any active systemic infection at the time of surgery. Exclusion criteria were incomplete data or failure to meet the above selection criteria. Surgical site infections (SSIs) were diagnosed based on CDC criteria, including clinical signs of infection (erythema, warmth, tenderness, or purulent drainage), elevated inflammatory markers, and confirmation via imaging or microbiological evidence where applicable [ 11 ]. To further explore potential associations, patients were categorized into SSI-present (Groups A and C) and SSI-absent (Groups B and D) groups for subgroup analysis based on disease type and antibiotic prophylaxis. This homogeneous grouping ensured comparability between cases and controls, addressing concerns about population differences. In this study, MWA was performed laparoscopically by the gynecology department at The First Affiliated Hospital of the University of Science and Technology of China. The procedure utilized the ECO-100 A system (Nanjing ECO Microwave System Co. LTD, China) with power settings ranging from 0 to 150 W (typically 55 W), adjusted according to tumor size. A Foley catheter was inserted before the operation and removed within 24 h post-operation. Prophylactic antibiotics, selected based on the patient’s allergy history, were administered intravenously 30 min before the surgery and continued for one day as per drug instructions. An additional dose was given if the operation exceeded 3 h. For patients with heavy menstruation requiring anemia treatment, a GnRH agonist was administered before surgery. This retrospective study assessed the risk factors associated with SSIs following MWA procedures. The study adhered to STROCSS 2024 guidelines, ensuring clarity and reproducibility, and included a comprehensive evaluation of variables, chosen based on established risk factors for SSIs in surgical procedures [ 15 ]. The Kolmogorov-Smirnov test was used to assess the normality of continuous variables, with results confirming the distribution type for each variable. The Student’s t-test was used for normally distributed continuous variables, while non-normally distributed variables were analyzed using the Wilcoxon and Mann-Whitney tests. Categorical variables were examined using the chi-square test. Multivariate logistic regression analysis was conducted, including surgical duration, abdominal adhesion, smoking status, and ASA classification as factors, with post-estimation goodness-of-fit tests applied to assess model validity. Sample size calculations indicated that a minimum of 200 patients was required to achieve sufficient power to detect differences in SSI incidence. Statistical analysis was performed using IBM SPSS 26.0, with significance defined as P  < 0.05. The variables included in multivariate logistic regression were selected based on clinical relevance and previously established risk factors for surgical site infection in gynecologic and abdominal surgeries [ 16 – 18 ]. Sample size calculations were based on an assumed SSI incidence difference of 10% between groups, a power of 80%, and a significance level of 0.05. A minimum of 200 patients was required to detect this difference using a two-tailed test.

SSIs occurred in 7.58% of patients following MWA. Surgical duration and abdominal adhesions were significantly associated with increased SSI risk. At the same time, age, BMI, parity, blood routine tests, previous surgeries, and preoperative GnRHa treatment did not demonstrate any significant impact. Additionally, myoma volume and size were not associated with SSI development. In the context of prescriptive prophylactic antibiotic use, abdominal adhesions and extended operative times remain key risk factors for postoperative SSIs. Surgeons need to minimize postoperative abdominal adhesions and actively pursue strategies to reduce operative time, helping mitigate the risk of surgical complications and improve patient outcomes. This is one of the first studies to specifically look at what increases the risk of surgical site infections (SSIs) after microwave ablation (MWA) of the uterus in a Chinese population. Since MWA is becoming more common, understanding these risks is very important for patient safety.

Adenomyosis and myoma are common conditions affecting women of childbearing age, with treatment options ranging from procedural to medical approaches, depending on factors such as symptoms, tumor size, and position, as well as patient and physician awareness of alternative therapies [ 3 – 6 ]. In recent years, interest has grown in uterine-preserving, minimally invasive procedures, including high-intensity focused ultrasound (HIFU), uterine artery embolization (UAE), radiofrequency ablation, and microwave ablation (MWA) [ 19 – 22 ]. Among these, MWA offers the advantages of minimal invasiveness, reduced trauma, and faster recovery, with the added benefit of potentially preserving ovarian reserve better than UAE, making it a favorable treatment option, particularly in Asia [ 9 ]. MWA uses electromagnetic microwaves to induce heat and coagulation necrosis, effectively shrinking fibroids and alleviating symptoms, with the highest utilization rates in China and Japan [ 19 , 23 , 24 ]. However, surgical site infections (SSIs) remain a concern following MWA, as these infections can negatively impact patient outcomes and increase healthcare costs. Hospitals have implemented comprehensive measures to prevent SSIs, including the selection and timing of preoperative antibiotics [ 25 ]. Despite these efforts, achieving consistent control over SSIs remains challenging. Our study revealed that 7.58% of patients developed SSIs following MWA. We identified prolonged surgical duration and abdominal adhesions as independent SSI risk factors. This aligns with findings in previous studies that prolonged surgical duration is associated with increased SSI risk [ 16 ]. For example, a multicenter retrospective study found a direct association between hysterectomy duration and postoperative infection, with prolonged surgical duration identified as the only independent risk factor for post-surgery SSIs [ 17 ]. Prolonged exposure to the operating room environment may increase the risk of bacterial contamination, and tissue dryness due to extended exposure may further elevate infection risk [ 18 , 26 ]. These findings emphasize the need for surgical teams to implement strategies that minimize operative time, such as streamlining preoperative preparation and enhancing intraoperative efficiency, which may reduce the risk of SSIs. Abdominal adhesions, often a factor in extended surgical durations, also increase the risk of SSIs. Larger separations in adhesive wounds can lead to more inflammatory exudation and bleeding, increasing infection susceptibility. Preventative measures to reduce postoperative adhesion formation should be considered to enhance surgical safety. Our study found no significant correlation between the choice of prophylactic antibiotics and the incidence of SSIs. This could be due to the limited sample size, which may have reduced the statistical power needed to detect significant differences. Consistent with earlier studies that failed to identify a superior antibiotic choice, most guidelines recommend a combination of antibiotics during hysterectomy procedures to optimize SSI prevention [ 27 , 28 ]. Additionally, neither myomas’ number nor size significantly impacted SSI occurrence, which aligns with previous research findings [ 29 ]. Recent evidence has also highlighted the potential risks of surgical smoke, including the possibility of infection, tumor cell spread, and metastasis [ 30 ]. The longer the operation time is, the more severe the intraoperative adhesion will be, which means more surgical operations and also more surgical smoke. This may be one of the reasons for the occurrence of SSI. While our study did not directly assess the role of surgical smoke, this remains an important area for further investigation, particularly in minimally invasive procedures such as microwave ablation. This research mainly has the following advantages: Strong Research Design: We used a detailed and structured retrospective study, collecting a wide range of data—from patient background to lab tests—to carefully analyze potential risk factors. Well-Defined Patient Group: All patients were treated at the same high-volume hospital, which helped reduce differences in surgical technique or environment and made the findings more reliable. Clear Risk Factors Identified: We found that longer surgeries and the presence of abdominal adhesions are key risk factors for infection. Since these factors can be addressed or managed, our findings can help guide better surgical planning and care. New Contribution: There is very little published research on SSIs after MWA. Our study helps fill this gap, especially for patients with uterine fibroids or adenomyosis. The study showed no statistically significant association between various preoperative comorbidities (e.g., anemia, diabetes, hypertension) and the risk of SSIs. This lack of association may be partly due to our clinical practice of managing and stabilizing uncontrolled comorbidities before surgery, reducing their potential impact on postoperative complications. This study has several limitations: (1) Being a retrospective study, it may include inherent biases typical of this design, such as selection bias. (2) The sample size, while notable, may limit the generalizability of certain findings, especially in subgroup analyses. (3) The study was conducted at a single medical center, which may restrict the generalizability of the results to other institutions. Future multicenter, prospective studies with larger patient populations are needed to validate these findings and potentially refine risk factors for SSIs following MWA.

Uterine myoma and adenomyosis are the most common benign uterine conditions in women of reproductive age and often coexist. Myomas occur in about 25% of cases, while the clinical prevalence of adenomyosis averages between 20% and 30% [ 1 , 2 ]. These conditions can lead to abnormal uterine bleeding, dysmenorrhea, dyspareunia, and infertility, significantly impacting women’s health [ 3 ]. Adenomyosis and myoma can be treated using medical or procedural methods, including minimally invasive therapies and surgery [ 4 – 6 ]. Recently, microwave ablation (MWA) has become a crucial treatment option for both conditions [ 7 – 9 ]. MWA is widely used to treat uterine myoma and adenomyosis; however, it also carries a risk of surgical complications [ 9 , 10 ]. Surgical site infections (SSIs) are among the most common complications of MWA. SSIs encompass pelvic abscess formation, deep incisional abscesses, superficial incisional cellulitis, and pyometra [ 11 ]. The incidence of SSIs ranges from about 3–20% [ 12 ]. These infections are linked to higher mortality, increased healthcare costs, and extended hospital stays. Thus, early identification of risk factors is clinically crucial [ 12 – 14 ]. However, no studies have examined the risk factors for SSIs following uterine MWA. To address this, we conducted a retrospective review of women who underwent MWA at a university-affiliated tertiary medical center, aiming to identify potential SSI risk factors. This retrospective cohort study has been reported in line with the STROCSS 2024 guidelines [ 15 ].