Beyond Antibiotic Failure: A Case of Strongyloides and Coccidioidomycosis Coinfection Presenting with Pulmonary Eosinophilia

Background: Overlapping endemic infections often present with non-specific systemic features, which could initially lead to delayed recognition and inappropriate treatment. Strongyloides stercoralis and Coccidioides spp. are rarely encountered together, yet both may cause pulmonary disease, constitutional symptoms, and eosinophilia, complicating diagnosis. Corticosteroid exposure in particular can unmask severe strongyloidiasis, highlighting the importance of early detection. Case Presentation: We present the case of a 30-year-old man from the Dominican Republic with recent travel to Brazil and Mexico, who presented with a 3-week history of fever, cough, myalgias, rash, and 13-pound weight loss. Initial treatment for presumed asthma exacerbation and bacterial pneumonia with corticosteroids and multiple antibiotics failed to relieve symptoms. Laboratory evaluation revealed marked eosinophilia (absolute eosinophil count 3,400/µL) and elevated inflammatory markers. Chest CT demonstrated diffuse bilateral tree-in-bud and micronodular opacities. Bronchoalveolar lavage contained 44% eosinophils. Serologic testing was positive for Strongyloides IgG, Coccidioides IgM/IgG, and β-D-glucan. The patient improved with ivermectin and fluconazole but experienced a relapse of coccidioidomycosis after antifungal discontinuation, requiring reinitiation of long-term azole therapy. Discussion: Coinfection with Strongyloides stercoralis and Coccidioides spp. poses a difficult diagnosis due to overlapping respiratory and systemic manifestations that could mimic common bacterial, fungal or allergic processes. Corticosteroid exposure can precipitate Strongyloides hyperinfection while promoting fungal proliferation, worsening disease severity. Recognition of eosinophilia in patients with a compatible travel history should prompt evaluation for parasitic and fungal etiologies. This case emphasizes the need for early serologic testing and targeted therapy while providing close follow-up to prevent relapses and complications in overlapping endemic infections. Conclusion: This case shows the difficulty of diagnosing overlapping infections like Strongyloides stercoralis and Coccidioides, which can easily be mistaken for bacterial pneumonia. It highlights the risk of giving corticosteroids before ruling out parasitic diseases and stresses the value of screening those at risk. The patient’s relapse after stopping treatment reflects the chronic nature of coccidioidomycosis and the need for close follow-up. Clinicians should keep an open, exposure-based approach when evaluating unexplained pulmonary symptoms, especially in people from endemic areas. This case underscores the importance of broad differentials, timely diagnosis, and long-term monitoring in patients with complex overlapping infections.