Leptospirosis-induced diffuse alveolar hemorrhage: A rare case report from a non-epidemic area and literature review.

RATIONALE: Leptospirosis is an uncommon cause of severe pneumonia and diffuse alveolar hemorrhage (DAH), particularly in non-endemic areas, posing a significant diagnostic challenge. This case highlights the critical role of advanced molecular diagnostics in identifying this rare and life-threatening presentation.

PATIENT CONCERNS: A 65-year-old woman presented with an acute onset of high fever, chest tightness, and rapidly progressive shortness of breath.

DIAGNOSES: The patient was initially misdiagnosed with severe community-acquired pneumonia. She subsequently developed septic shock and multiple organ dysfunction syndrome. A definitive diagnosis of leptospirosis-induced DAH was confirmed through metagenomic next-generation sequencing, reverse transcription quantitative PCR, and subsequent seroconversion shown by immunoglobulin M enzyme-linked immunosorbent assay.

INTERVENTIONS: Upon diagnosis, targeted antimicrobial therapy with intravenous penicillin was initiated. Supportive care included management of septic shock and lung-protective ventilation for concomitant acute respiratory distress syndrome.

OUTCOMES: Following the confirmation of leptospirosis and initiation of targeted treatment, the patient's condition gradually stabilized. After a course of intensive care, she made a full recovery and was successfully discharged.

LESSONS: This case underscores that leptospirosis can present as fulminant DAH even in non-endemic regions. A high index of suspicion, aided by epidemiological clues and the rapid application of metagenomic next-generation sequencing/reverse transcription quantitative PCR, is crucial for timely diagnosis. Prompt targeted antimicrobial therapy combined with intensive organ support is essential for a favorable outcome in severe cases.