BEYOND EPIDEMIOLOGY: THE IMPORTANCE OF MOLECULAR METHODS IN THE DIAGNOSIS OF ATYPICAL PNEUMONIAS

Accurate initial diagnosis of acute febrile syndromes with multisystem involvement can be challenging. Leptospirosis, caused by Leptospira spp., is often associated with environmental or occupational exposure, whereas Legionnaires’ disease, caused by Legionella pneumophila , is linked to inhalation of contaminated aerosols. Both conditions may present with similar symptoms, making differentiation essential for appropriate treatment. We report a case of fever, renal failure and rhabdomyolysis as manifestations of an underdiagnosed disease. A 61-year-old male, hypertensive and smoker, was brought by a family member to the emergency department of a tertiary private hospital after onset of high fever, vomiting, diarrhea and lower-limb myalgia. He had returned from Colonia del Sacramento (Uruguay) three days earlier. On admission, he was hemodynamically stable but somnolent, with laboratory results showing leukocytes 17,800/µL (8% bands), creatinine 4.1 mg/dL, urea 88 mg/dL, C-reactive protein 436.9 mg/L and creatine kinase 9,906 U/L. Serology and PCR (reverse transcription polymerase chain reaction) for Leptospira spp. were requested, and ceftriaxone 2g/day IV was started. On the third hospital day, the patient developed hypoxia; chest CT revealed extensive consolidation in the right upper lobe and scattered ground-glass opacities in the right lung, suggestive of alveolar hemorrhage. The patient was intubated due to respiratory failure and underwent bronchoalveolar lavage. The sample was tested with the FilmArray® pneumonia molecular panel, which detected Legionella pneumophila . Antibiotic therapy was switched to azithromycin 500 mg IV, and moxifloxacin 400 mg/day IV was added 48 hours later due to disease severity. During hospitalization, he required hemodialysis to recover renal function and remained intubated for eleven days. PCR for leptospirosis was negative. The patient was discharged 27 days after admission with full recovery. This case reinforces the importance of rapid molecular methods for the diagnosis of severe atypical pneumonias, even when the epidemiologic history initially suggests leptospirosis, enabling targeted therapy and better outcomes.