A 28-year-old male farmer from rural Maharashtra presents with a 5-day history of high fever (40°C), severe headache, myalgia, and conjunctival suffusion without exudate. On day 6, he develops jaundice, oliguria, and acute kidney injury (creatinine 3.2 mg/dL). Blood culture is negative. Urine microscopy shows muddy brown casts. What is the most likely diagnosis?

## Clinical Diagnosis: Leptospirosis (Weil's Disease) ### Key Clinical Features **Key Point:** Leptospirosis presents in two phases — the leptospiremic (septicemic) phase lasting 3–7 days, followed by the immune phase with potential organ involvement. This patient exhibits the classic biphasic presentation: - **Leptospiremic phase (days 1–5):** High fever, severe headache, myalgia, conjunctival suffusion (pathognomonic redness without exudate) - **Immune phase (day 6 onwards):** Jaundice, oliguria, acute kidney injury (Weil's disease) ### Why This Is Weil's Disease **High-Yield:** Conjunctival suffusion WITHOUT exudate is a hallmark sign of leptospirosis and distinguishes it from other febrile illnesses. The combination of: 1. Occupational exposure (farmer — water contact) 2. Biphasic fever pattern 3. Conjunctival suffusion 4. Acute kidney injury with muddy brown casts (acute tubular necrosis) 5. Jaundice (hepatic involvement) ...defines Weil's disease, the severe form of leptospirosis. ### Pathophysiology **Clinical Pearl:** Leptospira interrogans serovars (especially Icterohaemorrhagiae and Copacabana) cause direct tissue invasion during the immune phase, leading to vasculitis, capillary leak, and multi-organ failure. The muddy brown casts indicate myoglobinuria and hemoglobinuria from hemolysis and rhabdomyolysis, compounding renal injury. ### Diagnostic Confirmation | Phase | Day | Diagnostic Method | Specimen | |-------|-----|-------------------|----------| | Leptospiremic | 1–7 | Blood culture, PCR | Blood | | Immune | 7–30 | MAT (gold standard), IgM ELISA | Serum, CSF | | Late | >30 | Urine culture | Urine | **Tip:** Blood culture is often negative by day 6 (immune phase has begun), so negative blood culture does not exclude leptospirosis. ### Management **Key Point:** Early antibiotic therapy (doxycycline or penicillin) in the leptospiremic phase reduces severity; supportive care and dialysis are critical in Weil's disease. [cite:Park 26e Ch 6]