Differential Diagnosis

The patient's presentation is complex, with multiple symptoms and laboratory findings that could suggest several diagnoses. Here's a categorized differential diagnosis based on the provided information:

• Single most likely diagnosis
  • Severe Leptospirosis with Multi-Organ Dysfunction Syndrome (MODS): Despite the negative Lepto PCR, the clinical presentation (exposure to rainwater, fever, jaundice, renal impairment, and thrombocytopenia) and the initial response to treatment suggest leptospirosis. Leptospirosis can present with a wide range of symptoms, and PCR may be negative early in the disease or due to prior antibiotic use.
• Other Likely diagnoses
  • Sepsis (cellulitis-induced) with MODS: The patient has cellulitis, which could be the source of sepsis, especially with the progression of ankle swelling and the presence of fever, tachycardia, and elevated procalcitonin levels.
  • Viral Hepatitis: Although serology for common viral hepatitis (HAV, HEV) is negative, other forms of viral hepatitis or a non-viral cause of hepatitis could be considered, given the patient's jaundice and abnormal liver function tests.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Meningococcemia: Although the patient does not have a typical rash, meningococcemia can present with fever, shock, and multi-organ failure. It's crucial to consider this diagnosis due to its high mortality rate if not promptly treated.
  • Rickettsial Diseases: Given the fever, exposure to potential vectors (through rainwater), and the presence of thrombocytopenia, rickettsial diseases like scrub typhus or spotted fever could be considered, especially if the patient has been in an endemic area.
• Rare diagnoses
  • Hantavirus Syndrome: This viral infection can cause fever, renal failure, and thrombocytopenia, although it is less common and typically associated with specific geographic locations and exposure to rodents.
  • Relapsing Fever (Borrelia): Characterized by recurring episodes of fever, this diagnosis might be considered if the patient's symptoms recur after initial improvement, although it's less likely given the current presentation.

Each of these diagnoses should be considered in the context of the patient's clinical presentation, epidemiological history, and laboratory findings. The treatment should be tailored based on the most likely diagnosis and adjusted as necessary based on the patient's response and additional diagnostic information.