Clinical Course of Leptospirosis
Leptospirosis classically follows a biphasic course with an incubation period of 7-12 days (range 2-30 days), followed by an initial bacteremic phase lasting 4-7 days with flu-like symptoms, then 1-3 days later an immune phase characterized by fever, severe calf myalgia, hepatorenal syndrome, and hemorrhage 1.
Incubation Period
The incubation period ranges from 7 to 12 days, though it can extend from 2 to 30 days after exposure to contaminated water or animal urine 1. During this time, leptospires penetrate mucous membranes or skin breaks and disseminate throughout the body 2.
Phase 1: Septicemic/Bacteremic Phase (Days 1-7)
This initial phase lasts 4-7 days and presents with non-specific flu-like symptoms 1:
- Fever
- Myalgia (muscle pain, particularly in the calves)
- Headache
- Conjunctival suffusion (a suggestive finding)
- Mild disease is generally self-limiting
During this phase, leptospires are present in blood and CSF, making blood cultures positive if taken within the first 5 days before antibiotics 1. The clinical presentation varies from mild flu-like symptoms to severe illness 1.
Interphase (Days 1-3)
Following the septicemic phase, there is a 1-3 day interval where symptoms may temporarily resolve before the immune phase begins 1, 3.
Phase 2: Immune Phase (Days 10-30)
During this second phase, leptospires disappear from blood and CSF, but circulating antibodies trigger immune-mediated complications 2:
- Fever recurrence
- Severe myalgia (especially calves)
- Hepatorenal syndrome
- Hemorrhagic manifestations (due to capillary fragility, not clotting abnormalities)
- Aseptic meningitis
- Uveitis
- Rash
Serological tests become positive 6-10 days after symptom onset, with IgM titers >1:320 considered suggestive of leptospirosis 1.
Severe Disease: Weil's Disease
Approximately 5-10% of infected patients develop severe leptospirosis (Weil's disease) characterized by 2, 4:
- Jaundice (high bilirubin with mild transaminase elevation)
- Acute kidney injury (may require hemodialysis)
- Hemorrhagic complications (pulmonary hemorrhage, hemoptysis)
- Hepatorenal failure
- Rhabdomyolysis
- Cardiac complications (myocarditis, arrhythmias, rarely cardiac tamponade)
Pulmonary involvement occurs in 20-70% of patients, with severe pulmonary hemorrhagic syndrome carrying approximately 50% mortality, with death typically occurring within 72 hours of symptom onset 5.
Critical Clinical Pitfalls
Conjunctival suffusion is a highly suggestive clinical finding that should prompt immediate consideration of leptospirosis 1. The combination of calf myalgia, conjunctival suffusion, and exposure history (recreational water sports, flooding, occupational animal contact) should trigger empiric treatment.
Severe disease is probably immunologically mediated, explaining why patients with Weil's disease can deteriorate despite antibiotic therapy and may require intensive organ support (renal replacement, mechanical ventilation) 1. While systematic reviews show limited benefit of antibiotics in established severe disease, most infectious disease specialists continue recommending them, particularly penicillin or tetracycline antibiotics during the bacteremic phase 1.
Treatment should begin upon clinical suspicion given the non-specific nature of initial investigations and the potential for rapid deterioration 1. Waiting for serological confirmation (which takes 6-10 days) can result in progression to severe disease with significantly worse outcomes.