Phases of Leptospirosis
Leptospirosis presents as a biphasic illness with an initial septicemic phase lasting 4-7 days, followed by an immune-mediated phase where antibodies cause secondary manifestations. 1, 2
Septicemic (Bacteremic) Phase
This first phase lasts 4-7 days and represents the period of active bacterial dissemination through the bloodstream. 1, 2
Clinical features include:
- High fever, typically 39°C or higher 1
- Diffuse myalgias, particularly severe in the calf muscles 1
- Severe headache 1
- Conjunctival suffusion (a highly suggestive finding—redness of the conjunctiva without discharge) 1
- Chills and malaise 3, 2
During this phase, leptospires are present in blood and cerebrospinal fluid and can be isolated through culture (ideally within the first 5 days before antibiotics). 1 The presentation often mimics influenza or dengue fever, making early diagnosis challenging. 4
Immune (Leptospiruric) Phase
The second phase begins as leptospires disappear from blood and cerebrospinal fluid, replaced by circulating antibodies that trigger immune-mediated complications. 2, 5
Clinical manifestations include:
- Aseptic meningitis (most common immune manifestation) 2, 6
- Uveitis 2
- Rash 2
- In severe cases (Weil's disease, occurring in 5-10% of infections): jaundice, hemorrhage, and hepato-renal failure 1, 2
Important Clinical Considerations
The biphasic pattern is not always distinct. Many patients in endemic areas experience mild or asymptomatic infections without clear phase separation. 4 In severe leptospirosis, symptoms may progress continuously without an obvious immune phase demarcation. 4
Timing matters for diagnosis: Blood cultures are most useful during the septicemic phase (first 5 days), while serology becomes positive during the immune phase, with IgM titers >1:320 being suggestive and convalescent serology (>10 days after symptom onset) confirming diagnosis. 1
Treatment should not wait for phase confirmation. Antibiotics (penicillin or doxycycline) should be initiated immediately upon clinical suspicion, as each hour of delay in severe cases increases mortality. 1 Even when started after the septicemic phase, antibiotics remain effective in severe disease. 2
Common pitfall: The symptoms during the initial septicemic phase are nonspecific and easily confused with viral illnesses, leading to delayed diagnosis and treatment beyond the critical 4-day window when antibiotics are most effective. 1, 6