What are the diagnostic steps and treatment options for leptospirosis?

Diagnosis of Leptospirosis

Diagnose leptospirosis clinically based on the characteristic triad of fever with conjunctival suffusion, severe calf myalgias, and epidemiologic exposure to contaminated water or animal urine, and initiate antibiotics immediately without waiting for laboratory confirmation. 1, 2

Clinical Diagnostic Criteria

The diagnosis should be suspected when patients present with:

• Fever (usually ≥39°C) with chills - present in nearly all cases 1, 3
• Conjunctival suffusion - a highly suggestive pathognomonic sign that distinguishes leptospirosis from other febrile illnesses 1, 3
• Severe diffuse myalgias, especially in the calves - this specific distribution is characteristic 1, 3
• Headache - commonly accompanies the acute presentation 1, 3
• Jaundice - indicates progression to severe disease (Weil's disease) and is an independent predictor of severity 1, 3

Epidemiologic Risk Factors to Elicit

A careful history must identify exposure risks:

• Occupational exposure to animals (agricultural workers, veterinarians) or contaminated water 4
• Recreational water activities in fresh water sources (swimming, wading, adventure sports) 4, 5
• Recent travel to endemic areas, particularly Southeast Asia or tropical regions 6
• Exposure to rats, cattle, pigs, dogs or their urine 4, 7
• Flooding or excess rainfall in the preceding 1-2 weeks 4, 8

Laboratory Testing Approach

Initial Laboratory Findings (Non-Specific but Supportive)

• Thrombocytopenia (platelets <140 G/L) - present in 65.5% of cases 3
• Leukocytosis with polymorphonuclear predominance 1
• Elevated bilirubin with only mild transaminase elevation - this pattern distinguishes leptospirosis from viral hepatitis 1, 2
• Proteinuria and hematuria on urinalysis 1
• Elevated creatinine indicating renal involvement 1, 3

Confirmatory Testing (Do Not Delay Treatment)

Serology is the most common confirmatory method but takes days to weeks:

• IgM titers >1:320 are diagnostic of leptospirosis 1, 2
• IgM titers 1:80-1:160 suggest early infection 1
• Convalescent serology (>10 days after symptom onset) confirms diagnosis retrospectively 1
• Earliest positive serologies appear 6-10 days after symptom onset 2

Blood cultures should be obtained if possible:

• Draw within the first 5 days of illness, before antibiotics 1, 2
• Only obtain if this causes no significant delay (<45 minutes) 2
• Cultures are most likely positive during the septicemic phase (days 1-7) 1

Molecular testing (NAAT) has rapid turnaround (1-2 hours) but availability is limited 1

Critical Pitfall: Misdiagnosis as Viral Hepatitis

Do not misdiagnose leptospirosis as viral hepatitis in patients with fever and jaundice - the key distinguishing features are:

• Leptospirosis shows high bilirubin with only mild transaminase elevation 1, 2
• Presence of conjunctival suffusion, severe myalgias, and renal dysfunction point to leptospirosis 1, 2
• Epidemiologic exposure history is critical 1

Severity Assessment and Classification

Classify patients into two categories:

Mild to Moderate Leptospirosis

• Flu-like symptoms without organ failure 1
• Most common presentation 1
• Hospitalize if systemic signs of infection are present, even without severe disease criteria 1

Severe Leptospirosis (Weil's Disease)

Occurs in 5-10% of cases and is characterized by: 1, 7

• Jaundice with hemorrhagic manifestations 2, 3
• Acute renal failure (creatinine >500 μmol/L in severe cases) 3
• Pulmonary hemorrhage or ARDS 3
• Cardiac involvement (myocarditis, pericarditis, arrhythmias) - an independent predictor of severity 3
• Meningitis or meningoencephalitis 3

Independent predictors of progression to severe disease are clinical jaundice (p=0.005) and cardiac damage on exam or ECG (p<0.02) - these should trigger immediate ICU consultation. 3

Treatment Initiation

Start antibiotics within the first hour of recognizing severe leptospirosis or septic shock, as each hour of delay increases mortality. 1, 2

Antibiotic Regimens

• Penicillin or doxycycline are the recommended first-line agents 1, 2
• Standard course is 7 days, extend to 10 days if slow clinical response 1, 2
• Treatment initiated after 4 days of symptoms may be less effective 1
• Complete the full antibiotic course even with clinical improvement - do not discontinue prematurely 2

Supportive Care for Severe Cases

• Fluid resuscitation targeting systolic BP >90 mmHg in adults 1, 2
• Monitor continuously for crepitations indicating fluid overload 1, 2
• Never leave septic patients alone - frequent clinical examinations are mandatory 1, 2
• ICU admission if persistent hypoperfusion despite initial resuscitation 2

Diagnostic Algorithm Summary

1. Suspect clinically based on fever + conjunctival suffusion + myalgias + exposure history
2. Obtain blood cultures if <45 minutes delay and within first 5 days
3. Send IgM serology but do not wait for results
4. Check CBC, CMP, urinalysis for supportive findings
5. Assess severity using jaundice and cardiac involvement as key predictors
6. Initiate antibiotics immediately (penicillin or doxycycline) without waiting for confirmation
7. Hospitalize moderate cases; ICU for severe cases