How is leptospirosis diagnosed?

How to Diagnose Leptospirosis

Diagnose leptospirosis through a combination of serologic testing (IgM ELISA and microscopic agglutination test) after 6-10 days of symptoms, or blood/CSF cultures within the first 5 days before antibiotics, guided by clinical presentation of fever, myalgia (especially calves), and conjunctival suffusion in patients with water or animal urine exposure. 1

Clinical Suspicion and Timing

Suspect leptospirosis in patients presenting with:

• Fever, headache, chills, and myalgia (particularly calf muscles) 1
• Conjunctival suffusion (highly suggestive finding) 1
• Biphasic illness pattern: initial bacteremic phase with flu-like symptoms (4-7 days), followed 1-3 days later by immune phase with fever, hepatorenal syndrome, and hemorrhage 1
• Exposure history: contact with urine-contaminated water, recreational water sports, occupational animal exposure, or flooding 1

Diagnostic Algorithm by Timing

Early Disease (First 5 Days of Symptoms)

Blood and CSF cultures are the primary diagnostic method during the bacteremic phase 1:

• Collect aerobic blood cultures before antibiotics 1
• Keep blood cultures at room temperature prior to dispatch to reference laboratory 1
• CSF cultures can also be obtained if meningeal signs present 1
• Urine is NOT a suitable sample for isolation of leptospira 1

After 6-10 Days of Symptoms

Serologic testing becomes the primary diagnostic method 1:

Initial serology:

• IgM ELISA is the rapid screening test 1
• IgM titer ≥1:320 is considered suggestive of leptospirosis 1
• Titers of 1:80 to 1:160 are consistent with early infection but may represent cross-reactions 1

Confirmatory testing:

• Convalescent serology >10 days after symptom onset should include both IgM ELISA and microscopic agglutination test (MAT) 1
• MAT is the gold standard serologic test 2, 3
• Earliest positive serology appears 6-10 days after onset of symptoms 1

Supportive Laboratory Findings

Initial investigations are non-specific but may show 1:

• Urinalysis: proteinuria and hematuria 1
• Hematology: polymorphonuclear leukocytosis, thrombocytopenia, anemia if hemorrhage occurred 1
• Coagulation: often normal despite bleeding (due to capillary fragility) 1
• Biochemistry: renal failure, high bilirubin with mild transaminase elevation 1

Case Classification

Probable case 1:

• Clinically compatible presentation (fever, headache, chills, myalgia, conjunctival suffusion)
• Supportive serology: Leptospira agglutination titer ≥1:200 in one or more serum specimens

Confirmed case 1:

• Isolation of Leptospira from clinical specimen, OR
• Fourfold or greater increase in Leptospira agglutination titer between acute and convalescent sera obtained ≥2 weeks apart, OR
• Demonstration of Leptospira by immunofluorescence in clinical specimen

Critical Pitfalls to Avoid

• Do not wait for laboratory confirmation to initiate treatment given the non-specific nature of initial investigations and potential for rapid deterioration 1
• Do not send urine for culture as it is not suitable for leptospira isolation 1
• Do not store blood cultures in refrigerator—maintain at room temperature before sending to reference lab 1
• Do not rely on single acute-phase serology—convalescent titers are needed for confirmation 1
• Recognize that severe disease (Weil's disease) may not respond to antibiotics as it is immunologically mediated 1

Modern Diagnostic Considerations

While not widely available, PCR amplification of bacterial DNA from blood during the first week can provide rapid diagnosis 4, and loop-mediated isothermal amplification (LAMP) and CRISPR-based approaches represent emerging diagnostic technologies 2.