What are Faine's criteria for diagnosing leptospirosis?

Faine's Criteria for Diagnosing Leptospirosis

Faine's criteria is a clinical scoring system that combines epidemiological exposure history (Part A), clinical features (Part B), and laboratory findings (Part C) to diagnose leptospirosis when definitive testing is unavailable or delayed, with the modified version (2012) demonstrating 95% sensitivity and 57% specificity when validated against confirmatory testing. 1

Structure of Faine's Criteria

The scoring system consists of three parts that are added together, with a total score ≥26 points indicating probable leptospirosis: 2, 3

Part A: Epidemiological Factors (Maximum 10 points)

• Contact with contaminated animals (rats, cattle, pigs, dogs) or their urine 4, 5
• Exposure to soil or water contaminated with animal urine 6
• Occupational exposure (agricultural workers, especially in flooded fields or rice production areas) 6, 7
• Recreational water activities in fresh water sources 4, 6
• Recent flooding with water contact 4, 5
• Exposure history within 2-20 days prior to symptom onset 5

Part B: Clinical Features (Maximum 15 points)

• High fever (usually ≥39°C) with chills 4, 5
• Severe myalgias, especially in the calves 4, 5
• Headache 4, 5
• Conjunctival suffusion (highly suggestive physical finding) 4, 5, 7
• Muscle tenderness 7
• Jaundice (indicates severe disease/Weil's disease) 4, 5
• Signs of hemorrhage 5
• Hepatomegaly 5

Part C: Laboratory Findings (Maximum variable points)

• Leukocytosis with neutrophilia 4, 7
• Elevated erythrocyte sedimentation rate (ESR) 7
• Proteinuria and hematuria on urinalysis 8, 4
• Elevated bilirubin with mild elevation of transaminases (especially AST) 4, 7
• Alterations in renal function tests 4
• Modified Faine's criteria (2012) incorporates rapid immunochromatographic assay (IgM) results in Part C, improving practical utility 1

Diagnostic Performance

The modified Faine's criteria demonstrates: 1

• Sensitivity: 95.45% when using MAT ≥1:400 and/or PCR as reference standard
• Specificity: 56.86%
• Positive predictive value: 58.88%
• Negative predictive value: 95.08% (most clinically useful feature)

When using only immunochromatographic assay (IgM) in Part C: 1

• Sensitivity: 89.39%
• Specificity: 58.82%
• Negative predictive value: 89.55%

Other studies show similar performance with sensitivity of 81-89% and specificity of 73-80% 3, 9

Clinical Application and Limitations

The high negative predictive value (95-99%) makes Faine's criteria most valuable for excluding leptospirosis during the early phase of illness when serology may still be negative. 3, 9

Key considerations: 2, 3, 7

• Only 7 of 13 confirmed leptospirosis cases were positive by original Faine's criteria, but all 13 were positive using modified criteria 2
• The criteria has moderate sensitivity and specificity but significantly high positive predictive value (31-41%) considering the non-specific nature of symptoms 3, 9
• Most useful in resource-poor settings where definitive testing (MAT, PCR) is unavailable or delayed 1
• Do not wait for serological confirmation before starting antibiotics, as serology is often negative in the first week 5

Integration with Definitive Testing

While Faine's criteria guides clinical decision-making: 4, 5

• IgM titers >1:320 are diagnostic of leptospirosis
• IgM titers of 1:80-1:160 suggest early infection
• Convalescent serology (>10 days after symptom onset) with MAT confirms diagnosis
• Blood cultures should be obtained in the first 5 days before antibiotics when possible
• Treatment should be initiated immediately upon clinical suspicion without waiting for confirmation, as delay increases mortality 5