What are the clinical and biochemical features of leptospirosis?

Clinical and Biochemical Features of Leptospirosis

Leptospirosis presents with a characteristic biphasic illness pattern, ranging from mild flu-like symptoms to severe multi-organ failure (Weil's disease), with conjunctival suffusion being a highly suggestive clinical sign. 1

Clinical Presentation

Disease Spectrum and Phases

Leptospirosis follows a biphasic course consisting of:

• Bacteremic phase (4-7 days): Flu-like symptoms including fever (present in 96-100% of cases), myalgia (particularly calf muscles in 48-92% of cases), headache (41-75%), and anorexia 1, 2, 3

• Immune phase (1-3 days later): Characterized by recurrent fever, myalgia, hepatorenal syndrome, and hemorrhagic manifestations 1

Key Clinical Features

Highly suggestive findings:

• Conjunctival suffusion - a pathognomonic sign when present 1
• Calf muscle tenderness - distinguishes leptospirosis from other acute febrile illnesses 4
• Conjunctival congestion 4

Common manifestations by frequency:

• Fever: 96-100% 1, 2, 3
• Jaundice: 17.6-94.5% (higher in severe cases) 2, 3
• Myalgia: 48-92% 2, 3, 5
• Headache: 41-75% 2, 3, 5
• Vomiting/GI upset: 53-72% 3, 5
• Oliguria: 29.4% 2
• Respiratory distress: 25.5-48% 2, 5

Severe Disease (Weil's Disease)

Characterized by the triad of:

• Hemorrhagic manifestations (9.8-35.8% of cases) 1, 2, 3
• Jaundice (hepatic dysfunction)
• Hepatorenal failure (acute kidney injury in 87% of hospitalized patients) 3

Additional severe complications:

• Pulmonary hemorrhage (62.1% in ICU patients, mortality 35%) 6
• Myocarditis (75.9% in ICU patients) 6
• Altered sensorium/encephalopathy (21.6%) 2
• Hypotension/shock (15.7%) 2

Biochemical and Laboratory Features

Hematologic Abnormalities

• Thrombocytopenia: Platelet count <100,000/mm³ in 74.3% of cases 1, 3
• Polymorphonuclear leucocytosis (not leukopenia - this distinguishes it from dengue) 1, 4
• Neutrophilia - independent risk factor for severe disease 7, 4
• Anemia (if significant hemorrhage has occurred) 1

Renal Function

• Acute kidney injury: Present in 87% of hospitalized patients 3
• Proteinuria and hematuria on urinalysis (42.9% have hematuria) 1, 3
• Elevated creatinine indicating renal failure 1

Hepatic Function

• High bilirubin with mild elevation of transaminases - this pattern is characteristic 1
• Elevated aspartate aminotransferase (AST) 4
• Jaundice in 74.5% of patients on examination 2

Other Laboratory Findings

• Elevated ESR (erythrocyte sedimentation rate) 4
• Elevated creatine phosphokinase (CPK) 2
• Normal coagulation studies despite bleeding - bleeding is due to capillary fragility, not coagulopathy 1
• Elevated LDH 8

Clinical Phenotypes

Recent research has identified three distinct clinical phenotypes 7:

1. Mild leptospirosis (45.3%): Less organ dysfunction, shorter hospital stays
2. Respiratory leptospirosis (29.5%): Hemoptysis, respiratory and circulatory failure
3. Hepato-renal leptospirosis (25.3%): Worst liver and kidney dysfunction

In ICU settings, four phenotypes emerge with isolated pulmonary hemorrhage and multi-organ failure carrying the highest mortality (35% and 25.6% respectively) 6.

Diagnostic Considerations

Clinical Predictors

Epidemiological clues:

• Contact with contaminated water or animal urine 1, 4
• Drinking unboiled water 4
• Occupational exposure (farming, veterinary work) or recreational water sports 1
• Recent flooding 1

Physical Examination Findings

• Splenomegaly: Likelihood ratio 5.1-13.6 for malaria, but also present in 72.5% of leptospirosis cases 2
• Hepatosplenomegaly: 72.5% 2
• Tachypnea: 52.9% 2

Important Caveats

• Initial investigations are non-specific - treatment should begin on clinical suspicion alone 1
• Serological confirmation appears 6-10 days after symptom onset; IgM titre >1:320 is suggestive 1
• Respiratory symptoms and chest X-ray abnormalities occur in 52-63% of cases, with multiple nodular densities being the most common pattern (42%) 5
• Dyspnea and elevated neutrophil counts are independent risk factors for progression to severe disease 7
• Overall mortality ranges from 4.3-17.2%, but reaches 35% in respiratory phenotypes 5, 6