Microbiology and Epidemiology

Leptospires are spirochetal organisms that cause an important zoonosis with a broad spectrum of clinical manifestations.

• Rodents, particularly rats, are the most important reservoir, but leptospirosis affects almost all mammalian species. Transmission can occur during contact with urine, blood, or tissue from infected animals or, more commonly, during exposure to contaminated environments (e.g., during recreational water activities).
• Globally, there are ∼1 million severe cases each year, with a mean case-fatality rate of ∼10%.

Clinical Manifestations

After an average incubation period of 1-2 weeks, infection by Leptospira results in a subclinical infection, an undifferentiated febrile illness, or Weil's disease (the most severe form).

• Leptospirosis is a biphasic illness. The initial leptospiremic phase lasts 3-10 days and is characterized by fever; organisms can be cultured from blood during this phase. After another 3-10 days (the immune phase), symptoms resolve, and leptospires can be cultured from urine.
  • Nonspecific physical findings may include conjunctival suffusion, nonexudative pharyngeal injection, muscle tenderness, lymphadenopathy, crackles on lung auscultation, jaundice, hepatosplenomegaly, and a transient rash.
• Severe leptospirosis, often referred to as Weil's syndrome, encompasses the triad of hemorrhage, jaundice, and acute renal injury. Up to 50% of pts die of septic shock with multiorgan failure and/or severe bleeding in the lungs, GI and urogenital tracts, and skin. Altered mental status may reflect leptospiral meningitis.

Diagnosis

An appropriate exposure history combined with any of the protean manifestations of leptospirosis suggests the clinical diagnosis and guides confirmatory testing.

• Definitive diagnosis rests on demonstration of the organism by culture isolation (which takes weeks or months), on a positive PCR result, or on seroconversion or a ≥4-fold rise in antibody titer.
  • Leptospires can be cultured from blood and CSF during the first 7-10 days of illness.
  • Urine cultures are positive in the second week of illness.