Leptospirosis is an infection with spirochetes from the genus Leptospira. Infections are most commonly caused by Leptospira interrogans, of which more than 200 serovars infect humans. People become infected by exposure to animal urine or urine-contaminated surface water. Leptospira penetrate intact mucous membranes and abraded skin and disseminate widely via the bloodstream. Symptoms develop 7 to 12 days after exposure. Most patients have an abrupt onset of a self-limited, 4- to 7-day anicteric illness characterized by fever, headache, myalgias, chills, cough, chest pain, neck stiffness, and/or prostration (Table 164.1). An estimated 10% of patients will present with jaundice, hemorrhage, renal failure, and/or neurologic dysfunction (Weil's disease). The major clinical manifestations of disease result from infection of capillary endothelial cells leading to vasculitis (Table 164.2).

Classically, leptospirosis has been considered a biphasic illness. However, many patients with mild disease will not have symptoms of the secondary “immune” phase of illness, and patients with very severe disease will have a relentless progression from onset of illness to jaundice, renal failure, hemorrhage, hypotension, and coma. The illness is biphasic in about half of patients, with relapse occuring approximately 1 week after resolution of the initial febrile illness. A late complication is anterior uveitis, seen in up to 10% of patients months to years after convalescence. Leptospirosis in pregnancy is associated with spontaneous abortion but children with congenitally acquired leptospirosis have not been described to have congenital anomalies.