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Clinical Pearls & Morning Reports


Published May 31, 2017

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What are risk factors for leptospirosis and how is it transmitted?

Leptospirosis is endemic worldwide, although it is most prevalent in tropical and rural environments. In the United States, leptospirosis is most commonly diagnosed among travelers who have returned from areas in which the disease is endemic (particularly Southeast Asia, Central America, and the Caribbean) and among residents of tropical or semitropical regions, with Hawaii having the highest incidence. Read the latest Clinical Problem-Solving article

Clinical Pearls

Q. What are risk factors for leptospirosis and how is it transmitted?

A. The most important reservoirs of leptospirosis are rodents and small mammals, and contact with their urine, often through contaminated water, is the primary route of transmission. Leptospira enters the body through direct cutaneous or mucosal transmission or by aerosolization. Water exposure is a key risk, both domestically and abroad, with multiple reported outbreaks associated with adventure races and ecotourism. A risk factor that is less well known is residence in a city that has a large population of rodents; one Baltimore study showed that 65% of live-trapped rats had antibodies to L. interrogans. Multiple cases of urban leptospirosis infection, in which the presumed mechanism of infection is injury sustained in a rat-infested alleyway or home, have been documented.

Q. Is leptospirosis difficult to diagnosis?

A. The diagnosis of leptospirosis can be challenging to confirm. The organism requires specialized culture mediums and grows over a period of weeks. Serologic testing is often negative early in the course of the disease. Polymerase-chain-reaction–based nucleic acid amplification testing of blood, urine, or cerebrospinal fluid is much more sensitive than culturing and can be performed early in the course of the disease, but such testing is not widely available. Given these limitations, most diagnoses are still confirmed by serologic testing.

Morning Report Questions

Q: What are some of the clinical manifestations of leptospirosis?

A: Leptospirosis has a broad range of manifestations, from subclinical illness or mild self-limited disease (approximately 90% of infections) to Weil’s syndrome, which is characterized by renal failure, jaundice, and hemorrhage and has a 5 to 15% mortality rate. Symptoms develop after an incubation period of 5 to 14 days. Mild infections are often indistinguishable from other febrile illnesses. Cardinal features of severe leptospirosis include nonoliguric renal failure and marked hyperbilirubinemia (a bilirubin level of up to 30 to 40 mg per deciliter [512 to 684 μmol per liter] in some cases). The spectrum of pulmonary involvement is broad, but the most serious manifestations are diffuse alveolar hemorrhage and the acute respiratory distress syndrome. Common symptoms are conjunctival suffusion (extreme conjunctival redness without exudate), muscle tenderness, and aseptic meningitis. Nonspecific symptoms, including fever, gastrointestinal upset, headache, cough, and pharyngitis, are also common. Infection with icterohemorrhagiae serogroups has been reported to be associated with an increased risk of severe disease or death.

Q: How is leptospirosis treated?

A: Controversy exists over whether antibiotics decrease the severity of leptospirosis. A review of seven randomized trials showed that the evidence in favor of or against antibiotic therapy in leptospirosis is insufficient; the duration of the disease appeared to be shorter among patients treated with antibiotics than among those who did not receive antibiotics, but the differences were not significant. In a retrospective observational study, delayed initiation of antibiotics (by 2 days or more) was associated with more severe disease. Guidelines and expert opinion support prompt treatment with antibiotics in suspected and confirmed cases. Oral doxycycline is used to treat mild disease, and intravenous penicillin is used to treat severe disease, although a trial that compared ceftriaxone (1 g daily) with penicillin (1.5 million units every 6 hours) for 7 days showed no significant difference in the time to resolution of fever.

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