Leptospirosis is a bacterial zoonotic infection caused by any of the serovarieties of the spirochetes from the Leptospira interrogans species. The geographic distribution is worldwide, but it is endemic in tropical climates and sporadic in temperate climates, and more common in summer and after floods (eg, after hurricane). It is carried primarily by amphibians, reptiles, and some mammals (rodents are the main source), and it may be passed to humans by direct contact with or aerosol inhalation of contaminated urine or body fluids.

Leptospirosis has protean manifestations. Initial symptoms include the onset of remittent fever, chills or rigors (shaking chills), myalgia, headache, low back pain, and conjunctivitis / uveitis. Conjunctival suffusion (conjunctival redness without inflammatory exudate) is a classic clinical sign. In 2 large case studies, it occurred in 20%-99% of infected patients. Some cases may also demonstrate a dry cough, nausea, vomiting, diarrhea, abdominal pain, and a pretibial rash of erythematous papules. The illness may progress to Weil disease, a more severe form, which includes jaundice, kidney and/or liver failure, meningitis, pneumonitis with hemoptysis, acute respiratory distress, hemorrhage, shock, and death. The mortality rate is about 40% for Weil disease and between 1%-5% overall.

Leptospirosis may be difficult to diagnose because its initial symptoms are similar to many other diseases, and some cases have few to no symptoms, but early diagnosis is crucial, as successful treatment should be started within the first 4 days of illness.

The incubation period of leptospirosis is usually 5-14 days, although it can range anywhere from 2-30 days. The bacteria are typically found in water, soil, or food contaminated with the urine of wild and domestic animals. It is transmitted by ingestion, inhalation, and direct contact with mucosal surfaces or broken skin. The infection can be transmitted person to person only by direct contact with contaminated urine and body fluids.

There is no vaccine against leptospirosis.

People at risk for leptospirosis include military personnel, veterinarians, dog and other pet owners, slaughterhouse and sewer workers, campers, swimmers, triathlon participants, waders, white water rafters, and dairy, cattle, and pig farmers.

Note: In 2023, New York City reported 24 cases leptospirosis, which is the highest number in a single year, and as of April 2024, 6 cases have been reported. These human leptospirosis infections have been associated with exposure to environments and materials contaminated with rat urine.