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Abstract & Commentary
Leptospirosis in Florida: Recreational Exposures Herald New Serovars and Highlight Environmental Impact
By Brian Blackburn, MD, Clinical Assistant Professor of Medicine, Division of Infectious Diseases and Geographic Medicine at Stanford University School of Medicine, is Associate Editor for Infectious Disease Alert.
Dr. Blackburn reports no financial relationships related to this field of study.
Synopsis: Forty-four (23%) of 192 adventure race participants in a 2005 Florida event developed suspected leptospirosis, with confirmatory serologic testing positive in 45% of the tested individuals. A unique serovar (related to species Leptospira noguchii) was isolated from one patient. Outbreaks of leptospirosis have become more commonly associated with adventure travel and sports activities, and highlight the effect the changing environment can have on infectious diseases.
Source: Stern EJ, et al. Outbreak of leptospirosis among adventure race participants in Florida, 2005. Clin Infect Dis. 2010;50:843-849.
Leptospirosis is a zoonosis caused by multiple serovars of bacteria in the genus Leptospira that are widely distributed in the tropics, as well as some subtropical and temperate areas. Although most commonly a self-limited febrile illness, a minority of patients develop severe leptospirosis (Weil's disease), which can result in jaundice, renal failure, or hemorrhagic manifestations.1 Many non-human mammals serve as the reservoir for this spirochete, which is excreted in the urine of such animals. As a result, infection is acquired predominantly in association with water and moist areas. Recently, infection has been increasingly associated with adventure travel and sporting activities, such as rafting, triathlons, and adventure races; outbreaks may be precipitated by flooding and heavy rainfall and can occur in areas not known to be endemic.2-4
In 2005, an adventure race with 200 participants took place near Tampa, Florida. The race involved paddling, cycling, trekking, and orienteering, and took place in a swamp; the race occurred two weeks after a hurricane passed over the area. Seventeen days after the race, the index case was admitted to a hospital in New York with fever, headache, and myalgias and, subsequently, several other racers developed similar illnesses, including a California racer who was diagnosed with leptospirosis based on a positive serologic test. An outbreak investigation conducted by the Centers for Disease Control and Prevention (CDC) and state/local health departments followed. For the investigation, a suspected case of leptospirosis was defined as a race participant who subsequently developed fever plus at least two classic symptoms or signs of leptospirosis (headache, myalgias, eye pain, conjunctival suffusion, jaundice, dark urine, or unusual bleeding). A suspected case was reclassified as laboratory confirmed if one of three tests was positive (leptospire culture, Dip-S-Tick [DST] test, or a serum microscopic agglutination test [MAT] result of > 400 in a single specimen, or a 4-fold increase in titers between two specimens).
Forty-four (23%) of the 192 interviewed racers met the definition for suspected leptospirosis, with a mean incubation period of about 13 days; three were hospitalized and none died. Cultures were attempted on the blood and urine of four patients, one of whom was positive for a novel serovar of species Leptospira noguchii. Fourteen (45%) of the 31 suspected cases who submitted serum samples were confirmed by laboratory testing. The most common signs and symptoms were fever (100%), headache (91%), chills (69%), sweats (68%), muscle/joint pain (68%), and eye pain or photophobia (39%). Factors significantly associated with leptospirosis included swallowing river or swamp water, eating wet food, and submersion in water. Severe cuts on the legs and wearing shorts were not statistically associated with infection.
Transmission of leptospirosis is perpetuated by environments that bring humans and animals into contact, especially those that are moist or contain bodies of freshwater. Although most common in the tropics, transmission does occur in temperate areas; in the United States, transmission is most common in Hawaii, and is also seen in the Pacific and southern states.1 Outbreaks of leptospirosis have been increasingly recognized, including during triathlons in the U.S. Midwest and during an eco-challenge multi-sport race in Malaysian Borneo.2-4 This outbreak of leptospirosis in Florida was similar in many ways to past outbreaks, with patients demonstrating many classic signs and symptoms, a relatively high attack rate, and an incubation period of about two weeks. Not surprisingly, the risk factors associated with infection included ingesting or being submerged in water. Although leptospirosis can be transmitted by many routes (including through mucous membranes, broken skin, and possibly aerosols), most outbreak investigations seem to indicate that infection is most strongly associated with ingestion of water, perhaps reflecting the large inoculum that results from this exposure.1
Climate change can affect the epidemiological environment in many ways, and areas that receive increased rainfall as a result of climate change can become better suited to transmission of infectious diseases such as leptospirosis.5,6 The passage of Hurricane Wilma over the race area two weeks before the event resulted in heavy rainfall and flooding, and likely contributed to the outbreak. The observed high attack rate was likely in part because of this environmental occurrence, as well as due to the race's location in a swamp. Many outbreaks have heralded the discovery of new endemic areas for infectious diseases and, in this case, the discovery of new infectious agents themselves. With leptospirosis outbreaks related to recreational exposures becoming more common, chemoprophylaxis should be considered for high-risk events. Doxycycline has been shown to be effective both for pre-exposure and post-exposure prophylaxis for leptospirosis, and should be a consideration for events that place participants at high risk of this infection.1,7,8