Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Outbreak of Leptospirosis Among White-Water Rafters -- Costa Rica, 1996

On October 15, 1996, a physician notified the Illinois Department of Public Health about five patients with an unknown febrile illness who had returned from a white-water rafting trip on flooded rivers in Costa Rica during September 27-28, 1996. The five patients had been members of a white-water rafting expedition involving 26 rafters from five states, the District of Columbia, and Costa Rica. This report summarizes the findings of the multistate investigation conducted by the Illinois Department of Public Health and by CDC in collaboration with the Ministry of Health of Costa Rica. The findings implicated leptospirosis as the cause of disease and contaminated river water as the probable source of illness.

A participant list was obtained from the trip organizer. Investigators interviewed all 26 trip participants to assess symptoms and potential environmental and behavioral risk factors, and reviewed medical records of those who sought medical attention. Based on the preliminary review of information available to investigators, the differential diagnoses included dengue fever and leptospirosis. A case of acute illness in a rafter was defined as fever associated with rigors, headache, and myalgia, with onset during September 27-November 1, 1996. Serum specimens were analyzed for evidence of dengue fever by IgM enzyme-linked immunosorbent assay (ELISA), and for leptospirosis by the microscopic agglutination test (MAT) and Leptospira IgM ELISA. Laboratory-confirmed leptospirosis was defined as a fourfold rise in MAT titers between acute- and convalescent-phase serum specimens against Leptospira serovars. A probable positive result was defined as an agglutination titer of greater than or equal to 200 to one or more Leptospira serovars in at least one serum specimen.

Of the 26 rafters (median age: 34 years), nine (34.6%) had illness that met the case definition. The median incubation period (measured from the first day of rafting) was 12 days. Symptoms were self-limited in three case-patients and six were placed on antimicrobial therapy, of whom two were hospitalized; all recovered. Risk for illness was associated with reporting having ingested river water (nine of 18 versus none of eight; relative risk {RR}=8.7, 95% confidence interval {CI}=1.5-) and being submerged under water after falling into the river while rafting (nine of 20 versus none of six; RR=6.0, 95% CI=1.1-).

Sixteen persons submitted at least one serum specimen (eight case-patients and eight noncase-patients), and all were negative for anti-dengue IgM. Seven case-patients submitted both acute- and convalescent-phase serum specimens; of these, two persons were positive for leptospirosis by MAT and by IgM ELISA on convalescent testing. Leptospirosis was considered probable in three paired serum samples by MAT, all of which were IgM ELISA-positive on convalescent testing; two were negative by MAT and by IgM ELISA testing. One case-patient submitted only an acute-phase serum specimen, which was negative by both MAT and IgM ELISA. Analysis of additional blood specimens obtained from seven case-patients documented slightly elevated liver function tests in all seven patients and thrombocytopenia in three patients.

Reported by: BE Reisberg, MD, R Wurtz, MD, Northwestern Univ Medical School, Chicago; P Diaz, MD, Chicago Dept of Public Health; B Francis, MD, State Epidemiologist, Illinois Dept of Public Health. P Zakowski, MD, Cedar-Sinai Medical Center, Los Angeles; S Fannin, MD, Los Angeles County Health Dept, Los Angeles; Stanislaus County Health Dept, Modesto; San Joaquin County Health Dept, Stockton; D Sesline, DVM, S Waterman, MD, State Epidemiologist, California Dept of Health Svcs. R Sanderson, MA, Hillsborough County Health Dept, Tampa; Florida Dept of Health. T McChesney, DVM, State Epidemiologist, Arkansas Dept of Health. R Boddie, MSN, M Levy, MD, District Epidemiologist, District of Columbia Commission of Public Health. G Miller, Jr, MD, State Epidemiologist, Virginia State Health Dept. G Herrera, MD, Ministry of Health, San Jose, Costa Rica. State Br, Div of Applied Public Health Training (proposed), Div of Prevention Research and Analytic Methods (proposed), Epidemiology Program Office; Dengue Br, and Meningitis and Special Pathogens Br, Div of Bacterial and Mycotic Diseases; Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The findings in this investigation indicated that leptospirosis was the cause of the rafters' acute febrile illness; contaminated river water was the most likely source of the organisms based on the known epidemiology of Leptospirosis and the epidemiologic findings. Leptospirosis is a widespread zoonosis that is endemic in the tropics and infects a variety of wild and domestic animals that excrete the organism in their urine. Leptospira proliferate in fresh water, damp soil, vegetation, and mud. The occurrence of flooding after heavy rainfall facilitates the spread of the organism because, as water saturates the environment, Leptospira present in soil pass directly into surface waters (1). Human infection occurs through exposure to water or soil contaminated by infected animal urine and has been associated with canoeing, wading, and swimming in contaminated lakes and rivers (2,3). A large epidemic of leptospirosis associated with pulmonary hemorrhage occurred in 1995 in Nicaragua following widespread flooding and affected approximately 2000 persons (4,5).

Leptospira may enter the body through cut or abraded skin, mucous membranes, and conjunctivae. The acute generalized illness associated with infection may mimic other tropical diseases (e.g., dengue fever, malaria, and typhus) (1,6), and common symptoms include fever, chills, myalgia, nausea, diarrhea, and conjunctivitis. Manifestations of severe disease may include jaundice, renal failure, hemorrhage, and hemodynamic collapse (7). The organism may be isolated from samples of blood and cerebrospinal fluid obtained during the first 10 days of illness, and in the urine following the first week of illness. The MAT -- the standard for serologic diagnosis of leptospirosis and the most reliable test -- is not widely available in the United States (8). Testing for leptospirosis using MAT is available at CDC's Division of Bacterial and Mycotic Diseases laboratory, National Center for Infectious Diseases, through referral by state health departments.

Treatment with antimicrobial agents (e.g., penicillin, amoxicillin, or doxycycline) should be initiated early in the course of disease, and intravenous penicillin or ampicillin should be used for persons with severe manifestations. Supportive therapy is indicated for treating dehydration, hypotension, hemorrhage, and renal failure (9). Oral doxycycline (200 mg weekly) may provide effective chemoprophylaxis for persons with short-term exposure in environments associated with increased risk for infection (10). Persons participating in recreational water activities in areas where leptospirosis is endemic may be at increased risk for the disease, particularly during periods of flooding, and should consider preventive measures such as wearing protective clothing and minimizing contact with potentially contaminated water (1). Physicians should ask about a travel history and consider leptospirosis in the differential diagnosis for persons with a recent history of travel to areas with endemic disease.


  1. Faine S, ed. Guidelines for the control of leptospirosis. Geneva, Switzerland: World Health Organization, 1982; WHO offset publication no. 67.

  2. Anderson DC, Folland DS, Fox MD, Patton CM, Kaufmann AF. Leptospirosis: a common-source outbreak due to leptospires of the grippotyphosa serogroup. Am J Epidemiol 1978;107:538-44.

  3. Jackson LA, Kaufmann AF, Adams WG, et al. Outbreak of leptospirosis associated with swimming. Pediatr Infect Dis J 1993;12:48-54.

  4. CDC. Outbreak of acute febrile illness and pulmonary hemorrhage -- Nicaragua, 1995. MMWR 1995;44:841-3.

  5. Zaki SR, Shieh WJ, Epidemic Working Group at the Ministry of Health in Nicaragua. Leptospirosis associated with outbreak of acute febrile illness and pulmonary haemorrhage, Nicaragua, 1995 {Letter}. Lancet 1996;347:535-6.

  6. Farr RW. Leptospirosis. Clin Infect Dis 1995;21:1-8.

  7. Berman SJ, Tsai CC, Holmes K, Fresh JW, Watten RH. Sporadic anicteric leptospirosis in South Vietman: a study in 150 patients. Ann Intern Med 1973;79:167-73.

  8. Kaufmann AF, Weyant RS. Leptospiraceae. In: Murray PR, Baron EJ, Pfaller MA, Tenover FC, Yolken RH, eds. Manual of clinical microbiology. 6th ed. Washington, DC: American Society for Microbiology, 1995:621-5.

  9. Farrar WE. Leptospira species (Leptospirosis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases. 4th ed. New York: Churchhill Livingstone, 1995: 2137-41.

  10. Takafuji ET, Kirkpatrick JW, Miller RN, et al. An efficacy trial of doxycycline chemoprophylaxis against leptospirosis. N Engl J Med 1984;310:497-500.

Disclaimer   All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 09/19/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01