Outbreak of Acute Febrile Illness Among Athletes Participating in Triathlons—Wisconsin and Illinois, 1998 FREE

MMWR. 1998;47:585-588. 1 figure omitted

ON JULY 14, 1997, the Wisconsin Division of Health (WDOH) was notified by the City of Madison Health Department that three athletes were hospitalized with an acute febrile illness. The illness was characterized by fever, myalgia, and headache with illness onset on July 6, 7, and 10, respectively. One of these three athletes had acute renal failure. Two of the athletes had participated in a triathlon* held in Madison, Wisconsin, on July 5 (692 registered participants) and all three had participated in a June 21 triathlon in Springfield, Illinois (961 registered participants). Eighty persons were registered for both events. Leptospirosis was suspected by WDOH staff as a likely cause of the illness and CDC was notified. Acute-phase serum specimens from two of the three hospitalized athletes obtained 4 and 8 days following onset of fever have been tested at CDC for leptospirosis using the PanBio enzyme-linked immunosorbent assay (ELISA) IgM screening test (PanBio, Brisbane, Australia)†; one specimen tested positive. This report presents preliminary findings of an ongoing investigation to identify additional cases of acute febrile illness among athletes participating in these two triathlons and to determine the cause of the illness.

To identify additional cases of febrile illness, triathlon participant lists were obtained from the race organizers; athletes from 44 states participated in at least one of the two events. A telephone survey of participants identified additional athletes with unexplained febrile illness. On July 17, CDC issued an advisory about the probable leptospirosis outbreak to increase awareness among health-care providers, athletes who participated in the Wisconsin and Illinois triathlons, and residents of the communities in which these events were held, and to request such illnesses be reported to CDC and state and local health departments.

Through July 20, a total of 639 triathlon participants from 39 states had been interviewed by telephone using a standardized questionnaire. Interviews have been completed for 588 (61%) of the Illinois participants and for 126 (18%) of the Wisconsin participants. A case was defined as onset of fever during June 21-July 20 in a triathlon participant that was associated with at least two of the following symptoms or signs: chills, headache, myalgia, diarrhea, eye pain, or red eyes. Seventy-four (12%) participants interviewed had an illness that met the case definition. The median age of these case-patients was 36 years (range: 15-80 years); 80% were male. Case-patients were similar in age and sex to athletes who were not ill. Among case-patients, symptoms and signs of illness were chills (89%), headache (77%), myalgia (73%), diarrhea (58%), eye pain (43%), and red eyes (26%). Fifty-four (73%) sought medical care; 21 (39%) of those were hospitalized. Among hospitalized patients, two had acute renal failure, two had abdominal surgery for suspected acute abdomen, and two had neurologic illnesses; one had suspected leptospirosis diagnosed.

Among the 74 case-patients, 64 (86%), four (5%), and six (8%) participated in the Illinois triathlon, the Wisconsin triathlon, or both, respectively. Signs and symptoms of illness did not differ significantly between athletes who participated exclusively in either the Illinois or Wisconsin triathlons (two-tailed Fisher exact; all p >0.10). Acute-phase serum samples obtained from an additional 16 case-patients identified as a result of the investigation have been tested at CDC for leptospirosis using Pan-Bio ELISA IgM. Specimens from two case-patients, both of whom participated in only the Illinois triathlon, tested positive. One of the 16 case-patients, who also participated in only the Illinois triathlon and whose serum specimen tested negative, had a cholecystectomy because of acute abdomen. No histopathologic evidence of cholecystitis was seen. Immunohistochemical staining of the gall bladder at CDC using rabbit polyclonal reference antiserum reactive with 16 different leptospiral strains was positive for leptospirosis.¹ Leptospiral antigens were seen as intact leptospira, thread-like filaments, and granular forms.² Paired, 2-week convalescent serum specimens are being obtained for the 18 patients (these 16 patients and the first two patients) whose acute-phase serum specimens (three positive and 15 negative) have been tested.

CDC in collaboration with state and local health departments is continuing to conduct epidemiologic, laboratory, and environmental investigations to characterize further this outbreak. The objectives of these investigations are to identify additional cases, to determine the etiology of illness among athletes who participated in triathlons in both Illinois and Wisconsin, to identify the source and mode of transmission, and to develop prevention and control measures.

Wisconsin Outbreak Investigation Team, Wisconsin Div of Health; City of Madison Health Dept. B Davis, Springfield Dept of Public Health, Springfield; Illinois Outbreak Investigation Team, Illinois Dept of Public Health. Council of State and Territorial Epidemiologists, Atlanta, Georgia. Infectious Disease Pathology Activity, Div of Viral and Rickettsial Diseases, and Meningitis and Special Pathogens Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and EIS officers, CDC.

The clinical signs and symptoms of illness among athletes meeting the case definition, the serologic and immunohistochemical testing, and the epidemiologic association with prolonged water exposure (1.5-mile lake swim) among these athletes suggest that leptospirosis, a water-borne disease, most likely is the cause of this outbreak. Because the signs and symptoms of leptospirosis are nonspecific, the case definition was purposefully broad and, as a result, may be detecting illness attributable to other causes. Although current epidemiologic data suggest that an environmental exposure probably occurred in the Illinois triathlon, additional laboratory and epidemiologic investigations are needed to exclude illness attributable to more than one exposure. As a precautionary measure, the city of Springfield and the Illinois Department of Public Health have issued an advisory not to swim, water-ski, or use personal watercraft at the site on the lake where the Illinois triathlon was held. Because only 18% of the Wisconsin participants had been interviewed, further interviews and laboratory evaluation of clinical specimens among athletes who participated in the Wisconsin triathlon are needed to evaluate the possibility of illness attributable to leptospirosis and to other pathogens.

Leptospirosis is a widespread zoonosis that is endemic in most temperate and tropical climates. Leptospires infect various animals that excrete the organism in their urine; the bacteria then persist in fresh water, damp soil, vegetation, and mud. Human infection occurs through exposure to water or soil contaminated by infected animal urine and has been associated with wading, swimming, and white-water rafting in contaminated lakes and rivers.^1,3- 5 Leptospires may enter the body through cut or abraded skin, mucous membranes, and conjunctivae. The incubation period is a few days to 4 weeks, and illness usually begins abruptly with fever, chills, rigors, myalgia, and headache, and may include conjunctivitis, abdominal pain, vomiting, diarrhea, and meningeal symptoms.⁶ Muscle pain, often severe, is most notable in the calf and lumbar areas. Skin rashes may occur. Leptospirosis can be a bi-phasic disease with an acute septicemic phase and a secondary phase of severe disease characterized by jaundice, renal failure, hemorrhage, or 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 microagglutination test (MAT), the standard for serologic diagnosis of leptospirosis, is time-consuming and difficult to perform.⁸ Therefore, the Pan-Bio ELISA is being used as a screening test in this investigation; serum specimens positive by Pan-Bio ELISA are being confirmed by MAT.

Mild infections can be treated with oral doxycycline; patients requiring hospitalization should be treated with intravenous penicillin.⁶ Additional information is available from CDC, telephone (888) 688-2732 ([888] OUTBREAK), on the World-Wide Web site, http://www.cdc.gov, or through state and local health departments.

*A triathlon is a race consisting of swimming, biking, and running competitions.

† Use of trade names and commercial sources is for identification only and does not imply endorsement by CDC or the U.S. Department of Health and Human Services.

MMWR. 1998;47:673-676

SINCE JULY 14, 1998, the Illinois Department of Health, the Wisconsin Department of Health, the U.S. Department of Agriculture (USDA), and CDC, in collaboration with other state and local health departments, have been investigating an outbreak of acute febrile illness among athletes from 44 states and seven countries who participated in triathlons* in Springfield, Illinois, on June 21, 1998, and in Madison, Wisconsin, on July 5, 1998.¹ Initial testing at CDC of specimens from four athletes identified leptospirosis as the illness in all four.¹ This report updates the ongoing investigation of this outbreak through August 13, which indicates that Leptospira was the etiologic agent for illness in athletes and in persons with occupational or recreational exposure to Lake Springfield, where the event was held in Illinois.

To identify cases of febrile illness, a standardized telephone survey was conducted of athletes who participated in the event in Illinois, the event in Wisconsin, or both events. Including late registrants and excluding preregistrants who did not participate in either event, respondents included 733 (95%) of 775 athletes who participated only in the Illinois event, 370 (67%) of 553 athletes who participated only in the Wisconsin event, and 91 (95%) of 96 athletes who participated in both events. A suspected case of leptospirosis was defined as onset of fever during June 21-August 13 in a triathlon participant that was associated with at least two of the following symptoms or signs: chills, headache, myalgia, diarrhea, eye pain, or red eyes.¹ Of the 1194 athletes surveyed, 110 (9%) who participated in one or both events described an illness meeting the case definition; no cases occurred after July 24. The median age of suspected case-patients was 35 years (range: 15-80 years); 76% were male. Ill athletes were similar in age and sex to athletes who were not ill. Of the 110, a total of 73 (66%) sought medical care; 23 (32%) of those were hospitalized.

Attack rates among respondents varied by triathlon site: 84 (11%) Illinois-only participants; 20 (5%) Wisconsin-only participants; and six (7%) athletes participating in both events. Compared with Wisconsin-only participants, Illinois-only participants were more likely to have had an illness meeting the case definition (relative risk [RR]=2.0; 95% confidence interval [CI]=1.3-4.0). Illinois-only case-patients also were more likely to have had chills, myalgias, or headache than Wisconsin-only case-patients (p <0.05); however, diarrhea was less common among Illinois-only case-patients. In addition, illness in Illinois-only case-patients had longer incubation periods (days from event to onset of fever: 14 days [Illinois-only] versus 7 days [Wisconsin-only]; p <0.01). Illinois-only case-patients were more likely to seek medical care than Wisconsin-only case-patients (RR=1.8; 95% CI=1.2-2.8). All 23 hospitalized athletes participated in the Illinois triathlon; none of the athletes participating only in the Wisconsin event were hospitalized.

Laboratory evidence for leptospirosis was defined as (1) a positive result for Leptospira on screening IgM enzyme-linked immunosorbent assay (ELISA) with confirmatory testing by a single microagglutination test (MAT) titer of ≥400, or a four-fold or greater rise in MAT titer between acute-phase and convalescent serum specimens;² (2) a positive tissue immunohistochemical (IHC) stain using rabbit polyclonal reference antiserum reactive with 16 different leptospiral strains³; or (3) a positive culture. Acute-phase serum specimens have been tested for 374 of 871 athletes who participated in the Illinois triathlon; 70 of these specimens were obtained from the 90 athletes whose illness met the case definition. Acute-phase serum specimens from 30 (43%) of these 70 case-patients and serum specimens from three (1%) of 304 athletes who had illness not meeting the case definition tested positive by ELISA. Of the 30 case-patients with a positive ELISA, 24 tested positive by confirmatory MAT with highest titers to pathogenic Leptospira serovars grippotyphosa, bratislava, and djasiman. In comparison, acute-phase serum specimens have been tested for 70 of 553 athletes who participated in only the Wisconsin triathlon, including 10 specimens from the 20 athletes whose illness met the case definition; none tested positive. Because serologic response can be delayed, convalescent specimens are required to interpret accurately serologic test results; paired, 2-week convalescent serum specimens are being obtained for all athletes whose acute-phase serum specimens have been tested. No positive cultures for Leptospira have been identified in either group of athletes.

On July 24, the Springfield and the Illinois departments of health issued a precautionary advisory not to swim, water ski, or use personal watercraft at Lake Springfield. To identify Springfield residents with only occupational or recreational exposure to Lake Springfield, the Springfield Department of Health initiated active and passive surveillance using the same case definition without specified time constraints. A total of 228 community case-patients in Springfield have been identified; 146 (64%) have had acute-phase serum specimens tested at CDC by ELISA. Specimens from five of these persons were positive by ELISA. Of these five, confirmatory testing by MAT has been performed for four; leptospirosis was confirmed in three case-patients, and confirmation for the fourth case-patient will require further testing of convalescent serum. Two hospitalized community residents who are suspected case-patients (serum specimens have yet to be tested) and who were treated with intravenous (IV) penicillin developed a Jarisch-Herxheimer reaction (a transient immunologic reaction following antibiotic treatment)⁴ requiring hemodynamic support.

CDC, in collaboration with USDA and state and local health departments, is continuing epidemiologic, laboratory, and environmental investigations of these outbreaks. The objectives are to (1) identify additional cases of leptospirosis among athletes and among occupational and recreational users of Lake Springfield, (2) determine the etiology of illness and identify the source and mode of transmission among athletes who participated in only the Wisconsin triathlon, and (3) develop prevention and control measures for both outbreaks.

Wisconsin Outbreak Investigation Team, Wisconsin Div of Health. Illinois Outbreak Investigation Team, Springfield Dept of Health and Illinois Dept of Public Health. Council of State and Territorial Epidemiologists, Atlanta, Georgia. Zoonotic Diseases Research Unit, Agriculture Research Svc, US Dept of Agriculture. Meningitis and Special Pathogens Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and EIS officers, CDC.

Leptospirosis is an acute febrile illness with a typical incubation period ranging from a few days to 4 weeks that usually begins abruptly with fever, chills, rigors, myalgia, and headache, and may include conjunctivitis, abdominal pain, vomiting, diarrhea, skin rashes, and meningeal symptoms.⁵ The acute septicemic phase can be followed by a secondary phase of severe disease characterized by aseptic meningitis, jaundice, renal failure, hemorrhage, or hemodynamic collapse. Mild infections can be treated with oral doxycycline; patients requiring hospitalization should be treated with IV penicillin.^1,5

Epidemiologic, serologic, and IHC staining evidence suggest that Leptospira was the etiologic agent causing disease among the athletes who participated in the Illinois triathlon. Similar illness and serologic confirmation among persons with occupational and recreational exposure to the same lake where the event was held support this theory. Athletes who participated in only the Wisconsin triathlon have demonstrated a different spectrum of symptoms and signs, have had a less severe illness, and have lacked serologic evidence for leptospirosis. However, additional serologic testing for leptospirosis among these athletes and additional testing for viral agents are needed.

Establishing an epidemiologic link between species of Leptospira obtained through environmental sampling (e.g., testing water, mud, and wild and domestic animals) and pathogenic serovars of Leptospira causing illness in humans in the same environments can be particularly difficult. Pathogenic Leptospira infect a variety of domestic and wild animals that subsequently excrete the organism in their urine. In temperate climates, both pathogenic and saprophytic Leptospira species can be found in fresh water, damp soil, vegetation, and mud, particularly during summer months.⁶ Therefore, no natural body of water can be expected to be free of Leptospira. Pathogenic and saprophytic Leptospira species obtained from environmental samples can be distinguished through a variety of tests, including molecular diagnostic testing;^6- 8 however, these techniques are difficult and time-consuming. The identification by culture or MAT of specific serovars causing leptospirosis in humans may facilitate identification of potential animal reservoirs (domestic and/or wild) of the environmental contamination.

Although leptospirosis has not been described among competitive athletes,⁹ recreational exposure to natural water sources is a common route of transmission.⁷ In the absence of a defined source of prior or continued contamination of Lake Springfield with pathogenic Leptospira, enhanced passive and active surveillance for symptoms and signs of illness of leptospirosis will be necessary to monitor the safety of recreational use of Lake Springfield.

Additional information regarding this outbreak is available from CDC, telephone (888) 688-2732 ([888] OUTBREAK); on the World-Wide Web site, http://www.cdc.gov/ncidod/dbmd/lepto.htm; or through state and local health departments.

*A triathlon is a race consisting of swimming, biking, and running competitions.