Waterborne Infectious Disease Outbreaks: Cryptosporidiosis & Leptospirosis

Special Coverage

Two recently reported outbreaks document the potential hazards of recreational water exposure. Both are reported by the Centers for Disease Control; the first describes an outbreak of cryptosporidiosis,1 and the second an outbreak of leptospirosis.2,3 In 1994, visitors to a state park in New Jersey began to experience diarrhea. The CDC, along with the New Jersey Department of Health investigated the extent and type of illness, the etiology, and the risk factors. Of those who visited the park and had diarrhea, 11% had laboratory-confirmed cryptosporidiosis. The illness in laboratory-confirmed cases consisted of 5-6 diarrheal stools per day, abdominal cramps (100%), nausea (94%), fever higher than 101°F (44%), headache (90%), vomiting (66%), and myalgias and arthralgias (58-41%). The median duration of illness was 11 days. Testing for other enteric pathogens was negative except for a few cases of concomitant Giardia lamblia infection. The strongest risk factor was contact with lake water, with duration and intensity of exposure (e.g., swallowing of water) increasing risk. The attack rate ranged from 21% for persons with single visits to the park to 61% for person with multiple visits. Based on the number of visitors to the park during the outbreak, which lasted over a month, at least 2000 persons became ill. The investigation determined that the most likely sources for cryptosporidium were a septic-tank backup and overflow that washed into the lake following heavy rainfall, swimming by children in diapers, documented fecal accidents in the water, and washing diapers in the lake.

Investigation of the second waterborne outbreak is ongoing. In mid-July of 1998, the Wisconsin Division of Health was notified that three athletes had been hospitalized with an acute febrile illness.2 The athletes had participated in triathlons in Springfield, IL, in late June and Madison, WI, in early July. Their illness was characterized by fever, myalgias, and headache. One of the three athletes had an acute phase serum positive for leptospirosis. Based on this finding, the CDC interviewed as many athletes as possible who had participated in either or both of the two triathlons. They have interviewed 370 of 553 (67%) persons in the Wisconsin event, 733 of 775 (95%) in the Illinois event, and 91 of 96 (95%) in both events.3 Of the 1194 athletes interviewed, 110 (9%) experienced an illness that met the case definition. Signs and symptoms among a subset of these were chills (89%), headache (77%), myalgias (73%), diarrhea (58%), eye pain (43%), and red eyes (26%).2 Seventy-three (66%) had sought medical care and 23 (32%) of these were hospitalized. Of hospitalized patients, two had abdominal surgery for a suspected acute abdomen, two had neurologic illness, and two had acute renal failure. One of the persons who had surgery had leptospira antigen documented in their gall bladder. An initial analysis of sera from 16 patients with illness yielded two positive for leptospira. Based on the combination of a compatible clinical syndrome, positive serology and antigen detection, and prolonged water exposure during the 1.5 mile lake swim, a Leptospira sp. was the most likely etiologic agent.

Additional analysis of participant interviews and leptospira serology indicated that only the Illinois triathlon was associated with leptospirosis.3 Wisconsin participants experienced a similar but more mild illness, which was not caused by leptospira. This conclusion was based on a higher attack rate for the Illinois participants (11% vs 5%), more frequent and severe illness that met the case definition (RR = 2.0), and an illness with an incubation period that was longer at 14 days. All hospitalized patients had participated in the Illinois event. On serologic testing by IgM ELISA, 43% of 70 Illinois participants who met the case definition were positive vs. none of the participants in Wisconsin. In order to further define the extent of the outbreak, Illinois residents who had recreational or occupational exposure to the lake water were tested; five were positive. The Illinois event occurred after heavy rainfall, which followed a period of dry weather. The potential animal source and leptospira serovar have not been determined, nor has the etiology of the Wisconsin illness been determined.

Comment by David R. Hill, MD, DTM&H

Both of these waterborne outbreaks, one causing diarrhea from infection with a protozoan, cryptosporidium, and the other causing a severe febrile illness from leptospira, document the potential hazards of fresh water swimming. These outbreaks were dramatic in many ways, but particularly in the number of persons involved. The cryptosporidium outbreak has been the largest outbreak of any infectious agent following exposure to recreational water, and the number of cases of leptospirosis nearly exceeds the total number of 50-150 cases reported each year in the United States.4 Both of these outbreaks occurred in the United States where water purity is generally assumed. However, when conditions are right, outbreaks of infectious agents can readily occur.5 Conditions contributing to these outbreaks probably occurred when rain water washed excessive amounts of contaminated material, human feces in the first case and infected animal urine in the second, into the lake water. Summer temperatures and prolonged exposure in the water also enhanced transmission.

In developing countries, infection with both of these agents is well-documented. Cryptosporidium, acquired through the fecal-oral route, is one of the most common agents infecting children in developing countries and accounts for about 6% of all cases of diarrhea in these regions.6 Although not a frequent cause of diarrhea in travelers, it is seen in a small percent of cases.7 Its relative resistance to chlorination and small size allow it to withstand efforts to purify public water supplies, as was seen in the massive outbreak of cryptosporidial diarrhea in Milwaukee in 1993.8 It has caused the CDC to examine ways to better control this parasite as well as other water-transmitted protozoans, such as Giardia lamblia.9 The contribution of cryptosporidium to diarrhea in HIV/AIDS patients is a major problem and causes significant morbidity in this population. It is fortunate that for most immunologically normal hosts, infection is self-limited over several days, since there is no reliably effective therapy.

The spirochetal agent of leptospirosis, Leptospira interrogans, is a widespread zoonosis endemic in both temperate and tropical climates.10 It is passed in the urine of infected animals, primarily rats, cattle, and dogs (wild animals may also be reservoirs) into the soil where it can persist in moist conditions. In periods of heavy rainfall, it can wash into water supplies. This association with flooding was demonstrated again in November 1998 in the aftermath of Hurricane Mitch. Guatemala, Honduras, and Nicaragua have experienced outbreaks of leptospirosis with more than 300 cases reported.

Humans acquire the agent as incidental hosts when it passes through mucous membranes, cuts, or abraded skin during either handling of infected animals or during recreational exposure to infected water.11 Illness usually begins abruptly with fever, chills, severe myalgias and headache; conjunctivitis, abdominal pain, diarrhea, rash, and meningeal symptoms can also be seen. Most cases are anicteric, but a small percent can progress to a life-threatening disease known as Weil’s syndrome with renal and hepatic involvement.10 The United States has relatively few cases each year, and most have originated from Hawaii.4,12 As indicated earlier, this agent has been well-documented in developing countries. Severe manifestations with pulmonary hemorrhage were documented in Nicaragua in 1995.13,14 Cases may also be confused with dengue fever as was recently reported from Puerto Rico.15 Bruce and colleagues recommend that if a dengue-like illness is associated with jaundice or dark urine and the patient has an appropriate exposure to leptospira, then leptospirosis should be considered.

Travelers have come into contact with this throughout the world, almost always during recreational exposure to fresh water (e.g., river rafting).16,17 Infection may be treated with penicillins or tetracycline,18,19 and doxycycline (200 mg weekly) can be used for prophylaxis when there is high-risk exposure.20

What do these outbreaks say for travel medicine specialists? They strengthen our admonition to travelers not to ingest untreated fresh water and to avoid swimming in rivers, lakes, and streams where human or animal contamination is known to exist, particularly following periods of heavy rainfall or flooding. Schistosomiasis, giardiasis, enteric bacteria, viruses, and the two reported agents, as well as others, may each be a potential risk in these situations. It also reinforces the importance of being able to recognize syndromes in returned travelers—to take their signs and symptoms and match them with an exposure history to develop a differential diagnosis. Two of the triathletes with leptospirosis went to surgery unnecessarily. Continued efforts to educate travelers on risk avoidance, along with heightening our own knowledge about potential travel-related illness, will help to maintain the health of our travelers.


1. Kramer MH, et al. First reported outbreak in the United States of cryptosporidiosis associated with a recreational lake. Clin Infect Dis 1998;26:27-33.

2. Centers for Disease Control and Prevention. Outbreak of acute febrile illness among athletes participating in triathlons—Wisconsin and Illinois, 1998. MMWR Morb Mort Wkly Rep 1998;47:585-588.

3. Centers for Disease Control and Prevention. Update: Leptospirosis and unexplained acute febrile illness among athletes participating in triathlons—Illinois and Wisconsin, 1998. MMWR Morb Mort Wkly Rep 1998; 47:673-676.

4. Centers for Disease Control and Prevention. Summary of notifiable diseases, United States, 1994. MMWR Morb Mort Wkly Rep 1994;43:1-80.

5. Kramer MH, et al. Surveillance for waterborne-disease outbreaks—United States, 1993-1994. In: CDC Surveillance Summaries, April 12, 1996. MMWR Morb Mort Wkly Rep 1996;45(No. SS-1):1-30.

6. Adel K, Sterling CR, Guerrant RL. Cryptosporidium and related species. In: Blaser MJ, et al, eds. Infections of the Gastrointestinal Tract. New York, NY: 1995: 1107-1128.

7. Jelinek T, et al. Prevalence of infection with Cryptosporidium parvum and Cyclospora cayetanensis among international travelers. Gut 1997;41:801-804.

8. MacKenzie WR, et al. A massive outbreak in Milwaukee of cryptosporidium infection transmitted through the public water supply. N Engl J Med 1994;331: 161-167.

9. Centers for Disease Control and Prevention. Assessing the public health threat associated with waterborne cryptosporidiosis: Report of a workshop. MMWR Morb Mort Wkly Rep 1995;44(No. RR-6):1-19.

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

11. Katz AR, et al. Leptospirosis on Oahu: An outbreak among military personnel associated with recreational swimming. Military Med 1997;162:101-104.

12. Katz AR, et al. Leptospirosis in Hawaii, 1971-1990: Clinical and epidemiologic analysis of 187 laboratory confirmed cases (abstract). Am J Trop Med Hyg 1995;53:241.

13. Centers for Disease Control and Prevention. Outbreak of acute febrile illness and pulmonary hemorrhage—Nicaragua, 1995. MMWR Morb Mort Wkly Rep 1995;44:841-843.

14. Hill DR. Leptospirosis in Nicaragua. Trav Med Advisor Update 1996;6:10-12.

15. Bruce MG, et al. Leptospirosis among patients with dengue-like illness in Puerto Rico (Abstract #72). Program and Abstracts of the 47th Annual Meeting of the American Society of Tropical Medicine and Hygiene. Am J Trop Med Hyg 1998;59(suppl 3):134-135.

16. van Crevel R, et al. Leptospirosis in travelers. Clin Infect Dis 1994;19:132-134.

17. Centers for Disease Control and Prevention. Outbreak of leptospirosis among white-water rafters—Costa Rica, 1996. MMWR Morb Mort Wkly Rep 1997;46:577-579.

18. McClain JBL, et al. Doxycycline therapy for leptospirosis. Ann Intern Med 1984;100:696-698.

19. Watt G, et al. Placebo-controlled trial of intravenous penicillin for severe and late leptospirosis. Lancet 1988;i:433-435.

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