Summer camp outbreak of cryptosporidiosis linked to ham and close proximity with infected person

CDC. MMWR. 2011; 60(27):918-922.

Issue: August 2011

An outbreak of cryptosporidiosis during a 2009 summer camp in North Carolina appears to have been a result of zoonotic transmission of Cryptosporidium parvum subtype, IIaA17G2R1, according to a new CDC report.

A total of 46 laboratory-confirmed and probable cryptosporidiosis cases were reported at the camp during July 2009. Campers included children as young as 5 years, but the campers were excluded from the analysis because of concerns about recall accuracy and because they had minimal variation in their camp activities, according to the report in a recent Morbidity and Mortality Weekly Report.

Analyses of data from a retrospective cohort study of staff members revealed that eating ham from a sandwich bar that included camp-grown raw produce and sharing a cabin with an ill person were significantly associated with illness.

Of 129 staff members, 123 (95%) completed the retrospective cohort study questionnaire. Results of the multivariable analysis indicated that only two factors were significantly associated with illness: ham from the sandwich bar on June 21 (adjusted prevalence ratio [aPR] = 3.5; 95% confidence interval [CI] = 1.6–7.4) and sharing a cabin with an ill person (aPR = 2.8; CI = 1.3–6.2).

Cryptosporidium isolates from stool specimens of livestock and humans at the camp were of the identical C. parvum subtype, which proved to investigators that zoonotic transmission had occurred, and suggested a link not implicated by traditional epidemiologic methods.

Traditional epidemiologic methods used in this outbreak investigation revealed a unimodal epidemic curve suggestive of a point-source exposure and that food was significantly associated with illness. However, the mechanism leading to food contamination could not be identified.

A bivariate analysis revealed that contact with calves or other livestock were not significantly associated with illness; however, molecular epidemiologic methods demonstrate that the C. parvum subtype IIaA17G2R1 transmitted at the camp likely came from livestock on the farm, which included cows, goats and pigs. The investigators wrote in their report that that C. parvum parasite may have been introduced into the camp by the calves brought to the location in May and June 2009.

Potential routes of transmission at the camp included several recreational water venues (a swimming pool, lake, and river), drinking water supplied by wells, meals served by a central kitchen, and a garden that provided more than one-half of the produce for camp meals. Part of the garden was located in an area adjacent to where the calves were kept.

Investigators said that along with hand washing, additional measures to protect against transmission of Cryptosporidium in camp settings are needed.

The incidence of reported cryptosporidiosis in the United States increased from one case per 100,000 population in 1999 to more than three cases in 2008.

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