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
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.