Cryptosporidial diarrhoea in South Australia. An exploratory case-control study of risk factors for transmission.

OBJECTIVE: To identify risk factors for transmission of cryptosporidiosis in South Australia.
DESIGN: Case-control study of 51 cases of laboratory confirmed cryptosporidiosis and 51 age and sex matched controls.
SETTING: Subjects from greater Adelaide, with cases notified by local pathology laboratories to the Communicable Disease Control Unit, South Australian Health Commission, during the summer of 1990/1991. PARTICIPANTS: One in 10 cases was selected systematically from 479 laboratory notifications, and permission was obtained from the treating physicians to contact the patients. Subjects nominated age and sex matched controls living in the same area.
METHODS: By means of a structured questionnaire, participants were asked by telephone about exposure to possible risk factors in the two weeks preceding the illness/interview. The risk factors included those most commonly cited in the literature as resulting in zoonotic, waterborne and person-to-person infection. The number and percentage of cases and controls exposed was recorded for each risk factor. The probability of having been exposed to selected risk factors was compared between cases and controls by the exact test for matched pairs.
RESULTS: The proportion of cases and controls exposed was similar for all risk factors except water sources. Controls were more likely to have consumed only rain water than were cases (P < 0.005). Cases tended more than controls to have consumed only spring water (P = 0.06) or only mains water (P = 0.09).
CONCLUSIONS: The consumption of spring water or mains water contaminated with cryptosporidial oocysts may be the mode of transmission of cryptosporidiosis in South Australia. The advent of specific methods for detecting Cryptosporidium sp. in water will allow this hypothesis to be tested.