Case-control studies of Cryptosporidiosis (Melbourne and Adelaide)

Prof Christopher Fairley (Melbourne University)
Dr Martha Sinclair
Dr Brent Robertson
Assoc Prof Andrew Forbes
Martyn Kirk (OzFoodNet, ANZFA)
Mark Veitch (Melbourne University)

Funded by: Cooperative Research Centre for Water Quality and Treatment, The Water Services Association of Australia, Melbourne Water Corporation, South East Water Limited, Yarra Valley Water Limited, City West Water Limited

These studies assessed the importance of risk factors for cryptosporidiosis in Melbourne and Adelaide. These two cities have been chosen to represent the opposite ends of the water quality and treatment spectrum of Australian metropolitan water supplies: Melbourne - high quality source water with minimal treatment (chlorination only), Adelaide - lower quality source water with full conventional water treatment (coagulation, sedimentation, filtration and chlorination).

Eligible cases were people with confirmed cryptosporidiosis identified from pathology laboratory reports to the Dept. of Human Services VIC and Dept. of Human Services SA. These people were contacted by research nurses and asked to complete a telephone interview covering exposure to suspected risk factors in the two weeks before their illness developed. Controls were people without diarrhoeal illness selected at random from the White Pages telephone directory and matched by age and sex to the cases. The same questionnaire was adminstered to controls covering an equivalent time period as the respective matched case. Whenever possible, control interviews were completed within 3 working days of the matched case interview. To provide increased statistical power, 4 controls were matched to each case.

The risk factor exposures assessed included the following - type and quantity of water consumed, food and beverage exposure, travel, recreational water activities, gardening activities, contact with other people with gastroenteritis, contact with domestic and farm animals.

Data collection for the studies was completed in June 2001. In Melbourne, 239 cases and 956 controls were interviewed over 35 months. In Adelaide, 161 cases and 644 controls were interviewed over 31 months. Drinking water was not found to be a risk factor for cryptosporidiosis in either city. The major risk factors identified were swimming in public pools and person-to-person contact.

Robertson B, Sinclair M I, Forbes A B, Veitch M, Kirk M, Cunliffe D, Willis J and Fairley C K. Case-control studies of sporadic cryptosporidiosis in Melbourne and Adelaide, Australia. Epidemiol Infect 2002;128 (3):419-31.