Open Access Research article

Endemic cryptosporidiosis and exposure to municipal tap water in persons with acquired immunodeficiency syndrome (AIDS): A case-control study

Tomás J Aragón13*, Suzanne Novotny3, Wayne Enanoria23, Duc J Vugia45, Asheena Khalakdina23 and Mitchell H Katz13

Author Affiliations

1 Department of Epidemiology and Biostatistics, and of Medicine, University of California, San Francisco, USA

2 Division of Public Health Biology and Epidemiology, School of Public Health, University of California, Berkeley, California, USA

3 San Francisco Department of Public Health, City and County of San Francisco, USA

4 California Emerging Infections Program, Oakland, California, USA

5 Division of Communicable Disease Control, California Department of Health Services, Berkeley, California, USA

For all author emails, please log on.

BMC Public Health 2003, 3:2  doi:10.1186/1471-2458-3-2

Published: 6 January 2003



In persons with acquired immunodeficiency syndrome (AIDS), Cryptosporidium parvum causes a prolonged, severe diarrheal illness to which there is no effective treatment, and the risk of developing cryptosporidiosis from drinking tap water in non-outbreak settings remains uncertain. To test the hypothesis that drinking tap water was associated with developing cryptosporidiosis, we conducted a matched case-control study among persons with AIDS in San Francisco.


Among patients reported to the San Francisco AIDS Registry from May 1996 through September 1998, we compared patients who developed cryptosporidiosis to those who did not. Cases were individually matched to controls based on age, sex, race/ethnicity, CD4+ T lymphocyte count, date of CD4+ count, and date of case diagnosis. Population attributable fractions (PAFs) were calculated.


The study consisted of 49 cases and 99 matched controls. In the multivariable analysis with adjustments for confounders, tap water consumption inside and outside the home at the highest exposure categories was associated with the occurrence of cryptosporidiosis (inside the home: odds ratio (OR), 6.76; 95% CI 1.37–33.5, and outside the home: OR 3.16; 95% CI 1.23–8.13). The PAF was 85%; that is, the proportion of cases of cryptosporidiosis in San Francisco AIDS patients attributable to tap water consumption could have been as high as 85%.


Although the results from this observational study cannot be considered definitive, until there is more data, we recommend persons with AIDS, especially those with compromised immune systems, consider avoiding tap water.