Estimating the Frequency of Tap-Water Exposures To Mycobacterium avium Complex in the U.S. Population with Advanced AIDS

Abstract

Mycobacterium avium complex (MAC) is a group of ubiquitous and opportunistic bacterial pathogens included on the U.S. Environmental Protection Agency Drinking Water Contaminant Candidate List. The risk of contracting a disseminated MAC infection is primarily limited to the immunocompromised, including those with advanced acquired immunodeficiency syndrome (AIDS). These infections likely result from exposures to MAC-contaminated tap water, food, or soil, although the epidemiologic evidence is insufficient to implicate a specific medium. The objective of this study was to assess tap water exposure to MAC in the U.S. population with advanced AIDS, defined here as having fewer than 100 CD4⁺ cells/mm³ of blood. Using limited data on the detection of MAC and self-reported post-tap treatment practices, two exposure models were developed to simulate the likelihood of exposure to MAC via tap water consumption in this sensitive population. The first model integrated data from studies that described sources of water for consumption and post-tap treatment rates in cohorts infected with human immunodeficiency virus (HIV⁺). The second model used data from a study that categorized the fraction of water intake consisting of tap water that was not further treated. Approximately 1500 individuals with advanced AIDS were estimated to ingest tap water with detectable concentrations of MAC organisms daily. Additional studies on tap-water use in U.S. HIV⁺ populations are needed to confirm these findings. Longitudinal and cross-sectional studies on the occurrence of MAC in tap water, particularly in regions with large HIV⁺/AIDS populations, would help address some of the uncertainty in these exposure estimates.

Acknowledgments

The authors thank Drs. Scott Holmberg, Robert Horsburgh, Allyn Nakashima, Gerald Stelma, Mark Rodgers, Terry Covert, Robin Oshiro, Martha Embry, Greg Paoli, Michael Lederman, Glenn Suter, and Gunther Craun for their reviews, helpful comments, and additional information provided during the development of this assessment. We also thank the anonymous reviewers from the journal. The authors also thank Bette Zwayer, Lana Wood, Luella Kessler, Linda Ketcham, and particularly Ann Parker for their assistance during the development of this assessment.

Notes

Previous estimates of the fraction of the HIV-infected population with advanced AIDS (Sullivan et al., 1998) were much greater than the range of the distribution assigned to this fraction in this analysis. These data were collected when HIV infection commonly resulted in rapid immune system decline that lead to an acutely fatal condition. Widespread treatment of the HIV-infected population with antiretroviral therapies has led to immune-system reconstitution in much of this population. Current estimates of the size of the U.S. population with advanced AIDS are not available because of the lability of the number of CD4⁺ cells per cubic millimeter and patient confidentiality restrictions.

When specifically asked about possible additional exposures to tap water, all but one of the individuals in the study who reported no tap water consumption had at least one exposure to untreated municipal water (e.g., brushing teeth, water consumption at a restaurant).