Cryptosporidiosis-associated mortality following a massive waterborne outbreak in Milwaukee, Wisconsin

Objectives. This study estimated the magnitude of cryptosporidiosis-associated mortality in the Milwaukee vicinity for 2 years following a massive waterborne outbreak. Methods. Death certificates were reviewed. Results. During approximately 2 years before the outbreak, cryptosporidiosis was listed as an underlying or contributing cause of death on the death certificates of four Milwaukee-vicinity residents. In the approximately 2 years after the outbreak, this number was 54, of whom 85% has acquired immunodeficiency syndrome (AIDS) listed as the underlying cause of death. In the first 6 months after the outbreak, the number of death certificates indicating AIDS, but not cryptosporidiosis, as a cause of death was 19 (95% confidence interval = 12,26) higher than preoutbreak trends would have predicted. Conclusions. Waterborne outbreaks of cryptosporidium infection can result in significant mortality, particularly among immunocompromised populations. Any discussion of policies to ensure safe drinking water must consider the potential fatal consequences of waterborne cryptosporidiosis among immunocompromised populations.