Waterborne outbreaks of cryptosporidiosis

A review of 35 outbreaks of cryptosporidiosis points to recommendations for prevention of waterborne outbreaks and uncovers a need for more adequate epidemiological data. Cryptosporidium parvum infection occurs worldwide in urban and rural populations, and waterborne outbreaks have been associated with consumption of contaminated drinking water and water during recreational activities. This article reviews the epidemiology and causes of waterborne outbreaks that have been reported in North America and the United Kingdom. Outbreaks were associated with filtered and unfiltered surface water sources, groundwater sources, and contamination of the distribution system. In most outbreaks, sources of contamination and deficiencies in treatment and operation were identified. Available epidemiological information is inadequate to estimate endemic waterborne risks, and analytical studies should be conducted to assess these risks. A major issue to consider in assessing waterborne cryptosporidiosis risks is the role of protective immunity, which may be acquired through low‐level sporadic exposures to C. parvum in drinking water.