Question - What factors account for the summer seasonal peak of Cryptosporidium related infections?
Answer - The cited reference notes ”The number of treated recreational water–associated outbreaks caused by Cryptosporidium drives the summer seasonal peak in both waterborne cryptosporidiosis outbreaks and cryptosporidiosis outbreaks overall. A treated recreational water–associated cryptosporidiosis outbreak can result in hundreds or thousands of cases, because 1) an infected swimmer can excrete 107–108 oocysts in one diarrheal incident in the water (3); 2) Cryptosporidium oocysts can survive >7 days at CDC-recommended concentrations of >1 ppm free available chlorine (4); and 3) swimmers might use multiple recreational water venues.” (Gharpure R et al. Cryptosporidiosis outbreaks- United States, 2009-2017. MMWR Morb Wkly Rep 2019; 68:568-572)