LT2 cryptosporidium data: what do they tell us about cryptosporidium in surface water in the United States?

Beginning in 2006 a United States Federal regulation required public water suppliers using surface water serving more than 10,000 population to analyze for Cryptosporidium in at least 24 consecutive monthly samples from each surface water source. In July 2012, the U.S. EPA released the resulting data consisting of ca. 45,000 records. No Cryptosporidium were found in 93% of samples and no Cryptosporidium were found in any samples analyzed from over half of 1670 locations sampled. Nevertheless, at 250 locations representing every region of the U.S., Cryptosporidium were found in sufficient numbers of samples to provide a picture of their occurrence nationwide. Data from about 100 sites reporting the highest numbers were examined in detail. Although analysis of matrix spikes was required for quality control, the results do not permit estimating organism concentrations. The data reported at each of the individual sample locations were analyzed in the form of cumulative probability distributions to describe ke...