Building a better protozoa data set

Abstract

Comparisons of ICR and ICRSS data indicate the Supplemental Surveys' improved methodology and procedures yield more accurate data on protozoa occurrence.The Information Collection Rule Supplemental Surveys (ICRSS) were designed to supplement the ICR with more reliable information on protozoa occurrence. The surveys benefitted from measures that were not part of the ICR, notably an improved protozoa detection method, an expanded quality control (QC) program, and a centralized sample control center. Based on analyses of data from the protozoa monitoring portion, the ICRSS have yielded measurable improvements in the quality of protozoa occurrence data available to support current rulemaking efforts. Compared with ICR results, ICRSS field sample data are characterized by higher detection rates and fewer potential false‐positive results. Data from more than 400 source water QC samples analyzed during the surveys indicated mean Cryptosporidium recoveries of 43 percent and mean Giardia recoveries of 53 percent from field samples spiked with laboratory strains of these organisms. Results confirmed that the performance of methods 1622 and 1623 during monitoring of 87 US source waters was consistent with their anticipated performance, demonstrated through interlaboratory validation studies conducted before surveys began.