Round robin investigation of methods for recovering human enteric viruses from sludge

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Abstract
To select a tentative standard method for detection of viruses in sludge the American Study for Testing and Materials D19:24:04:04 Subcommittee Task Group initiated round robin comparative testing of 2 procedures that, after initial screening of several methodologies, met the basic criteria considered essential by the task group. Eight task group member laboratories agreed to perform round robin testing of the 2 candidate methods, i.e., the Environmental Protection Agency or low pH-AlCl3 method and the Glass or sonication-extraction method. Five different types of sludge were tested. For each particular type of sludge, a single laboratory was designated to collect the sludge in a single sampling, make samples and ship it to the participating laboratories. In most cases, participating laboratories completed all the tests within 48 h of sample arrival. To establish the reproducibility of the methods, each laboratory tested each sludge sample in triplicate for the 2 candidate virus methods. Each processed sludge sample was quantitatively assayed for viruses by the procedures of each individual round robin laboratory. To attain a more uniform standard of comparison, a sample of each processed sample from all laboratories was reassayed with one cell line and passage number by a single laboratory. When the data were statistically analyzed, the Environmental Protection Agency method yielded slightly higher virus recoveries for all sludge types, except the dewatered sludge. The precisions of both methods were not significantly different. On the basis of these and several other considerations both methods are recommended as tentative American Society for Testing and Materials standard methods.