Counting cytopathogenic virus adsorbed to cellulose nitrate membrane filters as a simple method for counting viruses in raw sewage and sewage effluents.

Using the VIRMETADEN (acronym derived from virus adsorption enumeration) method to count cytopathogenic viruses adsorbed to cellulose nitrate membrane filters from prefiltered and decontaminated sewage samples was shown to be feasible. The numbers of naturally occurring enteroviruses recovered by the VIRMETADEN method were significantly higher than those obtained by standard plaque assay. For prefiltration of sewage samples, low protein binding polyvinylidene fluoride (PVDF) membranes of 0.65 and 5 microm pore size proved to be at least as good as prefilters used previously, both in the volume that could be filtered and in the low virus retention. Regarding decontamination, 0.22 microm pore size PVDF membranes were as good as chloroform treatment. Alternatively, decontamination with 0.05% phenol followed by filtration through 0.65 microm PVDF membrane filters proved to be an excellent method for clarifying and decontaminating the sample prior to enumerating viruses using the VIRMETADEN method. It allows good recovery and greater decontaminated sample volumes. The application of VIRMETADEN to decontaminated raw sewage and secondary effluent gave recoveries of approximately 100% of vaccinal polioviruses seeded in sewage. The advantage of this approach is that the same method is applicable to sewage affluents and effluents with a simple and fast method, which implies lower material and labour costs.