Estimation of virus density in sewage effluents by two counting techniques: comparison of precisions as a function of inoculum volume.

Two titration methods for the quantification of viruses present in the environment are compared--plaque counting and determination of the most probable number with a large number of inocula at each dilution. Titration of virus suspensions and of sewage samples showed that, for a given volume of inoculum, in most cases there was no statistically significant difference between the virus titres given by the two methods. The precision of the results was the same for the two methods. When the volume of inoculum used at each dilution differed from one method to another, the width of the confidence interval increased as the volume of inoculum decreased.