The enterovirus test in the assessment of recreational water-associated gastroenteritis

This study reports the results of a series of analyses designed to identify possible mathematical relationships between the numbers of fecal streptococci vs the numbers of enteroviruses present (as measured by the enterovirus assay) in marine recreational waters in order to indirectly assess the relationship between enteroviral densities and subsequent risk of gastroenteritis among bathers exposed to marine waters contaminated with domestic sewage. A database consisting of 2066 parallel fecal streptococci and enterovirus enumerations taken from 416 different marine water locations throughout the United Kingdom was used in the analyses. Polychotomous logistic regression was used to model the probabilities of zero enterovirus, a possible infectious dose and a probable infectious dose of enterovirus being present over increasing fecal streptococci densities. The results of the polychotomous logistic regression analyses showed that the probability of the absence of enterovirus (i.e., zero enteroviruses being present) remained higher than the probability of the presence of either a possible or probable infectious dose in 101 of seawater up to a fecal streptococci density of 1000/100 ml of sample (actual estimated probabilities for the three groupings of enterovirus densities described above, at a fecal streptococci density of 1000 equaled 0.44, 0.44, and 0.12, respectively). In addition, the probability of zero enteroviruses being present remained higher than the probability of one or more enteroviruses being present in 101 of seawater up to a fecal streptococci density of 450/100 ml of sample. Since previously published epidemiological studies have shown an excess risk of gastroenteritis to occur among bathers exposed to as few as 32 fecal streptococci per 100 ml of sample, these results suggest that the actual viruses enumerated by the enterovirus assay are not etiologically related to recreational water-associated gastroenteritis. Since gastroenteritis has been the most consistently reported bathing water associated illness, these findings suggest the enterovirus assay to be of limited use in assessing marine recreational water quality given the increasing tendency to formulate water quality standards based on increased risk of gastroenteritis among bathers relative to non-bathers.