Estimating the infection risk in recreational waters from the faecal indicator concentration and from the ratio between pathogens and indicators

In the past, a series of epidemiological studies have been conducted with the aim of establishing a relationship between the concentration of faecal indicators and the number of bathing related illnesses. The final goal was to find a level of faecal indicators which could be considered acceptable under the point of view of the risk of infection. Because epidemiological studies are costly, additional means of obtaining health-related standards are desirable, which are easier to carry out and more affordable than epidemiological studies. In this paper, we have made an attempt to develop such an alternative. Setting out from published data on the dose response relationship for rotaviruses in humans, and from the lognormal distribution of faecal indicators assumed to exist in surface waters, we have established a series of equations which link the concentration of faecal indicators with the risk of infection.