Animal Waste, Water Quality and Human Health

424Animal Waste, Water Quality and Human Healthsuch as outbreak investigations and case-control studies, have provided logicallinkages to human infections with zoonotic pathogens and recreational oroccupational exposures to water, but they have not established a definitive linkbetween water contamination and specific animal sources.Three of the prospective studies were conducted in marine or estuarine watersand one was conducted at a freshwater beach. Two of these studies werespecifically designed to answer the question “Do bathing waters contaminated bynon-human faeces pose a risk to swimmers?” In both studies efforts were madeto ensure that animals and birds were the dominant source of the faecalcontamination. This was done in one case by surveying the watershed anddetermining human wastes were not being discharged into streams that fed intothe bathing water area (Calderon 1991). In the second case (Colford 2007) anextensive pre-study was performed using microbial source identification methodsto determine if human faeces were contaminating the beaches. In the third case(Cheun 1990) the dominant source of non-human faecal contamination wasidentified as being related to wastes that were discharged to a river thatcontaminated the water at two of the beaches that were studied. In the fourth case(McBride1998) the beaches studied were characterized as receiving dischargesfrom oxidation ponds, rural runoff or not receiving known sources of faecalcontamination. The sources of faecal contamination were not specifically identified.The levels of faecal contamination at the study locations, as measured by faecalindicator bacteria, were not unusual. Enterococci and E. coli were measured at threeof the study locations while only enterococci was measured at the San Diegolocation. The enterococci geometric mean densities per 100 ml at all fourlocations ranged from 17 to 144. The geometric mean E. coli densities per 100ml at the Hong Kong, Connecticut and New Zealand locations ranged from 25 to1,705. In similar epidemiological studies conducted at beaches contaminated byhuman sources (sewage effluents) with indicator densities at these same levels,swimming-associated gastroenteritis has been frequently observed. In the studywhere the beaches were characterized as receiving rural run-off, the densities offaecal indicator bacteria were very low, averaging eight per 100 ml at 1 beachand 30 per 100 milliliters at a second beach. This unusually low level of faecalcontamination is likely to have hindered the ability to draw clear-cut conclusionsabout whether rural run-off is related to swimming-associated gastroenteritis.All of the studies used a health endpoint similar to or identical to the HighlyCredible Gastrointestinal (HCGI) symptomatology first described by Cabelli(1983), in which combinations of the symptoms (vomiting, diarrhoea, nauseaand fever) were used to confirm a case of gastroenteritis.After observing the results of these studies the question can be asked, can the lackof excess faecal-associated illness in swimmers be taken as evidence that animal