CP-2002-07
ale-specific RNA coliphages are reliable markers of sewage (point source) contamination
Luther, K. and R. Fujioka
Concentrations of U.S. Environmental Protection Agency-approved fecal indicator bacteria (fecal coliform, E. coli, enterococci) in environmental waters are used to determine the extent of sewage contamination and to establish recreational water quality standards. These water quality standards are used to determine the risk or probability that someone using that body of water for primary contact recreational use (e.g., swimming) will become ill from sewage-borne pathogens. The current EPA-recommended marine recreational water quality standards were developed from results of previously completed epidemiological and water quality studies at three beach sites (New York City, Boston Harbor, and Lake Pontchartrain) in the United States. These sites were selected because concentrations of fecal bacteria were barely acceptable due to nearby sewage discharges. Similar studies were conducted for fresh recreational waters at lakes in Pennsylvania and Oklahoma. Results of these studies (Cabelli et al., 1982; USEPA, 1986) have led to different recreational water quality standards for marine waters and for fresh waters. For marine waters, the EPA-recommended recreational water quality standard is a geometric mean concentration of 35 enterococci/100 ml based on five weekly samples taken over a month. For fresh waters, the EPA-recommended standards are similar geometric mean concentrations of 33 enterococci/100 ml or 126 E. coli/100 ml. The results of these EPA studies showed that concentrations of enterococci in marine and fresh waters correlated with incidences of swimming-associated gastroenteritis whereas concentrations of E. coli correlated with swimming-associated gastroenteritis only in fresh waters. A significant conclusion of the EPA studies was the finding that concentrations of fecal coliforms in marine and fresh waters did not correlate with swimming-associated gastroenteritis. EPA concluded that the most likely sewage-borne pathogens causing gastroenteritis was Norwalk type viruses (Cabelli et al., 1982). It was concluded that E. coli was too unstable in marine waters to serve as a reliable surrogate for the presence of sewage-borne pathogens. It should be noted that EPA conducted a similar epidemiological study at a lake in Connecticut. This lake was not contaminated with sewage, and fecal indicator bacteria in the lake were from non-point sources such as wild animals rather than from a point source (sewage). Under these conditions, the concentrations of enterococci and E. coli did not correlate with swimming-associated gastroenteritis (Calderon et al., 1991).