Faecal streptococci as faecal pollution indicators: A review. Part II: Sanitary significance, survival, and use

Abstract

Some New Zealand regional councils are examining the use of faecal streptococci (or the subset, enterococci) to assist in identifying pollution sources, or as better indicators of disease risk in bathing waters than faecal coliforms. However, in spite of worldwide investigation, faecal streptococci have largely failed to fulfil their potential as pollution source (human versus animal) indicators in receiving waters. Many qualifications accompany the use of faecal coliform: faecal streptococci (FC: FS) ratios, and the species identification approach (using biochemical and DNA‐based methods) has produced inconclusive results. Nevertheless, the FC: FS shift method (in which the ratio changes under sample storage) may warrant further investigation. Although reported results vary widely, most studies indicate that faecal streptococci outlive faecal coliforms in receiving waters and are more resistant to sunlight‐induced inactivation. USEPA epidemiological studies showed that enterococcus concentrations were better correlated than faecal conform concentrations with disease risk associated with bathing in sewage‐polluted waters. These results, which implied that the enterococci better represented viral hazard, led the USEPA to recommend the use of enterococci (or Escherichia coli in freshwaters) as bathing water quality indicators. These recommendations have largely been followed in provisional New Zealand Department of Health guidelines. However, adoption of the USEPA criteria should be approached cautiously, because of doubts about their epidemiological applicability in New Zealand, and a lack of information about streptococcal concentrations and species profiles in local effluents and receiving waters.