Effect of environmental factors on microbial indicators and pathogenic agents

Hygienic-microbiological inspections of lakes and rivers used for bathing activities are carried out using microbial indicators (indicator bacteria and viruses), which enter the waters as pathogenic agents mainly via the discharge of municipal wastewater. Indicators such as Escherichia coli (E. coli) and intestinal enterococci are normally harmless, since they are non-pathogenic inhabitants of the human intestines. Indicators as well as pathogenic agents are normally not able of reproducing in surface water, but they can survive for a while depending on the prevailing conditions (water temperature, wastewater load etc.).

When defined concentrations of these indicators are exceeded, it is assumed that pathogenic agents are also present in concentrations, which can endanger the health of bathers. In September 2002, a study on the survival of both indicators and pathogenic agents was carried out by the Umweltbundesamt in order to check the reliability of the indicators. Preliminary results indicate that certain viruses (coliphages) are more resistant towards environmental effects than the two bacterial indicators E. coli and intestinal enterococci. This tentative conclusion still has to be verified in further studies in particular for the summer (bathing) season.