What do we test for?
Beachwatch monitors water at swimming locations to assess the level of faecal contamination. In urban areas the main source of faecal contamination is human sewage. Sewage poses a risk to human health because it can contain human pathogens. When sewage is detected, water may not be safe for swimming.
The new NHMRC 2008 guidelines advocate enterococci as the single preferred indicator organism for the detection of faecal contamination in recreational waters. Enterococci is found in the intestines of warm blooded animals and is present in very high numbers in raw sewage (millions of enterococci bacteria can be present in just 100 millilitres of raw sewage). Studies have found a strong relationship between elevated levels of this bacteria and illness rates in swimmers. It is important to note that enterococci does not cause illness, rather, it is measured to detect the presence of sewage and the possible presence of pathogens which do cause illness.
Prior to May 2009, Beachwatch also tested for the bacterial indicator faecal coliforms (also known as thermotolerant coliforms). While this bacterial indicator is also present in very high numbers in raw sewage, it dies off more rapidly than enterococci in marine waters and has been found to correlate poorly with illness rates in swimmers. The NHMRC 2008 guidelines do not advocate the use of faecal coliforms as a bacterial indicator for recreational waters.
Why don't we test for pathogens directly?
While pathogens are the organisms that cause illness, we don't test for these organisms directly for a number of reasons. Pathogens in sewage are generally present in lower numbers than the indicator bacteria. This means that large volumes of water need to be collected for analysis and the analytical procedures are generally more complex, more expensive and take longer. Also, as there are very many pathogens that could be present in sewage, it would be very difficult to choose which pathogen(s) to test for.
Indicator organisms are used to test for sewage contamination because they are easily detectable by simple laboratory tests, they are generally not present in uncontaminated waters and results are available relatively quickly.
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Page last updated: 15 February 2013