Water Quality Indicators and the Risk of Illness at Beaches With Nonpoint Sources of Faecal Contamination

In the past many studies have found a relationship between the presence of faecal indicator bacteria and swimming-related illness in people exposed to water.  Although these studies are useful they were mostly conducted in areas where human sewage was the main source of pollution.  Currently used indicator bacteria may not be useful for non-point source contamination of water for example from animals because they may excrete bacterial indicators without human pathogens. There is a further problem relating to viruses as we have discussed in lectures. Even though there are some promising viral indicators they haven’t really been studies as predictors of health effects in bathers. The aim of this study was to look at the health effects experienced by bathers in relation to the water quality where nonpoint source contamination dominates.

The study was designed to look at whether the risk of illness increases with increased levels of traditionally used indicators and if contact with water increased the risk of illness for 2 weeks after contact. Participants were recruited on the same day as sampling, and their current health and degree of exposure to the water were recorded.  Three traditional indicators were used (enterococcus, total coliforms, fecal coliforms) which were measured by membrane filtration along with chromogenic substrates. Enterococcus was also measured using qPCR methods. Other indicators were measured  including Bacteroides, somatic coliphage, male-specific coliphage, adenovirus, and norovirus.

1892 samples were analysed, approximately 16% of these samples failed to meet water quality standards with 96% of these coming from enterococcus. Swimmers experienced more symptoms such as diarrhoea and a skin rash than non-swimmers and incidence of these symptoms increased with  different exposure categories i.e. those swallowing water showed highest percentage of symptoms. This increased risk was not seen for more severe symptoms such as vomiting or fever. The latter symptoms have been considered more relevant as it is difficult to tell if exposure to sea water and subsequent irritation could be responsible for symptoms such as a skin rash.

No correlation was observed between indicator levels and the risk of illness. In previous studies a link has been show but this is usually when human faecal contamination has been shown to be present. As the area is not known to have high level of human faecal contamination  the authors conclude that this lack of correlation may be attributed to this lack of human faecal indicators leading them to suggest that alternative bacterial indicators should be used where non-point source contamination is present.

I chose to review this paper as I thought it was interesting that the authors focused on non-point source contamination and compared it to the risk of illness. As with any study involving reports of illness from people it is dependent on how severe the people thought their symptoms were. Although the authors did a lot in an attempt to avoid problems with results for the human health outcomes but can never be totally be avoided.. I think that is interesting that the authors found no correlation between illness and levels of indicator bacteria. It is difficult to conclude that the symptoms seen were definitely due to exposure to sea water but  it highlights another problem with the use of certain indicators when non-point source contamination is a problem. This could be antoerh thing which should be taken into account with the EU bathing regulations.

Colford, J. Wade, T. Schiff, K. Wright, C. Griffith, J. Sandhu, S. Burns, S. Sobsey, M. Lovelace, G. Weisberg, S. 2007.  Water quality indicators and the risk of illness at beaches with nonpoint sources of fecal contamination.  Epidimiology 18; 27-35