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
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