Vibrios are more common in water temperatures over 17-20°C. They can survive in a range of adverse environmental conditions, in order to do this they enter a viable but non-culturable stage in which metabolic activities are minimal but they still retain pathogenicity. Several vibrio species are human pathogens and have been associated with wound infections (V. vulnificus) and ear infections (V. alginolyticus) after exposure to contaminated water, and gastroenteritis (V. parahaemolyticus and V. cholera) after consumption of contaminated food.
During the summer of 2006, four people developed V. alginolyticus infections after swimming in a large inlet on the North Sea, at separate but nearby locations. The water was then tested and both V. alginolyticus and V. parahaemolytis were found in the water samples. This study is follow up to previous finding of vibrio species in North Sea inlets. The quantification and typing of potentially human pathogenic vibrio species were looked at, as these areas had not been studied before. Vibrio numbers in bathing water were related to environmental conditions, for example water and salinity, and to European legislative requirements for bathing water quality.
In this study, Schet et al monitored four bathing sites in the Netherlands; samples at the bathing sites were taken biweekly or four-weekly from April to October. It was found that vibrio species were detected at all sites. There were 447 isolated vibrios from water samples found. 50.6% of these were V. alginolyticus and 8.5% were V. parahaemolyticus. The water temperatures ranged from approximately 10 to 21°C, no vibrio were detected in samples when the water was below 11°c. In the majority of the samples, faecal indicator levels were below the mandatory values for good water quality according to the European Bathing Water Directive. There was a correlation found between vibrio and E. coli concentration, however it was not a strong correlation. An even weaker correlation was found between intestinal enterococci and vibrio. Throughout the period of the study, only one case of a bathing water related vibrio infection was reported, swabs were taken and 2 V. clorae isolates were cultured from the wound.
Overall, potentially pathogenic vibrio species were detected, however lower numbers of vibrio were found than expected. This is due to colder bathing water temperatures than normal compared to other data looked at. This may be something to look at in the future and do the same experiments during another summer. The results underlie the need for further molecular studies on a larger number of clinical isolates and isolates from water samples to understand clonal distribution with seawater V. chloerae isolates in relation to bacterial pathogenicity, water salinity or environmental parameters. This study highlighted the need for education of public health workers, bathing water managers and the general public in order to prevent vibrio infections from bathing water exposure.
I chose to review this paper as I am interested in what actually is in bathing water; I was surprised to find these results especially as I have been swimming where some of the samples were taken from! I think that more studies need to address water quality in terms of vibrio content, especially as water temperatures could raise due to global warming and therefore have more favourable growth conditions for vibrio species.
F.M. Schets, H.H.J.L. van den Berg, A. Marchese, S. Garbom, A.M. de Roda Husman (2011). Potentially Human Pathogenic Vibrios in Marine and Fresh Bathing Waters Related to Environmental Conditions and Disease Outcome. International Journal of Hygiene and Environmental Health. Volume 214, Issue 5, September 2011, Pages 399–406.
Sophie - this is an interesting paper which links with the post on long term trends by Oliver on 8 October. There is some very convincing evidence of increased risk from vibrios in Notrth Sea and Baltic Sea in the paper by Baker-Austin et al. that I refer to in my comments to Oliver's post. I suggest you have look at that one!
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