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Journal of Water and Health Vol 06 No 4 pp 443–460 © IWA Publishing 2008 doi:10.2166/wh.2008.071
Large-scale freshwater microbiological study: rationale, results and risks
Desmond Till, Graham McBride, Andrew Ball, Ken Taylor and Eric Pyle
Public Health Microbiology Consultant, 5 Maire Street, Eastbourne, Wellington, New Zealand Tel.: +64 (0)4 562 7122 Fax: +64 (0)4 562 0134 E-mail: desmond.till@xtra.co.nz
National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Hamilton, New Zealand Tel.: +64 (0)7 856 1726 Fax: +64 (0)7 856 0151 E-mail: g.mcbride@niwa.co.nz
Institute of Environmental Science and Research (ESR), P.O. Box 29-181, Christchurch, New Zealand Tel.: +64 (0)3 351 6019 Fax: +64 (0)3 351 0010 E-mail: andrew.ball@esr.cri.nz
Environment Canterbury, P.O. Box 345, Christchurch, New Zealand
Ministry of Research, Science and Technology, P.O. Box 5336, Wellington, New Zealand
ABSTRACT
A fifteen-month fortnightly survey of microbial health risk indicators and pathogens has been carried out at 25 freshwater recreational and water supply sites distributed throughout New Zealand, for: E. coli, Clostridium perfringens spores, F-RNA bacteriophage, somatic coliphage, human enteroviruses, human adenoviruses, Cryptosporidium oocysts, Giardia cysts, Salmonella and Campylobacter. Sites were selected to represent five geographical areas covering New Zealand and five categories of predominant environmental impact: birds, dairy farming, forestry/undeveloped, municipal, and sheep/pastoral farming. Six of the sites were also source waters for treated drinking-water supplies. Of the indicators, E. coli was detected in 99 % of all samples, with somatic coliphage being detected most of the time (89 %). Of the pathogens tested, Campylobacter and human adenoviruses were inferred to be the most likely to cause human waterborne illness to recreational freshwater users. Using data from all sites, an estimated 5 % of notified campylobacteriosis cases in New Zealand could be attributable to water contact recreation. The critical value for E. coli as an indicator of increased Campylobacter infection is in the range of 200–500 E. coli per 100 ml. This result has been used to derive new national water quality guidelines for recreational fresh water in New Zealand.
Keywords: Campylobacter; catchment type; faecal indicators; microbiological seasonality; survey; risks; waterborne pathogens
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