title: Microbial groundwater quality and its health implications for a border-strip irrigated dairy farm catchment, South Island, New Zealand.
abstract: Intensification of dairying on irrigated pastures has led to concern over the microbial quality of shallow groundwater used for drinking purposes. The effects of intensive dairying and border-strip irrigation on the leaching of E. coli and Campylobacter to shallow groundwater were assessed over a three-year period in the Waikakahi catchment, Canterbury, New Zealand. Well selection excluded other sources of contamination so that the effect of dairying with border-strip irrigation could be assessed. Groundwater samples (135) were collected, mostly during the irrigation season, with E. coli being detected in 75% of samples. Campylobacter was identified in 16 samples (12%). A risk assessment of drinking water with these levels of Campylobacter was undertaken. A probability distribution was fitted to the observed Campylobacter data and the @RISK modeling software was used, assuming a dose response relationship for Campylobacter and consumption of 1 L/day of water. The probability of infection on any given day in the study area was estimated at 0.50% to 0.76%, giving an estimated probability of infection during the irrigation season of 60% to 75%. An epidemiological assessment of the Canterbury region comparing areas encompassing dairy within major irrigation schemes (approximately 55% border-strip irrigation) to two control groups was undertaken. Control group 1 (CG1) encompasses areas of dairying without major irrigation schemes, and a second larger control group (CG2) comprises the rest of the Canterbury region. Comparisons of the subject group to control groups indicated that there was a statistically significant increase in age-standardised rates of campylobacteriosis (CG1 Relative Risk (RR)=1.51 (95% CI = 1.31-1.75); CG2 RR = 1.51 (1.33-1.72)); cryptosporidiosis (CG1 RR = 2.08 (1.55-2.79); CG2 RR = 5.33 (4.12-6.90)); and salmonellosis (CG2 RR = 2.05 (1.55-2.71)).
authors.affiliation: Institute of Environmental Science and Research, PO Box 29 181, Christchurch, New Zealand. murray.close@esr.cri.nz
authors.forename: Murray
authors.initials: M
authors.lastname: Close
authors.forename: Rod
authors.initials: R
authors.lastname: Dann
authors.forename: Andrew
authors.initials: A
authors.lastname: Ball
authors.forename: Ruth
authors.initials: R
authors.lastname: Pirie
authors.forename: Marion
authors.initials: M
authors.lastname: Savill
authors.forename: Zella
authors.initials: Z
authors.lastname: Smith
mesh_terms: D002167:Campylobacter / Q000302:isolation & purification; D002169:Campylobacter Infections / Q000453:epidemiology*; D003612:Dairying; D004926:Escherichia coli / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology*; D005618:Fresh Water / Q000382:microbiology*; D006801:Humans; D009520:New Zealand / Q000453:epidemiology; D018570:Risk Assessment; D014871:Water Microbiology