Heavy rainfall, dairy cattle and <em>Campylobacter</em> in Aotearoa New Zealand: space-time stratified case-crossover study — The Association Specialists
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  3. Heavy rainfall, dairy cattle and Campylobacter in Aotearoa New Zealand: space-time stratified case-crossover study

Heavy rainfall, dairy cattle and Campylobacter in Aotearoa New Zealand: space-time stratified case-crossover study (23586)

Simon Hales 1 , Alice Kim 1 , Michael Baker 1 , Farnaz Pourzand 1 , Tim Chambers 2
  1. University of Otago, Wellington, WELLINGTON, New Zealand
  2. Ngai Tahu Research Centre, University of Canterbury, Chrishchurch, Canterbury, New Zealand

Objective
Here we investigate short-term associations between rainfall, dairy cattle density,
drinking water characteristics and notifications of sporadic campylobacteriosis.

Methods
Daily notifications of campylobacter were spatially linked to public drinking water
supplies. We created 10km circular buffer zones around abstraction points for each
supply and calculated dairy cattle density, average rainfall and maximum temperature
over 7-day lag periods. We fitted conditional Poisson regression models in a space-
time stratified case-crossover study.

Results
In the lowest quintile of dairy cattle density (zero cows/km2), there was an increased
risk of campylobacter in the 10th (highest) decile of 7-day average lagged rainfall: IRR
1.11 (95%CI: 1.02-1.22). In the highest quintile of dairy cattle density (~150 cows/km2)
there was an increased risk of campylobacter in the 6th to 10th deciles of rainfall, with
a dose-response relationship.

Conclusions
The risk of sporadic campylobacteriosis was significantly associated with heavy rainfall
in the 7 days prior to disease onset, especially in locations served by surface water
supplies with a high density of dairy cows.

Implications for public health
Heavy rainfall may increase the risk of sporadic disease, especially where there is a
high environmental load of zoonotic pathogens.

  1. Farnaz Pourzand, Alice H.M. Kim, Tim Chambers, Leah Grout, Michael G. Baker, Simon Hales, (2025) Examining campylobacteriosis disease notification rates: Association with water supply characteristics. Environmental Research. Volume 271. https://www.sciencedirect.com/science/article/pii/S0013935125003159?via%3Dihub
  2. M. Puente-Sierra, T. Chambers, L. Marek, J.M. Broadbent, B. O'Brien, M. Hobbs, (2023). The development and validation of a nationwide dataset of water distribution zones in Aotearoa New Zealand: A cross-sectional geospatial study. Data in Brief. Volume 49. https://www.sciencedirect.com/science/article/pii/S2352340923004687?via%3Dihub
  3. Tim Chambers, Simon Hales, Farnaz Pourzand, Frank Dean, Alice Hyun Min Kim, Mario Puente-Sierra, Lukas Marek, Matt Hobbs & Michael G. Baker (2026). Drinking water quality and enteric disease: a nationwide case-crossover study (2015–2019) in New Zealand. J Expo Sci Environ Epidemiol https://doi.org/10.1038/s41370-026-00857-8