Examining campylobacteriosis disease notification rates: Association with water supply characteristics

Campylobacter is the most frequent cause of bacterial enteric disease in New Zealand, often linked to food-borne transmission from contaminated fresh poultry. However, socioeconomic, agricultural, and environmental factors, including drinking water sources, also play a role in infections. About 15% of New Zealand residents rely on private water supplies, which are not regulated for water quality under the Water Services Act 2021. This situation poses a risk for waterborne transmission of Campylobacter. We analysed publicly notified cases of Campylobacter infection from 2015 to 2019 using Poisson regression models to evaluate the impact of water supply type, rurality, livestock density, and climate extremes on campylobacteriosis incidence. The results showed a significant association between private water supply in rural areas and increased campylobacteriosis incidence in high dairy density areas (Relative Risk (RR) = 2.21, 95% CI: 1.60-3.05). Higher dairy density was also linked to increased campylobacteriosis incidence, with low dairy density having an RR of 1.18 (95% CI: 1.04-1.34), medium density an RR of 1.17 (95% CI: 1.03-1.33), and high density an RR of 1.47 (95% CI: 1.28-1.69) in rural areas with private water supplies. These findings suggest that contaminated water may be a significant pathway for Campylobacter infection, indicating a potential need for additional support for private water users in rural areas.