Pasture, Poos and People: a Space-Time Analysis of Livestock Density and Cryptosporidium Infections in Humans

Abstract

Enteric zoonotic infections in New Zealand are among the highest in the developed world. The country has recently experienced rapid intensification of livestock production, in response to the global demand for dairy products. However, the environmental health risks associated with agricultural intensification are poorly understood. We used spatio-temporal methods to analyse weekly notifications of human Cryptosporidium infections (1997-2008, N=8688) geocoded to census area units (N= 1769). Explanatory variables included livestock density (sheep, beef and dairy cattle, poultry, pigs), temperature, rainfall, drinking water quality and demographic data, interpolated where necessary to match the notification data. Infection hotspots recurred consistently in a region of intensified dairy cattle production (p<0.05). Multivariate analysis identified living in a rural area (IR 1.64 (95%CI 1.48-1.83)), dairy cattle density (IR 1.058 (95% CI 1.02-1.09)), and the proportion of children under 4 years old (IR 1.16 (95% CI 1.10- 1.23)) as significant risk factors for infection. Population density (IR 0.88 (95% CI 0.82-0.93)), the proportion of the population = 65 years (IR 0.88 (95% CI 0.83- 0.93)), the proportion identifying with Maori (IR 0.21 (95% CI 0.11- 0.38), Pacific Island (IR 0.10 (95% CI 0.04- 0.25) and Asian ethnicities (IR 0.11 (95% CI 0.05-0.27) and weekly average temperature (IR 0.91 (95% CI 0.86- 0.97) were inversely associated with risk of infection. Further expansion of the dairy farming sector is likely. In New Zealand, such livestock intensification may lead to increases in zoonotic infections, especially in rural preschool children. These findings suggest opportunities for targeted interventions to reduce the health impacts of intensified livestock production.