Spatial Effects of Livestock Farming on Human Infections with Shiga
Toxin-Producing Escherichia coli O157 in Small But Densely Populated
Regions: The Case of the Netherlands
Abstract
The role of environmental transmission of typically foodborne pathogens
like Shiga toxin-producing (STEC) O157 is increasingly recognized. To
gain more insights, we assessed the spatial association between sporadic
STEC O157 human infections and the exposure to livestock (i.e. small
ruminants, cattle, poultry, and pigs) in a densely populated country:
the Netherlands. This was done for the years 2007-2016, using a
state-of-the-art spatial analysis method in which hexagonal areas with
different sizes (90, 50, 25 and 10 km2) were used in combination with a
novel probability of exposure metric: the population-weighted number of
animals per hexagon. To identify risk factors for STEC O157 infections
and their population attributable fraction (PAF), a spatial regression
model was fitted using integrated nested Laplace approximation (INLA).
Living in hexagonal areas of 25, 50 and 90 km2 with twice as much
population-weighted small ruminants was associated with an increase of
the incidence rate of human STEC O157 infections in summer (RR of 1.09
[95%CI;1.01-1.17], RR of 1.17 [95%CI;1.07-1.28] and RR of 1.13
[95%CI;1.01-1.26]), with a PAF of 49% (95%CI;8-72%). Results
indicate a potential transmission of STEC O157 from small ruminants to
humans via the environment. However, the underlying mechanisms warrant
further investigation and could offer new targets for control.
Furthermore, the newly proposed exposure metric has potential to improve
existing spatial modelling studies on infectious diseases related to
livestock exposure, especially in densely populated countries like the
Netherlands.