Exploring the Effect of Precipitation and Drought on Campylobacter and Salmonella Infections in the Southwest United States

Abstract

Weather variability affects enteric infections in people through the complex interaction of human, animal, and environmental factors. The studies presented in this dissertation examine the relationship between weather variability on Campylobacter and Salmonella infections in humans. In a review exploring pathogen-specific estimates for Campylobacter infections, research shows significant associations with myriad weather variables that might explain the changes in Campylobacter cases in different regions around the world (Aim 1). Specifically, research shows significant positive associations with temperature, precipitation, and relative humidity. Proximity to animal operations was not considered by the majority of papers, indicating a significant gap in our knowledge. Using the approaches described in the review, the associations with precipitation and drought were explored via an ecological analysis of Campylobacter (Aim 2) and Salmonella (Aim 3) infections in four Southwest US states from 2009-2021. Together the analyses show a significant and positive association between precipitation and Campylobacter and Salmonella incidence after adjusting for average temperature and drought. Variability in antecedent drought modifies this relationship, whereby infections increase following a heavy precipitation event during wet conditions (Campylobacter) or during early stages of drought (Salmonella) and are significantly decreased during extreme drought conditions for both pathogens. Proximity to animal operations modify this relationship between precipitation and incidence. Counties that have a high density of chicken and poultry, sheep and goats, or leafy green operations, have 2-3 fold increase in cases compared to counties without farm operations. Identifying the connection between weather variability and enteric infections provides insight into the complex mechanisms that drive increases in cases when no common risk factor is identified. The results of this dissertation will support public health departments in responding to and preparing for extreme weather events as they become more common with climate change.