Temperature Influences on Salmonella Infections across the Continental United States

Salmonella spp. are one of the most common causes of gastrointestinal illness in humans. Elevated temperatures increase Salmonella spp.'s growth rate and likelihood that the food consumer will develop a severe illness. Climate and Salmonella associations have only been reported for a few U.S. states. This study investigated associations between temperature and reported human Salmonella infections from 2006 to 2014. The study analyzed state-level relationships across the contiguous United States. States voluntarily report weekly human Salmonella cases to the Nationally Notifiable Diseases Surveillance System. Representative weather conditions were created by population weighting temperature from the North American Land Data Assimilation System. Time series analysis using generalized additive models associated temperature against Salmonella infections while controlling for temporal patterns and the size of the population at risk. The study also investigated temperature and Salmonella infection transmission thresholds. In twenty-five states, higher weekly temperatures increased reported Salmonella infections. Each degree (°C) rise in temperature increased the risk of reporting a case by 1.3 to 5.9 percent. Many of these states were located in the Southwest, east central states, Midwest and Great Plains, and Northeast regions. Only temperatures above a state-specific threshold increased cases in four states. Above each threshold, a 1°C temperature increase translated into 5.6 to 22.8 percent more cases. Weekly temperatures increased reported human Salmonella infections across a much larger portion of the United States than published research suggests. Knowledge of places and periods of time where climate increases Salmonella risk can help target surveillance and health interventions.