Scientists analyze role of weather on Salmonella infections

Scientists have identified the most influential weather factors and combinations associated with an increase in Salmonella infections.

The study, led by a team of researchers at Surrey’s School of Veterinary Medicine, investigated the impact of different weather factors on the transmission of Salmonella. Their work was supported by animal health company Zoetis and the European Union’s Horizon 2020 research and innovation funding program. Findings were published in the Journal of Infection.

Key factors linked to a predicted increase in salmonellosis cases, regardless of geographical location, included air temperature above 10 degrees C (50 degrees F), relative humidity, reduced precipitation, dewpoint temperature of 7 to 10 degrees C (44.6 to 50 degrees F), and longer day lengths (12 to 15 hours). 

Salmonellosis incidence, weather and population data were pooled over time on the day infections occurred. The probable day of infection was estimated from the date the specimen was collected from the patient.

English and Dutch data
Surveillance data of confirmed salmonellosis cases reported to the UK Health Security Agency (UKHSA) in England and Wales during 2000 to 2016, and the National Institute for Public Health and the Environment in the Netherlands (RIVM) during 2015 to 2019 were used. The analysis included 144,703 Salmonellosis cases in England and Wales and 3,231 in the Netherlands.

There was a higher incidence in younger age groups, followed by over 90 year olds in England and Wales, while for the Netherlands, the highest incidence was in patients aged between 5 and 29.

Salmonella Enteritidis was the predominant serotype for both countries. In England and Wales, the three most common serovars were Salmonella Enteritidis, Salmonella Typhimurium (including the monophasic variant), and Salmonella Virchow.

Certain factors facilitate the ability for bacteria to multiply, while weather can have an indirect effect on consumer behavior, such as eating outdoors or improperly storing prepared food on sunny days.

“The model we used to analyze the data shows promise, as the findings were replicated across England, Wales and, independently, in the Netherlands, suggesting a potential for wider application in other European and high-income countries to help gain new insights on the incidence of Salmonella,” said Giovanni Lo Iacono, senior lecturer in Biostatistics/Epidemiology.

Model estimations
A statistical model was used to estimate the incidence of salmonellosis based on various combinations of three of 14 weather factors. The daily weather factors for England and Wales were extracted or calculated using Met Office data. Cases predicted by the model broadly captured the reporting patterns, including the summer peak, in the Netherlands.

Scientists said the impact of each factor on the risk of salmonellosis was not linear and depended on the interactions between them. In addition to weather, other factors could influence disease incidence, such as proximity to livestock farms, human behavior, and environmental variables.

Although food consumption tends to be indoors, the model used in the study reveals that outdoor weather conditions performed better than indoor ones. Scientists said it is to be expected that indoor settings are subject to greater environmental control, leading to more stable conditions compared to the outdoors. Seasonal incidence patterns are more likely to be related to outdoor events, such as barbecues, and the potential effect that weather has on them.

The methodology does not identify the causal pathway of salmonellosis. However, to test the hypothesis of infection driven by outdoor barbecues on a warm day, chicken sales data could be added to the model as a variable. 

“The study highlights how weather plays a significant role in Salmonella outbreaks and provides a valuable tool for predicting future risks and tailoring interventions, particularly in the context of climate change,” said Dr. Laura Gonzalez Villeta, first author of the study and researcher at the University of Surrey.

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Source: https://www.foodsafetynews.com/2025/02/scientists-analyze-role-of-weather-on-salmonella-infections/