New research has shown that climate change may be causing more than just an increase in extreme weather events such as heat waves and storms. Those events also seem to be bringing a heightened risk of Salmonella outbreaks with them.
The rates of people sickened by Salmonella rises each time their area experiences an extreme weather event, according to a new study published in Environment International and conducted by researchers at the University of Maryland.
To be precise, the researchers observed the risk of Salmonella infection increase 4.1 percent each time Maryland experienced an extreme heat or precipitation event. Those extreme weather events were defined as any time the state experienced temperatures or precipitation greater than the top 10 percent of hottest and wettest days from a 30-year baseline of 1960-1989.
Given that numerous climate studies anticipate extreme weather events increasing in frequency and intensity in the coming decades, health officials and communities will need to account for the additional foodborne illness burden resulting from these events, said Amir Sapkota, Ph.D., professor of epidemiology and biostatistics at the University of Maryland’s Institute for Applied Environmental Health and senior author of the study.
The increased risk of infection was also more pronounced in coastal areas compared to areas further inland. While extreme precipitation events resulted in a 3.6-percent increase of Salmonella infection risk to inland areas, they caused a 7.1-percent increase of risk in coastal regions.
The explanation for this is fairly simple: Extreme weather events give bacteria more of what they like.
“A lot of evidence shows that rising temperate and precipitation is conducive to bacterial growth and transmission,” Sapkota said. “Bacteria tend to multiply and grow better in warmer and wetter environments.”
But that’s just part of the story. Extreme weather events also cause flooding and water runoff that spreads and amplifies bacterial loads.
Take chicken farming as an example. Maryland produces more than 300 million broilers chickens each year on its Eastern Shore.
First, rising temperatures perpetuate the colonization and growth of Salmonella among flocks, likely leading to higher rates of contamination on poultry products.
Second, chicken manure is commonly used as fertilizer in Maryland. Once an extreme precipitation event rains down on a field fertilized with contaminated chicken manure, the manure runs off into streams, bodies of water, and even drinking wells, Sapkota said.
There have been numerous cases of children and others falling ill with bacterial infections after swimming or recreating in public bodies of water, and the runoff from food-producing fields is a likely explanation in many of those cases, he added.
One study cited by the team showed that Salmonella could persist in soil for as long as 405 days, providing ample opportunity for a precipitation event to spread it somewhere else.
Weather events likely affect coastal areas to a greater degree because not only do they have a higher concentration of people, but residents spend more time around water, where they increase their chances of exposure to harmful bacteria during water runoff events.
There could be exceptions to how well these observations translate for other foodborne pathogens such as E. coli and Listeria, but Sapkota said that the situation was most likely similar for any other bacteria.
Next, the team plans to continue studying the relationship between extreme weather and bacterial illness by expanding their study region to include states outside Maryland.
In the meantime, Sapkota said he hopes the study helps raise awareness about the connection.
“People should become aware of the issue to help themselves,” he said. “If you’re living in a coastal area and you have reason to believe the water may be contaminated during extreme precipitation events, then you should certainly reduce your family’s recreational activities.”
“Of course, the other big thing,” he added, “is to properly cook your food.”
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