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Scientists study link between weather, Salmonella

By Cat Holmes
University of Georgia

If Salmonella were a good thing, Georgia would have bragging rights. The number of cases reported in the state is much higher than the national average.

Areas in south Georgia have an unusually high number of cases. And often public health officials haven't found a foodborne source.

"If it's not coming from food, then chances are the source is water," said Erin Lipp, a University of Georgia environmental microbiologist.

Lipp is the lead scientist in a group studying whether waterborne bacteria levels, specifically Salmonella and Campylobacter, rise in Georgia watersheds during periods of heavy rain.

We're No. 1

Salmonella is one of the top three causes of diarrhea in the United States. Georgia ranks No. 1 in reported cases among the 10 states taking part in FoodNet, a surveillance system by which the Centers for Disease Control and Prevention monitor major sources of U.S. foodborne illnesses.

Diarrhea may seem a small concern to people with effective medicines. But worldwide, it kills an estimated 3 million people, mostly children, each year. Waterborne bacterial infections may account for half of the deaths, according to the CDC.

Contaminated water is an obvious problem in developing countries with little or no water treatment. But researchers suspect many U.S. diarrhea cases may be waterborne, too, despite modern water treatment systems.

Weather connection

And outbreaks due to waterborne pathogens may be connected to the weather.

If a correlation could be mapped out between rainfall and bacteria outbreaks, scientists could predict outbreaks.

"Both human sewage and agricultural runoff contribute to the waterborne incidence of diseases like Salmonella and Campylobacter," Lipp said.

To study the problem, Lipp got a $600,000 grant from a partnership among the National Oceanic Atmospheric Administration, Environmental Protection Agency, National Science Foundation and Electric Power Research Institute.

Dana Cole, a UGA epidemiologist in large-animal medicine, and researchers at the University of Arizona and the Georgia Division of Public Health will work with Lipp.

Rates rise

Salmonella rates in humans rise in late summer, Lipp said, when rains usually increase.

The scientists will use data collected since 1948 to retrace El Niño events along with precipitation and streamflow in Georgia to create a historical weather model.

El Niño is a disruption of the ocean-atmosphere system in the tropical Pacific that affects weather worldwide. It increases rainfall across the southern United States. The historical weather model will be used to pinpoint local areas that may be strongly affected by El Niño, Lipp said.

"Among the predicted global climate-change scenarios is an increase in storm activity," Lipp said. "Therefore, we can use El Niño as a proxy for climate change.

Significant changes

"We'll be looking for significant changes in Georgia weather associated with El Niño, including significant increases in rainfall," she said. "Then we'll look for human outbreaks of Salmonella and Campylobacter associated with those increases."

The final step will be to "match bacteria collected from the environment with those taken from patients, using genetic fingerprinting," Lipp said.

Lipp first became interested in the connection between weather patterns and human pathogens while she was doing research in the pristine waters of Charlotte Harbor in southwest Florida.

Surprising discovery

It was 1998, El Niño was in effect and December rainfall was unusually high. While examining microbes in open shellfish beds, she discovered surprising data: Infectious human viruses were in 75 percent of the water stations they were monitoring.

Detection of these viruses was highly correlated with the amount of rain that fell during the week before the samples were collected. And the high rainfall amounts were due to El Niño, Lipp said.

"We suspected that water treatment plants and septic systems were failing due to the increase in rainfall," she said.

Because Salmonella and Campylobacter rates go up in certain seasons, she added, researchers have suspected a link between climate and bacteria for some time.

(Cat Holmes is a science writer with the University of Georgia College of Agricultural and Environmental Sciences.)

(Cat Holmes was a science writer with the University of Georgia College of Agricultural and Environmental Sciences.)

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