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.)
