Study finds Southeast's rural landscapes pose potential risk for salmonella infection

Researchers from the University of Georgia have determined that various freshwater sources in Georgia, such as rivers and lakes, could feature levels of salmonella that pose a risk to humans. The study is featured in the July edition of PLOS One.

Faculty and students from four colleges and five departments at UGA partnered with colleagues from the Centers for Disease Control and Prevention and the Georgia Department of Public Health to establish whether or not strains of salmonella exhibit geographic trends that might help to explain differences in rates of human infection.

"In this study, salmonella isolated from water and wildlife were collected over a period of 10 years from distinct rural areas in Georgia, both geographically—north versus south—and in terms of prevalence of salmonellosis in humans—lower versus higher. Because Georgia has some of the highest case rates for reported salmonella infections in the nation, this was an ideal area to begin to examine the ecology of salmonella," said study co-author Erin Lipp, a professor of environmental health sciences in the UGA College of Public Health.

Salmonella infections are one of the top causes of gastrointestinal disease in the U.S., and while regulatory agencies have made progress in reducing foodborne transmission of the pathogen, other infection sources, including exposure to water, have not been as thoroughly examined.

To complete this research, the scholars collected samples from two different geographic regions of Georgia—the low-lying coastal plain and the piedmont, which is higher in elevation. Data was collected from six stations in the Little River watershed near Tifton, which has one of the highest case rates for salmonellosis in the state, and along the North Oconee River in Jackson County, a lower case rate area in Georgia. Water samples from all sites were gathered from December 2010 to November 2011. Samples from surrounding wildlife were also collected, and archived samples from these areas dating back to 2005 were also included.

Most significantly, the research team found that water sources could be an underestimated source of salmonella exposure to humans. Though the frequency that salmonella was found in north and south Georgia was similar, salmonella strains with DNA fingerprints matching those found in humans were more commonly found in south Georgia.

Specifically, rural areas of south Georgia had matches between the environment and humans at the 90 percent rate for salmonella Muenchen, a strain commonly associated with human cases. The researchers also found that wildlife, especially small mammals like raccoons and opossums frequenting these freshwater sources, could be carriers of the salmonella pathogen.

"Salmonella is a highly diverse and apparently well-adapted bacterium in the Southeastern U.S., and environmental exposures may be important in understanding and eventually mitigating risk from this agent," Lipp said.

By studying how salmonella interacts with its environment, the UGA team hopes to gain a better understanding of how it can be controlled. They are interested in continuing their work on this issue by further examining the linkage between animals, humans and their shared environments to determine how the bacteria moves through various host organisms. The researchers also hope to explore the impact of different variables in salmonella's physical environment, such as the role of climate and weather.

"This study brought together scientists with diverse expertise in ecology, geography, environmental sciences, microbiology, molecular biology and epidemiology to tackle a complex and daunting question," said John Maurer, the paper's principal author and professor of population health in UGA's College of Veterinary Medicine.