If you thought untreated surface water contaminated with salmonella is a rarity, a new study is suggesting a rething.
The research team, from University of Georgia, tested water over a one-year period in rivers and streams in a region of south Georgia known for its high rate of sporadic salmonella cases.
The team found Salmonella in 79 percent of water samples, with the highest concentrations and the greatest diversity of strains in the summer and after rainfall.
"Streams are not routinely tested for Salmonella, and our finding is an indication that many more could be contaminated than people realize," said Erin Lipp, associate professor in the UGA College of Public Health.
"We found our highest numbers in the summer months, and this is also the time when most people get sick," he added.
Lipp, who co-authored the study with former UGA graduate student Bradd Haley and Dana Cole in the Georgia Division of Public Health, said that although contaminated water used to irrigate or wash produce has been linked to several well-publicized outbreaks of salmonellosis in recent years, the environmental factors that influence Salmonella levels in natural waters are not well understood.
She said that understanding how Salmonella levels change in response to variables such as temperature and rainfall are critical to predicting-and ultimately preventing-the waterborne transmission of the bacteria.
The team studied streams in the upper reaches of the Suwannee River Basin, which begins in south Georgia and flows into central Florida.
The study area contains a mix of forested lands, row crops, pasturelands, wetlands and small cities.
The diversity of Salmonella strains was highest near a farm containing cattle and a pivot irrigation system, suggesting that close proximity to livestock and agriculture increase the risk of contamination.
The researchers also found a strong and direct correlation between rainfall for the two days preceding sample collection and the concentration of Salmonella, suggesting that runoff contributes to the contamination.
Overall, the study found that the diversity and concentration of Salmonella increased as temperatures increased.
The highest concentrations and greatest diversity of strains were found in August, the warmest month of the year.
According to Lipp, the study lends support to the idea that Salmonella illnesses could increase as a result of global warming.
"We also have the potential to decrease the likelihood of larger outbreaks related to produce, because in many cases contaminated irrigation water, and not the produce itself, may be the cause of the outbreak," she said.