WOOSTER, Ohio -- Farmers, especially dairy farmers, could be putting their families at risk if they're not cautious about cleanliness, according to a newly published Ohio State University study.
The study, "Differences in Listeria monocytogenes Contamination of Rural Ohio Residences With and Without Livestock" was published in the January 2010 issue of the journal Foodborne Pathogens and Disease.
For the study, researchers made four visits each to 52 rural households; half of the households were operating a dairy, sheep or beef cattle farm. During the visits, researchers collected samples and tested them for Listeria monocytogenes, a food-borne disease pathogen prevalent throughout nature.
Although L. monocytogenes is widespread, it rarely causes illness -- but when it does, the illness can be severe. In fact, the Food and Drug Administration estimates that there are only about 1,600 cases of listeriosis, the disease caused by L. monocytogenes, in the U.S. per year, but about one-quarter of those cases are fatal. Most at risk are fetuses of pregnant women, newborns, as well as immuno-compromised individuals and the elderly.
"Although we focused on looking for Listeria, we actually were using it as a marker for any type of pathogen," said Jeffrey LeJeune, associate professor in the Food Animal Health Research Program of Ohio State's Ohio Agricultural Research and Development Center. "We know that Listeria survives really well in the environment, but if it's in the home, that's an indication that there could be other pathogens getting into the home, too."
Listeriosis is most often linked with contaminated lunch meat, hot dogs and especially milk and dairy products that are unpasteurized.
"One of our goals was to see if we could shed light on how Listeria enters homes, and if ruminant-farm households were at greater risk for contamination," said LeJeune, who is also a food safety specialist with Ohio State University Extension.
For this study, researchers took samples of food items most likely to be contaminated with L. monocytogenes, including dairy products, leftovers, and ready-to-eat deli products. If one of those items was unavailable, they substituted an item of fresh produce for sampling.
They also collected samples from various surfaces throughout the homes, including refrigerators, kitchen sinks, washing machines, and the bottoms of shoes or boots. In farm households, they also took samples of work gloves; in non-farm households, they took samples from kitchen counters. In addition, the researchers collected samples of both human and farm-animal feces, since the organism can be found in the stools of infected animals and people.
In all, 1,779 samples were collected throughout the study. Forty-seven of these samples were positive for L. monocytogenes: 20 samples from shoes; nine from animal fecal samples; seven from food items; six from work gloves; three from kitchen sinks; and two from washing machines.
Results showed that L. monocytogenes was much more likely to be isolated from farm households than non-farm rural homes. In fact, the chance of detecting L. monocytogenes at farm households was more than twice as great (54 percent chance) than at non-farm rural households (23 percent chance), primarily because of the fecal samples taken from farm animals. Even more telling was when farm-animal samples and food samples (which may have been contaminated at the store or otherwise outside of the household) were excluded from analysis: Then, the odds of detecting L. monocytogenes in the home were 5.6 times higher at farm households than at non-farm rural homes.
In one farm household, a no-bake cookie tested positively for Listeria of the same molecular fingerprint as was found in one of the farm animals, pointing a finger directly at the animals on the farm as the source of contamination.
"That was one of our most important findings," said co-investigator Lydia Medeiros, food safety researcher with OARDC and Ohio State University Extension. "To show an actual DNA link between Listeria in the farm animals to Listeria found in food in the house -- that's significant. It's like finding a needle in a haystack."
Medeiros, who is also a professor of human nutrition in the College of Education and Human Ecology, said the study's findings carry a strong message for livestock farmers.
"Farmers working with animals, particularly dairy cattle, need to take precautions not to carry contamination into the household," she said. "Clothing and shoes worn outside need to stay outside. And, since we found contamination on two washing machines, it may be a good idea to have a separate laundry area just for work clothes."
LeJeune added that, although Listeria showed up more in farm households than non-farm homes, it did appear in both.
"To me, that means that hygiene is critical for everyone," LeJeune said. "Anyone can bring these pathogens into the home -- on the bottoms of their shoes, for example. Then the children might drop their backpacks on the floor, and later put the backpacks on a kitchen counter or kitchen table, where they are also eating lunch. That's just a bad combination."
The study's primary author was Ann Kersting, one of LeJeune's graduate students who worked on the study as part of her dissertation.
Jeff LeJeune, Food Animal Health Research Program
Lydia Medeiros, Human Nutrition