Professor Margaret Carrel quoted in Des Moines Register article.

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Presence of drug-resistant bacteria found far higher near big hog lots

Rural Iowans who live near large hog confinement operations are nearly three times more likely to carry a dangerous type of bacteria than those who live farther from the farms, a new study suggests.

However, the study’s authors and an outside expert cautioned that the research doesn’t prove the antibiotic-resistant bacteria found in the residents came from farms. The study also didn’t consider whether the people carrying the bacteria worked inside hog confinement facilities, where such bugs are a known risk, or if they simply lived nearby.

A hog industry critic said the results add to evidence that confinement operations should curb their broad use of antibiotic medications.

The study considered 1,036 rural residents who sought treatment at the Veterans Affairs Medical Center in Iowa City from 2009 through 2011. All of the patients had their noses swabbed for presence of a type of bacteria known as MRSA, or methicillin-resistant Staphylococcus aureus. The tests came up positive in 119 of the patients, or nearly 7 percent.

The researchers, who work for the VA and the University of Iowa, found the risk was nearly triple for those who lived within a mile of hog confinements that housed the equivalent of 2,500 or more adult animals.

Margaret Carrel, a University of Iowa geography professor who was the study’s lead author, said the people who had MRSA in their noses weren’t necessarily sickened by the germs. The VA hospital tests all incoming patients for the bacteria, so its staff can guard against a spread of the bugs to other patients.

MRSA bacteria are seen as a growing threat, because they can cause deadly infections that resist treatment with antibiotic drugs.

The Iowa study is being published in the February edition of the journal Infection Control and Hospital Epidemiology, and it already is available online. The paper has gained national attention in Wired magazine. Livestock confinement opponents are pointing to it as evidence that new regulations are needed.

However, Carrel noted that the paper had several caveats. For one thing, she said, the VA did not test the bacteria to see whether they were a strain commonly found in hog confinements or whether they might have come from other common sources in the community.

“You can get it off an ATM or a mailbox,” she said.

Peter Davies, a swine health expert at the University of Minnesota, said the study’s limitations are significant. Davies, who contacted the Register at the request of the National Pork Board, said it’s well-established that people who work in livestock facilities are more likely to pick up many kinds of bacteria, including MRSA strains. They sometimes can spread those bugs to people in their families. He said the inclusion of a few such people among the affected VA patients could throw off the study’s conclusions.

“The whole effect that they see may have little to do with living near a swine farm and everything to do with living on a swine farm or working on a swine farm,” he said.

Davies said that using the new study’s data to conclude that living near a hog confinement raises the risk of MRSA infection would be like touting a correlation between coffee consumption and lung cancer without checking to see if the coffee drinkers also smoke cigarettes.

But a hog confinement critic said the study adds to concerns about the industry’s practices. David Wallinga, a Minnesota physician who directs the national group Healthy Food Action, said confinement operations crowd together thousands of animals with tons of manure and expose them to huge amounts of antibiotics.

“Those are the perfect conditions for breeding these bacteria,” he said.

The bacteria that survive the antibiotics reproduce, trade genes and develop new populations that are harder to kill, he said.

Wallinga noted a federal report last year estimated that resistant-bacteria infections kill 23,000 Americans per year and contribute to many more deaths. He said the Iowa study should give critics more reason to demand limits on antibiotic use by livestock farmers. Wallinga also said people who live near large livestock confinements should inform their physicians before they enter a hospital, so they can be tested for the bacteria.

Carrel, the study’s lead author, agreed with Davies that the study doesn’t prove living near a hog farm increases the risk of picking up MRSA bacteria.

However, she said, it’s unusual to find a tripled risk among one group of people when compared with another.

“It suggests that further work needs to be done” on the research, she said.