Drug-resistant staph can cling to farm workers for days

Days after leaving the farm, agricultural workers can still tote farm-reared, drug-resistant Staphylococcus aureus in their noses. The pig-dwelling bacteria may cause infections in the workers and could put family and community members at risk, too.

In a two-week study, researchers led by epidemiologist Christopher Heaney of Johns Hopkins University collected nasal swabs from 22 hog farm workers in eastern North Carolina. Nineteen of the workers, or 86 percent, carried staph at some point during the study, and around half had a multidrug-resistant strain. That’s compared with only about a third of people in the general population who carry staph and only about 5 percent who harbor drug-resistant strains.

About half of the farm workers also consistently carried the germs throughout the study period, even if they left the farm for up to four days. Some earlier studies had suggested that staph bacteria hang around in workers’ noses only for about 24 hours. In general, the longer someone carries a germ, the greater their chances of getting sick or of transmitting it to others. The new results appear September 8 in Occupational & Environmental Medicine.

With limited data, the team can’t say how many workers went on to develop staph infections or whether the bacteria spread to other people. But the work provides important first steps toward answering those questions, Heaney says.

Industrial hog farms are a known source of drug-resistant staph, including methicillin-resistant Staphylococcus aureus, or MRSA. Staph naturally lives on pigs and because many modern farms use high levels of antibiotics, farms have long been feared to breed drug resistance. But epidemiologists and public health advocates lack enough data to say whether farms pose a health threat to workers and neighboring communities.

Collecting data on the health of farm laborers has been difficult because workers are often reluctant to participate in scientific studies, says epidemiologist Tara Smith of Kent State University in Ohio: Some may be undocumented immigrants and others may simply be afraid of backlash from employers. It’s also difficult to get people to repeatedly and consistently swab their noses for staph samples, even if they are interested in participating, she says.

For the new study, Heaney partnered with researchers and community advocates who work in eastern North Carolina, which has the highest density of pig farms in the United States. Members of the advocacy group Rural Empowerment Association for Community Help met with workers to explain the study and to anonymously enroll participants. “There’s never any names or addresses given out,” project manager Devon Hall says. “It’s a trust issue.”

Enrolled workers were healthy throughout the study and the majority worked more than 50 hours a week. Some worked with upwards of 5,000 hogs a day. The researchers collected 327 swabs after asking workers to swab their noses every morning and evening for seven days and again for one day a week later. This schedule allowed researchers to track which staph strains the workers picked up and how long they carried the microbes.

Half of the samples were multidrug resistant — immune to three or more drugs — and one worker carried MRSA throughout the study.  Most of the staph strains had telltale genetic signs of originating in farms, suggesting that the workers hadn’t picked up the germs elsewhere. Further genetic studies should help pin down the path of bacteria that may move between pigs and people, Smith says.