In the Journals

Pig farmers at greater risk for MDR-S. aureus

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May 6, 2015

Pig farmers are six times more likely to carry multidrug-resistant Staphylococcus aureus than those without current swine exposure, according to research published in Clinical Infectious Diseases.

“This finding suggests that individuals with livestock contact may have a high prevalence of exposure to, and potentially infection with, antibiotic-resistant S. aureus strains, including [livestock-associated Staphylococcus aureus (LA-SA)] strains,” Tara C. Smith, PhD, of Kent State University’s College of Public Health, and colleagues wrote.

Smith and colleagues conducted a prospective study of 1,342 Iowans, including individuals with livestock contact and a community-based comparison group. Nasal and throat swabs were collected to determine colonization at enrollment, and skin infection swabs were assessed for S. aureus over 17 months, the researchers wrote. Outcomes included carriage of S. aureus, MRSA, tetracycline-resistant S. aureus (TRSA), multidrug-resistant S. aureus (MDRSA), and LA-SA.

Tara C. Smith

Of the total participants, 26.2% (95% CI, 23.8-28.6) carried S. aureus in their nose (16%), throat (4%) or both (6.1%). Individuals with current swine exposure were significantly more likely to carry S. aureus (prevalence ratio = 1.8; 95% CI, 1.4-2.2); TRSA (PR = 8.4; 95% CI, 5.6-12.6); MDRSA (PR = 6.1; 95% CI, 3.8-10); and LA-SA (PR = 5.8; 95% CI, 3.9-8.4) than those without exposure. Sixty-seven people reported skin infections for an incidence rate of 6.6 (95% CI, 4.9-8.9) per 1,000 person-months, according to data.

“Studies from the Netherlands and Germany have reported that LA-SA colonization depends strongly on direct exposure to swine. Our results provide further support for this conclusion,” the investigators wrote.

Smith and colleagues said their study was limited because most farmers were owners and operators of comparatively small family farms, rather than highly exposed livestock confinement workers, as were sampled in a U.S. study published in 2013. As a result, they said the cohort was most likely at the low end of MRSA prevalence. Normally, it has been associated with greater density and pig exposure.

Staphylococcus aureus colonization in humans is difficult to prevent; a third of Americans carry [methicillin-susceptible S. aureus (MSSA)] and 1.5% carry MRSA,” the researchers wrote. “No licensed vaccine against S. aureus exists for humans or animals. There is no method to decolonize animals that carry S. aureus.

As such, occupational exposure to livestock should be considered a significant risk factor when examining S. aureus colonization or treating infections in rural areas.” – by David Jwanier

Disclosure: The researchers report no relevant financial disclosures.