Hog Workers More Likely to Carry Staphylococcus aureus Bacteria

Animal handlers and farm workers are known to be exposed to certain zoonotic diseases spread from animals to humans, and now a new study examines the risk that industrial hog workers face from livestock-associated Staphylococcus aureus.

About 30% of people carry Staphylococcus aureus, or staph, bacteria in their noses, according to the Centers for Disease Control and Prevention (CDC). While many of these carriers do not develop symptoms or active staph infections, they can spread the bacteria to others who can become infected. Methicillin-resistant S. aureus (MRSA) and other forms of multidrug-resistant S. aureus (MDRSA) most commonly cause skin and soft tissue infections (SSTI) which are resistant to several antibiotic drugs and notably hard to treat. Such infections cause skin bumps that are red, swollen, painful, full of pus, and can be accompanied by a fever. MRSA is one of the major causes of healthcare-associated infections and with more than 80,000 infections and 11,000 deaths each year, is considered one of the CDC’s biggest drug-resistant threats, but hospitals are not the only source for these infections.

S. aureus infections from contact with livestock have been observed around the world, and a largescale study last year on individuals with livestock contact found that swine workers are six times more likely to carry antibiotic-resistant staph bacteria and at are higher risk for developing staph infections. A recent study led by researchers at the Johns Hopkins University Bloomberg School of Public Health looked at the link between S. aureus carriage among industrial hog operation workers and SSTI symptoms in those workers and their household members. Their paper was recently published in the open access journal PLOS ONE.

The study’s authors note that it is difficult to investigate the associations between livestock-associated S. aureus nasal carriage and SSTI in clinical settings because many livestock workers lack regular access to medical care and because people with SSTI symptoms are not typically given a nasal screening for S. aureus. Their investigation involved 108 North Carolina hog workers and 80 members of their households who agreed to let researchers swab their noses to see if they carried S. aureus bacteria in their noses. Study participants also responded to a questionnaire and were shown images of staph skin infections to determine if they’d had such infections within the previous three months. Researchers collected all data from October 2013 to February 2014.

From the nasal swabs collected, the team found that 44% of the workers and 39% of the members of their households carried S. aureus bacteria in their noses. In addition, 6% of the workers and 11% of the children in their households had experience recent SSTI. Those workers carrying S. aureus in their noses were five times more likely to have had a recent SSTI than those who were not carriers of the bacteria.

Along with these findings, the researchers analyzed the S. aureus isolates for antibiotic susceptibility and found MRSA in only one worker and MDRSA in the 21 workers and eight of their household members. "Before this study, we knew that many hog workers were carrying livestock-associated and multidrug-resistant Staphylococcus aureus strains in their noses, but we didn't know what that meant in terms of worker health," said study leader Johns Hopkins University assistant professor Christopher D. Heaney, PhD, in a recent press release about the investigation. "It wasn't clear whether hog workers carrying these bacteria might be at increased risk of infection. This study suggests that carrying these bacteria may not always be harmless to humans."

While the study had limitations, such as its relatively small size and the potential for missed S. aureus carriers from the lack of swabs taken from other body sites, the authors note that livestock workers have an occupational risk for staph infections and may be particularly vulnerable due to lacking access to healthcare. The authors call for additional research to better understand the risk faced by hog operation workers.