Living near livestock populations increases the risk of exposure to certain strains of Methicillin-Resistant Staphylococcus Aureus—also known as MRSA—even for residents who do not handle livestock.
American and Dutch researchers led by professor Beth Feingold, a visiting scholar at the Duke Global Health Institute from Johns Hopkins University, discovered that livestock-related strains of MRSA spread easily through areas of high livestock density, regardless of individuals’ contact with livestock. The study was conducted by analyzing cases of MRSA reported in the Netherlands, a country with relatively high livestock density per capita in rural areas. The easy spread of bacteria without direct contact is unusual and deserves further research, the study’s authors said.
“People living in areas of high livestock density have higher risk, even after accounting for known risk factors like direct contact with animals,” Feingold wrote in an email Wednesday. “It is interesting that most studies have looked only at direct contact with animals as a risk factor, and have not considered the potential for secondary transmission.”
According to the report published in the Centers for Disease Control and Prevention publication Emerging Infectious Diseases, doubling the density of various livestock increases a person’s odds of carrying livestock associated MRSA over another kind by 20 to 75 percent.
The natural presence of staph bacteria in the nose and sometimes on the skin does not normally cause problems. However, open wounds can sometimes allow the bacteria to enter the body and cause a staph infection. Normal strains of staph are frequently treated with antibiotics. MRSA strains, however, are resistant to traditional courses of treatment and can lead to far more severe infections. It is possible for carriers of MRSA to spread it to others or become infected themselves.
This study analyzed whether or not individuals carried livestock associated MRSA and attempted to link the carriage with proximity to livestock populations, not just livestock contact.
“Non-typable MRSA was, in [a] 2007 paper, shown to be statistically associated with people who lived in rural areas and who worked with livestock—thus it was later known as livestock associated MRSA,” Feingold said. “I was interested in seeing if there was a trued geographical or spatial connection between the two.”
Working with various other researchers from Johns Hopkins and Jan Kluytmans, a professor at VU University Medical Center in the Netherlands, Feingold discovered that mere proximity was sufficient to increase the odds of carrying and thus potentially being infected by MRSA.
Yet person-to-person contact fails to explain the spread of the bacteria through local populations.
“A study among veterinarian field workers found that after short-term occupational exposure to pigs, 17 percent of them carried MRSA. However, more than 90 percent of those lost this carriage the next day,” the study said.
Feingold said there is reason for further investigation into how these bacteria spread. Although the study does not necessarily indicate increased risk of MRSA carriage, it does indicate that livestock associated MRSA is far more likely to be carried by individuals living in livestock-dense regions than any other type of staph. Considering the absence of easily explained modes of transmission, this trend raises questions relating to public health, as well as whether other diseases exhibit similar geographic trends.
“The next steps should be research to answer the question, ‘Do we see similar relationships everywhere?’” Feingold said.
The data suggest that MRSA may be transmitted by some other medium that is not yet fully understood.
“We hope that our study helps spur other research to investigate the exact nature of how people who may not have direct contact are getting exposed, especially in light of the fact that most research has demonstrated that livestock associated strains are not easily transmitted from person to person—this is only a very small piece of a puzzle.”