Research has found that pig farm workers likely spread methicillin-resistant Staphylococcus aureus (MRSA) to swine in Norway. Scientists observed signs of the human-to-pig infection while working on a campaign to stamp out MRSA in Norway.
The researchers asserted that disease-prevention programs like Norway’s could reduce the spread of antibiotic-resistant bacteria, especially in countries with little or no import of live pigs, since farm workers could introduce the disease to pig herds.
Tracking and studying LA-MRSA
Epidemiologists identified three livestock associated-MRSA (LA-MRSA) outbreak clusters in Norway, wrote the researchers in the journal "Clinical Infectious Diseases." Those outbreaks affected 26 pig farms, two slaughterhouses and 36 humans. The study analyzed epidemiological data collected from the first discovery in 2013 until 2015.
Genetic evidence suggested that human transmission to three sow farms likely initiated the outbreaks. Secondary transmission to other pig farms then occurred, mainly through animal trade and via humans or vehicles.
The researchers performed genetic testing of bacterial isolates from all individuals identified with LA-MRSA since 2008, and they collected samples from all animals, people and pig farm environments that were affected by outbreaks in 2013 and 2014. These findings show that pig farm workers are the principal source for the introduction of LA-MRSA in Norwegian pig herds.
“MRSA rarely causes severe infections among otherwise healthy people but a rising incidence of MRSA in the population will contribute to an increased infection burden for vulnerable patients in the health services,” said study co-author Petter Elstrøm, researcher at the Norwegian Department of Antibiotic Resistance and Infection Prevention, in a press release.
LA-MRSA surveillance
Since 2014, the Norwegian Food Safety Authority and the Norwegian Veterinary Institute have continuously monitored all pig herds in Norway.
“Our strategy of slaughtering pig herds where LA-MRSA bacteria are detected plus farm disinfection was developed in a close collaboration between the authorities and swine industry,” said Elstrøm.
The strategy's goal has been to prevent LA-MRSA from being introduced and spread among Norwegian pig herds, thereby preventing pig herds from becoming a major source of MRSA infection to the general human population.
Scientists at the Norwegian Institute of Public Health believe the LA-MRSA strategy has been effective. Further transmission from animals or humans in the affected farms to the general population has not been detected by Norwegian authorities. Official recommendations about who should be tested for LA-MRSA before contact with livestock have been issued to prevent transmission from farm workers to pigs.
