Recently, MRSA has been found in horses and in persons who take care of them (4). Human carriage has also been linked to colonized companion cats and dogs (5,6). While Lee et al. (7) reported an MRSA isolation frequency of 0.6% in major food animals, but did not find MRSA in 469 samples from pigs, Armand-Lefevre et al. (8) described S. aureus (methicillin-susceptible and -resistant) carriage among pigs and pig farmers. Although the authors showed that both farmers and pigs carried methicillin-sensitive S. aureus and MRSA and that both groups shared certain multilocus sequence typing, the isolates came from separate, nonrelated collections.
Here we demonstrate transmission of MRSA between an animal and human (pig and pig farmer), between family members (pig farmers and their families), and between a nurse and patient in the hospital. The unexpected high frequency of MRSA among the group of regional pig farmers (>760× higher than in the general Dutch population) indicates that their profession might put them at risk for MRSA colonization. Overall, we found 3 different MRSA strains, including a new spa-type. Therefore, we expect that multiple strains are present in the pig population and the pig farmers. The strain with spa-type t108 appears to be more prevalent and widespread, given that the strain spread from animal to human, between family members, between patient and nurse, and among pig farmers from different regions.
Further research on a larger scale is needed to see if these observations hold true in other regions. If so, pig farming poses a significant risk factor for MRSA carriage in humans that warrants screening wherever pig farmers or their family members are admitted to a hospital.
Dr Voss is a consultant microbiologist and head of infection control at the Canisius-Wilhelmina Hospital and professor of infection control at the Radboud University Medical Centre. His primary research interests are nosocomial infections, including multidrug-resistant nosocomial pathogens such as MRSA.