Does nasal colonization with Methicillin-resistant Staphylococcus aureus (MRSA) in pig farmers persist after holidays from pig exposure?

Background: In Germany, it has been reported that up to 86% of pig farmers are colonized with Methicillin-resistant Staphylococcus aureus (MRSA) in the nares, at least intermittently. However, little is known about the long-term persistence of colonization, especially when the farmers do not have daily contact to pigs. Here, we analyzed whether an absence from work during the summer holidays had an impact on nasal MRSA colonization rates of pig farmers. Method: Farmers with daily exposure to pigs during their work routine provided nasal swabs taken at the last three days before their summer leave 2010 and three additional swabs obtained at the first three days after return to work. Every first MRSA isolate was characterized using sequence-based typing of the S. aureus protein A gene (spa). Results: Among 35 farmers screened, the length of the summer leave was 14d for two farmers. MRSA was detected in at least one swab from 27 farmers (77%). From these, 16 (59%) were tested positive in all six swabs obtained before and after absence from work; three famers (9%) were tested positive before and negative in all three swabs obtained after the holidays; seven (20%) were tested negative in the swab obtained on the first day after return. One farmer (4%) was tested MRSA negative in all swabs before the leave and positive in all swabs after return from the holidays. The distribution of spa types was t011 (63%), t034 (22%), t108 (7%), t1197 and t1451 (each 4%). Conclusion: We confirmed a high rate of intermittent MRSA carriage (77%) among German pig farmers. Mostly, holidays did not have an impact on colonization. Only 14% of the farmers lost MRSA during their leave and remained negative for three days after return.