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 <7d for two farmers, 7-14d for 22 and >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. Introduction Methicillin-resistant Staphylococcus aureus (MRSA) has been reported to colonize livestock (pigs, cattle, poultry) in the most European countries. In Germany, up to 70% of all pig farms [1, 2] are affected. Among the MRSA from livestock reservoirs, isolates belonging to one particular clonal complex (CC), CC398 as defined by multilocus sequence typing (MLST), are predominant and account for more than 90% of all isolated strains [1]. Moreover, it has been described that MRSA CC398 is frequently transmitted to persons with a direct contact to the animals leading to colonization rates of up to 86% among farmers from MRSA positive units [3]. However, a Dutch study has recently shown that persons with occupational exposure to the animals might be colonized only inpersistently. Field workers with a short-term exposure up to 3h daily were positive directly after their visit on a pig farm. But 94% appeared negative when a second nasal swab was collected 24 hours later [4]. Currently, little is known about the MRSA colonization dynamics of persons with a direct and regular contact to livestock. Therefore we invastigated whether an absence from the pig farm during the summer holidays had an impact on MRSA carrier rates among German pig farmers. Material and Methods Farmers in the German part of the Dutch-German border region (North Rhine-Westphalia, Lower Saxony) with daily exposure to pigs provided nasal swabs taken during the last three days before their summer leave 2010. Three additional swabs were obtained during the first three days after return to work. All swabs were obtained from the individual farmers in the morning before their first contact to the animals. All nasal swabs were streaked directly onto MRSA-ID (bioMérieux)