Objectives Determine the incidence and prevalence of nasal colonisation of swine veterinarians with S. aureus in the USA, and quantify associations between risks of S. aureus colonisation and infection and exposure to pigs.
Methods 1) Cross-sectional survey of swine veterinarians regarding general occupational health and safety. 2) Longitudinal bacteriological testing (nasal swabs) of 68 veterinarians sampled monthly for 18 months for S. aureus and MRSA carriage. Isolates are characterised of using spa typing (eGenomics and Ridom spa servers) and multilocus sequence typing. The veterinarians work in most major pig producing states of across the USA. Concurrent assessment of intensity of pig exposure, occurrence of skin and soft injuries, occurrence of S. aureus infections, and use of PPE is made monthly via survey.
Results Across the first 4 months of bacteriological testing, prevalence of both S. aureus (60–70%) and MRSA (7–10%) were above expected levels in the USA population (30%, 3% respectively). Prevalence is significantly higher in veterinarians sampled within 48 hours of pig contact than after longer periods. Three spa types (539/t034 - ST398; 2/t_unknown - ST 5; 1435/t337 - ST9 comprised 65% of all S. aureus isolates from swine veterinarians. The 3 spa/sequence types have been reported as ‘livestock associated’ MRSA in Europe (ST398), Asia (ST9) and North America (ST5), but the majority of isolates from US veterinarians were methicillin sensitive (MSSA). Although minor skin injuries have been a frequent occurrence (5% cumulative incidence monthly), clinical infections with MRSA or MSSA have not yet been reported.
Conclusions Swine veterinarians in the USA are frequently culture positive for S. aureus variants that are common in swine. Many exposure events appear to result in only transient colonisation. To date, risk of clinical S.aureus infection in this group appears to be modest, despite widespread exposure to the organisms and a high incidence of opportunity for infection via skin wounds.
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