Effect of antibiotic prescribing in primary care on meticillin-resistant Staphylococcus aureus carriage in community-resident adults: a controlled observational study.

The objectives of this study were to investigate the relationship between primary care antibiotics prescribed within 2 months and 12 months and the carriage of meticillin-resistant Staphylococcus aureus (MRSA) in nasal flora from a large representative sample of community-resident adults. S. aureus isolates were obtained from nasal samples submitted by UK resident adults aged ≥ 16 years registered with 12 general practices in the former Avon and Gloucestershire health authority areas. Individual-level antibiotic exposure data during the 12 months prior to providing the samples were collected from the primary care electronic records. MRSA status was determined by measuring resistance to cefoxitin. In total, 6937 adults were invited to take part, of whom 5917 returned a nasal sample. S. aureus was identified in 946 samples and a total of 761 participants consented to primary care record review and had complete data for the analyses. There was no evidence of an association between any antibiotic in the previous 2 months and MRSA isolation, with an adjusted odds ratio (aOR) of 1.33 [95% confidence interval (CI) 0.12-15; P=0.8]. There was a suggestion of an association between any antibiotic use in the previous 12 months and MRSA, with an aOR of 2.45 (95% CI 0.95-6.3; P=0.06). In conclusion, there is a suggestion that antibiotics prescribed within 12 months is associated with the carriage of MRSA, but not within 2 months, although the 2-month analysis had fewer data subjects and was therefore underpowered to detect this association. A larger study would be able to clarify these associations further.