Does antibiotic exposure increase the risk of methicillin-resistant Staphylococcus aureus (MRSA) isolation?: A systematic review and meta-analysis

Background: Current evidence does not provide a clear definition of the association between methicillin-resistant Staphylococcus aureus (MRSA) isolation and previous antibiotic use. A systematic review was performed to determine whether antibiotic exposure is a risk factor for the isolation of MRSA. Methods: MEDLINE and EMBASE databases were searched to identify studies published between 1976 and 2007 on the role of antibiotics as a risk factor for MRSA isolation in adult patients. The outcome of interest was MRSA isolation. Summary statistics were risk ratios (RR) comparing MRSA-positive patients to those without S. aureus isolation or with methicillin-susceptible S. aureus isolation. Results: Seventy-six studies, including a total of 24 230 patients, met the inclusion criteria. Antibiotic exposure was determined in the 126 +/- 184 (mean +/- SD) days preceding MRSA isolation. The risk of acquiring MRSA was increased by 1.8-fold [95% confidence interval (CI), 1.7-1.9; P < 0.001] in patients who had taken antibiotics. The RR for single classes of antibiotics was 3 (95% CI, 2.5-3.5) for quinolones, 2.9 (95% CI, 2.4-3.5) for glycopeptides, 2.2 (95% CI, 1.7-2.9) for cephalosporins and 1.9 (95% CI, 1.7-2.2) for other beta-lactams. Significant heterogeneity was detected among studies. A regression analysis revealed that the heterogeneity was linked to the length of time in which antibiotic exposure was detected before MRSA isolation (more or less than 180 days). Conclusions: This meta-analysis shows a clear association between exposure to antibiotics and MRSA isolation. This information may be useful for researchers in designing future studies and for policy decision-making on the appropriate management of antibiotic therapies.