Objective To investigate in children the association between antibacterial drugs and subsequent diagnosis of methicillin-resistant Staphylococcus aureus (MRSA) in the community.
Design Population-based case-control study in children 1 to 19 years of age.
Setting Primary care, General Practice Research Database, United Kingdom, 1994-2007.
Participants Cases were children who had MRSA diagnosed as outpatients, and controls were individually matched on age and practice, with the matched case's diagnosis date as the index date for both.
Main Exposures Antibacterial agents prescribed 180 to 30 days prior to the index date, excluding prescriptions 30 days before the index date to prevent protopathic bias.
Outcome Measures Rate ratios (RRs) estimated from the odds ratios of exposure in cases compared with controls using conditional logistic regression, adjusted for comorbid conditions, other prescription drug use, and hospitalization.
Results The rate of MRSA was 4.5 per 100 000 per year. Of 297 cases and 9357 controls, 52.5% and 13.6%, respectively, received antibacterial drug prescriptions during the 150-day exposure window. The adjusted RR with any antibacterial drug was 3.5 (95% confidence interval [CI], 2.6-4.8). The RRs increased with the number of prescriptions (2.2 [95% CI, 1.5-3.2], 3.3 [95% CI, 1.9-5.6], 11.0 [95% CI, 5.6-21.6], and 18.2 [95% CI, 9.4-35.4] for 1, 2, 3, and ≥4 prescriptions, respectively). The RR was particularly elevated for quinolones at 14.8 (95% CI, 3.9-55.8), with wide variation among antibacterial classes.
Conclusion While close to half of children were diagnosed as having MRSA in the community without prior antibacterial drugs, such agents are associated with a dose-dependent increased risk, concordant with findings in adults.