Recent antibiotic use is a well documented risk factor for infection or colonisation with resistant pathogens.1^–7 Despite this recognition, unnecessary antibiotic prescribing remains common. In the United States more than a fifth of all antibiotic prescriptions for children and adults are written for upper respiratory tract infections or bronchitis, conditions that are almost always viral. 8 9 Similar rates of unnecessary antibiotic use have been described in Britain.10 These findings are consistent with results from focus groups among doctors, in which participants have estimated that 10% to 50% of outpatient antibiotic prescriptions are unnecessary.11

Only limited data are available to evaluate whether reducing antibiotic prescribing will reduce the spread of resistance. In Finland the proportion of group A streptococcal infections resistant to macrolides was nearly halved after a successful campaign to reduce the use of macrolide antibiotics.12 A cross sectional survey in Iceland found that carriage of penicillin resistant pneumococci was strongly associated with both individual and community-wide levels of antimicrobial use,13 and there is some evidence that an intervention programme has decreased the proportion of pneumococcal infections caused by penicillin resistantstrains.14