Trends and seasonal variation in outpatient antibiotic prescription rates in the United States, 2006 to 2010.

Antibiotic-resistant bacteria are an increasing threat to the effectiveness of antibiotics. The majority of antibiotics are prescribed in primary care settings for upper respiratory tract infections. The purpose of this study was to describe seasonal trends in outpatient antibiotic prescriptions (Rx) in the United States over a 5-year period. This study was a retrospective, cross-sectional observation of systemic antibiotic prescriptions in the outpatient setting from 2006 to 2010. Winter months were defined as the first and fourth quarters of the calendar year. Antibiotic prescribing rates were calculated (prescriptions/1,000 population) using annual U.S. Census Bureau population data. Over 1.34 billion antibiotic prescriptions were dispensed over the 5-year period. The antibiotic prescription (Rx) rate decreased from 892 Rx/1,000 population in 2006 to 867 Rx/1,000 population in 2010. Penicillins and macrolides were the primary antibiotic classes prescribed, but penicillin prescribing decreased while macrolide prescribing increased over the study period. Overall, antibiotic prescriptions were 24.5% higher in winter months than in the summer, with the largest difference (28.8%) in 2008 and the smallest (20.4%) in 2010. This seasonality was consistently drug class dependent, driven by 75% and 100% increases in penicillin and macrolide prescriptions, respectively, in the winter months. The mean outpatient antibiotic prescription rate decreased in the United States from 2006 to 2010. More antibiotic prescribing, predominately driven by the macrolide and penicillin classes, in the outpatient setting was observed in the winter months. Understanding annual variability in antibiotic use can assist with designing interventions to improve the judicious use of antibiotics.