Outpatient influenza antiviral prescription trends with influenza-like illness in the USA, 2008-2010.

The 2009 novel H1N1 influenza A virus (H1N1) became a global pandemic. Data on antiviral prescriptions by location from 2008 to 2010 have not been reported. The purpose of this study was to assess antiviral geographic trends and correlation with influenza-like illness (ILI) over 3 years. Percent of outpatient ILI visits and antiviral prescriptions from 1 January 2008 to 31 December 2010 were included. Linear regression was used to assess correlation. In total, 14 million antivirals were dispensed during this period. A 115% increase was observed in 2009 compared with prescriptions dispensed in 2008, and an 84% decrease was observed in 2010 compared with 2009. The rate of antivirals was 1.32 prescriptions/100 persons in 2008, 2.85/100 persons in 2009 and 0.435/100 persons in 2010. 2009 regional growth was observed in most states and was highest in the West (293%) and the Northeast (272%). A positive correlation was observed between antivirals and ILI visits (R(2)=0.7853; P<0.0001). With the 2009 H1N1 pandemic, antivirals increased compared with 2008 or 2010. Without the concern of H1N1, antivirals decreased in 2010 to levels lower than 2008. Geographic trends were also observed, which may be a result of the different intensity of influenza transmission and difference practice patterns. ILI diagnoses correlate with influenza antiviral prescription use in the USA.