Use of oseltamivir in 12 European countries between 2002 and 2007 – lack of association with the appearance of oseltamivir-resistant influenza A(H1N1) viruses

Variable levels of oseltamivir resistance among seasonal influenza A(H1N1) isolates have been reported in Europe during the 2007-8 northern Hemisphere influenza season. It has been questioned whether oseltamivir use could have driven the emergence and predominance of resistant viruses. This study aimed at describing the levels of use of oseltamivir in 12 European Union (EU) Member States and European Economic Area (EEA)/European Free Trade Area (EFTA) countries. The data were converted into prescription rates and compared with the national proportions of resistant influenza A(H1N1) viruses through regression analysis. Overall use of oseltamivir in European countries between 2002 and 2007 was low compared to e.g. the use in Japan. High variability between the countries and over time was observed. In eight of the 12 countries, there was a peak of prescriptions in 2005, coinciding with concerns about a perceived threat from an influenza pandemic which might have lead to personal stockpiling. Ecological comparison between national levels of use of oseltamivir in 2007 and the proportions of A(H1N1) viruses that were resistant to oseltamivir showed no statistical association. In conclusion, our results do not support the hypothesis that the emergence and persistence of these viruses in 2007-8 was related to the levels of use of oseltamivir in Europe. Further investigation is needed to elucidate the reasons for different level of use between the countries.