Influenza antiviral prescribing practices during the 2007-08 and 2008-09 influenza seasons in the setting of increased resistance to oseltamivir among circulating influenza viruses.

INTRODUCTION

In December 2008, new interim guidelines on the use of influenza antiviral agents were released in response to a high prevalence of circulating oseltamivir-resistant seasonal influenza A(H1N1) and adamantane-resistant influenza A(H3N2) viruses. Zanamivir, oseltamivir +/- an adamantane, or oseltamivir was recommended, depending on virus type, subtype, and local surveillance data.

MATERIALS AND METHODS

Information about antiviral prescribing practices among IDSA Emerging Infections Network (EIN) members was obtained using two web-based questionnaires; one in January 2009 regarding the prior 2007-08 influenza season and one in April 2009 (prepandemic), regarding the concurrent 2008-09 season.

RESULTS

In the 2007-08 survey, 646 (52%) of 1249 EIN members responded and in the 2008-09 season survey, 350 (27%) of 1281 responded. In 2008-09 vs. 2007-08: 59% vs. 69% prescribed or recommended antivirals for treatment (p<.0001); 48% vs. 80% prescribed oseltamivir alone and 39% vs. 10% prescribed zanamivir alone (p<.0001 for both). During 2008-09 28% reported treating fewer patients compared with 2007-08; 42% felt antivirals were less effective due to resistance and 40% felt patients had less severe illness. During 2008-09, 42% of respondents reported difficulty providing zanamivir to patients vs. 5% for oseltamivir (p<.0001). Only 11% of respondents could test for influenza A subtype. During both seasons, ~55% used local surveillance data to make treatment decisions.

DISCUSSION

A mild winter influenza season, difficulty obtaining recommended agents, and lack of access to subtype diagnosis and surveillance data may have contributed to reduced antiviral use during 2008-09.