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

Abstract

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.