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During October 2010-July 2011, 1.0% of pandemic (H1N1) 2009 viruses in the United States were oseltamivir resistant, compared with 0.5% during the 2009-10 influenza season. Of resistant viruses from 2010-11 and 2009-10, 26% and 89%, respectively, were from persons exposed to oseltamivir before specimen collection. Findings suggest limited community transmission of oseltamivir-resistant virus.

The need for effective influenza antiviral susceptibility surveillance methods has increased due to the emergence of near-universal adamantane resistance in influenza A/H3N2 viruses during the 2005-2006 season and the appearance of oseltamivir resistance in the influenza A/H1N1 virus subtype during the 2007-2008 season. The two classes of influenza antivirals, the neuraminidase inhibitors (NAIs) and the adamantanes, are well characterized, as are many mutations that can confer resistance to these drugs. Adamantane resistance is imparted mainly by a S31N mutation in the matrix gene, while NAI resistance can result from a number of mutations in the neuraminidase gene. During the 2007-2008 season, a neuraminidase mutation (H274Y) conferring resistance to the NAI oseltamivir emerged worldwide in the A/H1N1 virus subtype. Surveillance methodology and data from New York (NY) and Wisconsin (WI) for the 2006-2007 and 2007-2008 influenza seasons are presented. We used an existing pyrosequencing method (R. A. Bright et al., Lancet 366:1175-1181, 2005) and a modified version of this method for detection of adamantane resistance mutations. For NAI resistance mutation detection, we used a mutation-specific pyrosequencing technique and developed a neuraminidase gene dideoxy sequencing method. Adamantane resistance in the A/H3N2 virus samples was 100% for 2007-2008, similar to the 99.8% resistance nationwide as reported by the CDC. Adamantane resistance was found in only 1.2% of NY and WI A/H1N1 virus samples, compared to that found in 10.8% of samples tested nationwide as reported by the CDC. Influenza A/H1N1 virus H274Y mutants were found in 11.1% of NY samples for 2007-2008, a level comparable to the 10.9% nationwide level reported by the CDC; in contrast, mutants were found in 17.4% of WI samples. These results indicate the need for regional influenza antiviral surveillance.

To assess whether the use of rapid influenza diagnostic tests (RIDTs) for long-term care facility (LTCF) residents with acute respiratory infection is associated with increased antiviral use and decreased health care utilization. Nonblinded, pragmatic, randomized controlled trial evaluating a 2-part intervention with modified case identification criteria and nursing staff–initiated collection of nasal swab specimen for on-site RIDT. Residents of 20 LTCFs in Wisconsin matched by bed capacity and geographic location and then randomized. Primary outcome measures, expressed as events per 1000 resident-weeks, included antiviral treatment courses, antiviral prophylaxis courses, total emergency department (ED) visits, ED visits for respiratory illness, total hospitalizations, hospitalizations for respiratory illness, hospital length of stay, total deaths, and deaths due to respiratory illness over 3 influenza seasons. Oseltamivir use for prophylaxis was higher at intervention LTCFs [2.6 vs 1.9 courses per 1000 person-weeks; rate ratio (RR) 1.38, 95% CI 1.24-1.54; P <.001]; rates of oseltamivir use for influenza treatment were not different. Rates of total ED visits (7.6 vs 9.8/1000 person-weeks; RR 0.78, 95% CI 0.64-0.92; P =.004), total hospitalizations (8.6 vs 11.0/1000 person-weeks; RR 0.79, 95% CI 0.67-0.93; P =.004), and hospital length of stay (35.6 days vs 55.5 days/1000 person-weeks; RR 0.64, 95% CI 0.0.59-0.69; P <.001) were lower at intervention as compared to control LTCFs. No significant differences were noted for respiratory-related ED visits or hospitalizations or in rates for all-cause or respiratory-associated mortality. The use of low threshold criteria to trigger nursing staff–initiated testing for influenza with RIDT resulted in increased prophylactic use of oseltamivir. There were significant reductions in the rates of all-cause ED visits (22% decline), hospitalizations (21% decline), and hospital length of stay (36% decline) across 3 combined influenza seasons. No significant differences were noted in respiratory-associated and all-cause deaths between intervention and control sites. [ABSTRACT FROM AUTHOR]