Surveillance of Resistance to Adamantanes among Influenza A(H3N2) and A(H1N1) Viruses Isolated Worldwide

Varough M. Deyde, etc.,al. Surveillance of Resistance to Adamantanes among Influenza A(H3N2) and A(H1N1) Viruses Isolated Worldwide. The Journal of Infectious Diseases 2007;196:249
submited by kickingbird at Jun, 21, 2007 6:3 AM from The Journal of Infectious Diseases 2007;196:249

Our previous reports demonstratedan alarming increase inresistance to adamantanes amonginfluenza A(H3N2) viruses isolatedin 2001–2005. To continuemonitoring drug resistance, weconducted a comprehensive analysisof influenza A(H3N2) andA(H1N1) viruses isolated globallyin 2005–2006. The resultsobtained by pyrosequencing indicatethat 96.4% (n =761) of A(H3N2) virusescirculating in the UnitedStates were adamantane resistant.Drug resistance has reached100% among isolates fromsome Asian countries. Analysisof correlation between theappearance of drug resistanceand the evolutionary pathwayof the hemagglutinin (HA)gene suggests at least2 separate introductions ofresistance into circulating populationsthat gave rise toidentifiable subclades. It alsoindicates that resistant A(H3N2)viruses may have emergedin Asia in late2001. Among A(H1N1) virusesisolated worldwide, resistance reached15.5% in 2005–2006; inthe United States alone,it was 4.0%. Phylogeneticanalysis of the HAand M genes indicatesthat the acquisition ofresistance in A(H1N1) virusescan be linked toa specific genetic groupand was not aresult of reassortment betweenA(H3N2) and A(H1N1) viruses.The results of thestudy highlight the necessityof close monitoring ofresistance to existing antiviralsas wells as theneed for new therapeutics.