Objective: To study the prevalence of oseltamivir-resistance among pandemic A (H1N1)2009 viruses isolated from patients in Guangzhou between 2009 and 2011, and to provide more information for clinical usage of oseltamivir.
Methods: Totally 192 pandemic A (H1N1)2009 viruses isolated from patients in Guangzhou between July 2009 and April 2011 were studies. The HA and NA genes of all strains were sequenced to reveal the evolution of viruses, and the susceptibility of viruses to oseltamivir was tested in vitro.
Results: One strain with a S247N mutation of the NA gene, which would make the virus resistant to oseltamivir, was found. The susceptibility (IC)50 of this viral strain to oseltamivir was 0.45 nmol/L, 2.5 times lower as compared to the wild-type strains. Phylogenetic analysis showed that this virus was not prevalent in Guangzhou from 2009-2011, and was not located in the same branch with the strains being epidemic in Australia and Singapore during the early seasons of 2011.
Conclusion: The resistance rate of pandemic A(H1N1)2009 viruses isolated from Guangzhou to oseltamivir was low, but surveillance on resistant strains needs to be strengthened to control resistant viruses imported from abroad.