[Adamantane resistance among seasonal influenza A viruses between January to October in Guangzhou, 2009].

Objective: To study the prevalence of adamantane-resistance among influenza A viruses isolated from Guangzhou between January and October in 2009, and to provide more information for clinical usage of adamantane drugs.

Methods: Totally 311 influenza A strains isolated from 6 hospitals in Guangzhou between January and October in 2009 were selected, and the MP gene of all 311 strains (159 strains of H1 subtype, 152 strains of H3 subtype) was sequenced. The susceptibility of viruses to rimantadine was assayed by biological methods in cells.

Result: A hundred and forty-eight strains of influenza A (H1) viruses (93.1%, 148/159) were resistant to the adamantanes, and all the 152 influenza A (H3) viruses were resistant to the adamantanes. An amino acid substitution S31N was found in most of the strains except 1 strain with double mutation V27A/S31N. Furthermore, the M gene of influenza A (H1) viruses was divided into genotype B (human) (97/159) and genotype F (European and Australian birds, 62/159), while the M gene of influenza A (H3) viruses was genotype B (human) (152/152).

Conclusion: Resistance rate of seasonal influenza A viruses isolated from Guangzhou was high. The MP gene of influenza A (H1) may be replaced by a gene from European and Australian birds through a reassortment event.