Oseltamivir-resistant influenza A(H1N1) viruses in south of France, 2007/2009

In 2007/2008, among 374 A(H1N1) isolates tested, 38% were resistant to OC with a mean IC50 of 564 ± 357 nM. The mean Km of OC-sensitive isolates (H275) was significantly lower (22.6 ± 4.7 μM) than the Km of previous reference strains (44.9 ± 5 μM) and the mean Km of the OC-resistant isolates (Y275) (37.2 ± 7.7 μM). The combination of different amino acid mutations in N1 particularly the D344N could explain the higher NA affinity of A/Brisbane/59/2007 related variants compared to the previous A(H1N1) strains and the H275Y mutation allowed to retrieve Km values near 40 μM.