Table 2.
Summary of Influenza Viruses Possessing a Neuraminidase (NA) Substitution
| Virus ID | Amino acid substitution in NA | Subtype of virus | Age of patient, years | Date of sampling (day after beginning of treatment) | Proportion of viruses with substituted NA, %a | IC50 for oseltamivir,b nM |
|
| Parental virus | Mutant virus | ||||||
| 1 | Arg292Lys | H3N2 | 5 | 3 | 0 | 0.21 | 33,390 |
| 5 | 25 | 0.21 | 33,390 | ||||
| 2 | Arg292Lys | H3N2 | 9 | 3 | 0 | NTc | NT |
| 5 | 50 | NTc | NT | ||||
| 3 | Arg292Lys | H3N2 | 13 | 4 | 8 | NT | NT |
| 4 | His274Tyr | H1N1 | 4 | 5 | 8 | 1.63 | 1115 |
| 7 | 75 | 1.63 | 1115 | ||||
| 5 | His274Tyr | H1N1 | 9 | 4 | 16 | NT | NT |
| 6 | Glu119Val | H3N2 | 5 | 4 | 41 | 0.43 | 230 |
a
For each virus isolate, we analyzed the nucleotide sequences of the NA genes of at least 12 molecular clones and calculated the proportion of cDNA clones encoding substituted NAs.
b
Median inhibitory concentration (IC50) values are the mean of duplicate reactions.
c
NT indicates samples not tested because infectious viruses were not isolated from the corresponding specimens.