TABLE 1.
Subtype-specific frequency of amantadine-resistant H1N1 and H3N2 strains from posttreatment samples during the 1999-2000 and 2000-2001 influenza seasons in Niigata City, Japan
| Season | H1N1 strains
|
H3N2 strains
|
Total by season (%) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| No. of strains with amino acid substitution at:a
|
No. of total resistant strains/isolates (%) | No. of strains with amino acid substitution ata:
|
No. of total resistant strains/isolates (%) | ||||||||
| 26 | 27 | 30 | 31 | 26 | 27 | 30 | 31 | ||||
| 1999-2000 | 0 | 4 | 0 | 1 | 5/22 (22.7) | 0 | 1 | 3 | 15 | 19/59 (32.7) | 24/81 (29.6) |
| 2000-2001 | 1 | 2 | 0 | 1 | 4/23 (17.4) | 0 | 0 | 1 | 2 | 3/7 (42.9) | 7/30 (23.3) |
| Total by subtype (%) | 1 | 6b | 0 | 2c | 9/45 (20.0) | 0 | 1b,d | 4d | 17c,d | 22/66 (33.3) | 31/111 (27.9) |
Each number indicates the number of cases of amantadine-resistant influenza virus A strains with the respective amino acid substitutions in the transmembrane domain of the M2 protein.
The proprtion of amino acid substitutions at position 27 was significantly higher in H1N1 strains than in H3N2 strains (Yates corrected χ2 test, P < 0.01).
The proportion of amino acid substitutions at position 31 was significantly higher in H3N2 strains than in H1N1 strains (Yates corrected χ2 test, P < 0.05).
The proportion of amino acid substitutions at position 31 was significantly higher than at positions 27 and 30 within H3N2 strains (Yates corrected χ2 test, P < 0.001, respectively).