From May 2009, PHIs have carried out rapid detection of pandemic influenza AH1pdm virus by RT-PCR to differenciate from seasonal influenza virus. In week 19 (May 4-10), the first two influenza AH1pdm virus were isolated. The number of reports of detection/isolation of AH1pdm sharply increased from week 20 (May11-17), exceeded 500 in week 28 and decreased from week 4 of 2010 and kept a low level after week 12 of 2010 (Fig. 1). |
From week 19 of 2009 to week 19 of 2010, PHIs in all 47 prefectures (including Tokyo Metropolis) reported isolation/detection of AH1pdm from 31,435 cases. During the same period, isolation/detection of seasonal AH1 from 66 cases, AH3 from 948 cases and B from 203 cases were reported . The proportion of AH1pdm to all influenza virus is 96%.
During 17 weeks from week 19 to week 35 of 2009 (the last week of the 2008/09 season), isolation/detection of AH1pdm from 9,724 cases in all prefectures, AH1 from 66 cases in 24 prefectures, AH3 from 913 cases in 40 prefectures, and B from 103 cases in 21 prefectures were reported (Fig. 2, lower).
From week 36 of 2009 (the first week of the 2009/10 season) to week 19 of 2010, isolation/detection of AH1pdm from 21,710 cases in all prefectures were reported. In addition, isolation/detection of seasonal AH3 (from 15 cases in 10 prefectures during weeks 36-44 and 20 cases in 10 prefectures during weeks 8-19), B/Yamagata lineage (from a case in Osaka Prefecture in week 47, a case in Shiga Prefecture in week 2, 4 cases in 2 prefectures in weeks 9-10, 3 cases in 2 prefectures in weeks 13-14 and 2 cases in Mie Prefecture in week 17), B/Victoria lineage (from a case in Niigata Prefecture in week 50 and 78 cases in 14 prefectures during weeks 3-17) and B/lineage not determined (from 10 cases in 5 prefectures during weeks 5-16) were reported. However, seasonal AH1 has not been reported since week 36 (Fig. 2, upper).