Pandemic influenza A (H1N1) situation report of Japan, update 23
December 4, 2009


According to the National Epidemiological Surveillance for Infectious Diseases in Japan, the numbers of reported cases of the Influenza like Illness (ILI) have been increasing in the 47th epidemiologic week (November 16-22, 2009) (Figure 1). The number of cases reported per sentinel* in Japan was 38.89, which has increased compared to previous week (35.15/sentinel). Based on this number, newly diagnosed ILI patients during this week are estimated to be approximately 1.73 million nationwide.

Figure 1.  Influenza (like illness) cases reported weekly per sentinel

Oita Prefecture reported the highest cases per sentinel (77.21), followed by Fukui Prefecture (71.25) and Ishikawa Prefecture (65.02). Influenza activity of all 7 community health centers (HCs) in Oita Prefecture (100%) were above the alert level (30.00). Fukui Prefecture has 6 HCs of 5 HCs (83%) were above the alert level. Ishikawa Prefecture has 5 HCs of which all HCs (100%) were above alert level. For the details, refer to the Map of ILI epidemic level at following URL (Japanese only):

Activity in Hokkaido has been decreasing with the peak in 43th week (61.43/sentinel). Akita Prefecture has been continuously decreasing in the most recent three-week. Tokyo Metropolitan, Osaka Prefecture and Hyogo Prefecture have also been on a decreasing trend in the most recent three-week.



Figure 2. The number of closed class, grade or school and ILI surveillance by week


There were 856 reported hospitalization cases due to pandemic influenza AH1 pdm infection during November 18 to 24, according to MoH. By age group, the largest report (401 cases; 47% of all age) remained in the 5-9 year-olds, followed by the 1-4 year-olds (194; 23%) and the 10-14 year-olds (116; 14%). Acute encephalitis was diagnosed in 23 cases (3%) and mechanical ventilator was used in 35 (4%) among all hospitalized cases.

As of 24 November 2009, cumulative number of the hospitalized cases was 9,181 (Cumulative number of the hospitalizedt case included case who has already hospitalized on July 28 and new hospitalized case on July 29 or later.). Among the hospitalized case, 3,246 cases have some kind(s) of underlying disease, in which 2,194 cases (68%) have had chronic respiratory illness. Cumulative number of the death was 73.

According to Infectious Agents Surveillance Report, most of the influenza viruses detected/isolated from specimens collected influenza cases during the week 19 through 47 were AH1pdm (Figure 3).

Figure 3. Weekly reports of influenza virus isolation/detection

* The number of sentinel clinics and hospitals is decided from the calculation based on relative population of the jurisdiction of each public health center and the adjustments with consideration enabling comprehend the incidents in the whole area of the prefecture. The sentinel points for influenza like illness consist from approximately 3,000 pediatric hospitals/clinics and 1,800 internal medicine hospitals/clinics around the country.