Pandemic influenza A (H1N1) situation report of Japan, update 22
November 27, 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 46th epidemiologic week (November 9-15 2009) (Figure 1). The number of cases reported per sentinel* in Japan was 35.15, which has increased compared to previous week (32.76/sentinel). Based on this number, newly diagnosed ILI patients during this week are estimated to be approximately 1.64 million nationwide.

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

Aichi Prefecture reported the highest cases per sentinel (58.75), followed by Oita Prefecture (53.64) and Ishikawa Prefecture (49.77). Aichi has 31 community health centers (HCs) of which 23 health center (71%) were above the alert level (30.00). Oita has 7 HCs of all HCs (100%) were above the alert level. Ishikawa has 5 HCs of which 4 HCs (80%) were above alert level. For the details, refer to the Map of ILI epidemic level at following URL (Japanese only):

According to the school-based ILI absenteesm report from Ministry of Health Labor and Welfare (MoH), in week 46 (Figure 2), 879 schools in Japan, have been closed due to the ILI outbreak within the schools. In addition, one whole grade was suspended in 3,975 schools and a class was closed in 12,356 schools with multiple infected students..



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


There were 724 reported hospitalization cases due to pandemic influenza AH1 pdm infection during November 11 to 17, according to MoH. According to the stratified by age group, 5- 9 year old was 338 cases (47%) which was the highest number of the hospitalization. The second highest one was under 5 year old which was 143 cases (20%). Third one was from 10-14 year old which was 106 cases (15%). Acute encephalitis was 22 cases (3%) and mechanical ventilator used case was 24 (3%) among all inpatients.

As of 17 November 2009, cumulative number of the inpatient cases was 7,708 (Cumulative number of the inpatient case included case who has already hospitalized on November 28 or newly inpatient case on July 29 or later.). Among the inpatient case, 2,755 cases have some kind(s) of underlying disease. Of those inpatient cases, 1,865 cases (68%) have had chronic respiratory illness was the highest underlying disease. At the same time, cumulative number of the death case was 65 persons of which 55 cases were inpatient and other 10 cases were outpatient cases at the same time.

According to Infectious Agents Surveillance Report, most of the influenza viruses detected/isolated from specimens collected influenza cases during the week 19 through 46 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.