Pandemic influenza A (H1N1) situation report of Japan, update 21
November 6, 2009
According to the National Epidemiological Surveillance for Infectious Diseases
in Japan, the numbers of reported cases of the Influenza like Illness (ILI)
increased in the Epidemiological Week 42 (October 12-18, 2009) (Figure
1). The number of cases reported per sentinel* was 17.65, increased from
12.92 in previous week. Newly diagnosed ILI patients during this week are
estimated to be approximately 0.83 million nationwide based on this number.
Figure 1. Influenza (like illness) cases reported weekly per sentinel
Hokkaido reported the highest cases per sentinel (57.93), followed by Aichi
Prefecture (31.78) and Fukuoka Prefecture (29.08). Hokkaido has 30 community
health centers (HCs) of which 23 health centers (77%) were above the alert
level (30.00) and 4 HCs (13%) were above warning threshold (10.00). For
the details, refer to the Map of ILI epidemic level at following URL (Japanese only):
According to the ILI report from Ministry of Health Labor and Welfare (MoH),
in week 42 (Figure 2), 619 schools in Japan, have been closed due to the
ILI outbreak within the schools. In addition, one whole grade was suspended
in 2,051 schools and a class was closed in 5,864 schools with multiple
Figure 2. The number of closed class, grade or school and ILI surveillance
There were 445 reported
hospitalization cases due to pandemic influenza A (H1N1) infection during October
14 to 20, according to MoH.
According to the Infectious Agents Surveillance
Report, over 99% of the influenza viruses detected/isolated from specimens
collected from influenza cases during weeks 19 to 43 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.