# 4184
From PLoS Currents: Influenza, a new study on the low CFR (Case Fatality Ratio) and epidemiological characteristics of the novel H1N1 virus in Japan.
Epidemiological characteristics and low case fatality rate of pandemic (H1N1) 2009 in Japan
By Taro Kamigaki and Hitoshi Oshitani
Pandemic (H1N1) 2009 has been causing large outbreaks in Japan. Yet, the case fatality rate (CFR) remains low and only 85 deaths have been confirmed as of December 17, 2009. Surveillance data was analyzed to define epidemiological characteristics of pandemic (H1N1) 2009 in Japan.
It was shown that most of the reported influenza-like illness cases and hospitalizations have occurred in those aged 5–9 years and 10–14 years, in whom CFR is extremely low.
However, CFRs are higher in small children (<5 years) and adults. The transmission to these age groups may possibly have been minimized through aggressive suspension of classes in schools.
While this entire article is worth reviewing, some of the demographics of who was infected, and hospitalized, by this virus are particularly fascinating.
They show, about as dramatically as any analysis that I’ve seen, just how much of the influenza burden has been borne by children, teenagers, and young adults.
A brief excerpt:
Age Distribution of Cases, Hospitalized Cases, and Deaths in Japan
In Japan, there are about 3000 pediatric and 2000 adult outpatient clinics participating in the influenza sentinel surveillance system that report weekly the number of influenza-like illness (ILI) stratified by age group. Between weeks 28 and 48 of 2009, 1,272,725 ILI cases were reported through the sentinel surveillance system, and it is estimated that 12.6 million people with ILI had visited outpatient clinics [7]. During this period, more than 99% of influenza viruses isolated in Japan were pandemic H1N1. Therefore, it can be assumed that majority of ILI cases during this period were caused by pandemic H1N1.
Figure 1. (a) Reported cases of influenza-like illness and rate per 100,000 between week 28 and week 48, 2009 in Japan (Upper). (b) Number of hospitalized cases and hospitalization rate per 100,000 (as of 2 December) (Lower)
