MANILA, 20 May 2009, 1600 hrs—On May 20, Japan reported that it had 209 laboratory-confirmed cases of influenza A(H1N1), an increase of 33 cases from the previous day. Most of the cases are related to high schools at Hyogo Prefecture where 132 infections have been confirmed, and at Osaka which has a confirmed case count of 73. No deaths have been reported in the Western Pacific Region.
There are now 231 laboratory-confirmed cases of influenza A(H1N1) in the Western Pacific Region:
- 1 in Australia
- 4 in China
- 3 in Hong Kong (China)
- 209 in Japan
- 2 in Malaysia
- 9 in New Zealand
- 3 in the Republic of Korea
Japan's confirmed cases of influenza A(H1N1) comprise the cases at Hyogo Prefecture, Osaka and the first four cases announced earlier in May. The new cases seem to be mainly associated with schools and, at this stage, there is no clear sign of the virus transmitting into local communities. However, there are a small number of cases in Hyogo Prefecture where public health authorities are finding it difficult to make a clear link to an affected school. Further information on those cases is expected in the near future as investigations continue.
Japan considers this to be a school-related outbreak. But national authorities have warned all prefectures in Japan that the virus could spread to other regions and has asked local public health authorities to be vigilant. WHO is collaborating closely with Japan's public health authorities to monitor this evolving situation. The government of Japan is providing regular updates throughout each day on the situation both to WHO and to the public
New report on clinical features of influenza A(H1N1)
New evidence is emerging to support indications that influenza A(H1N1) differs somewhat from seasonal influenza. Although more information about influenza A(H1N1) is required and the number of cases studied to date remains relatively small, the evolving picture strongly suggests that governments should continue to prepare for a pandemic and not assume that outbreaks of influenza A(H1N1) will resemble seasonal influenza.
Though this outbreak has been described as a 'mild' pandemic, recent data from 553 confirmed cases in California released on 18 May in the Morbidity and Mortality Weekly Report show that:
- 5.4% confirmed cases of influenza A(H1N1) in California had to be admitted to hospital for in-patient treatment
- The median age of those requiring in-patient hospital care was 27 years
- Around one-third of hospitalized patients were reported to have been previously healthy with no underlying medical conditions
- Approximately one in five people admitted to hospital needed intensive care
The number of patients suffering from influenza A(H1N1) who required more than one day in hospital was higher than would have been expected with seasonal flu. The comparatively young age of those hospitalized was also unusual, as seasonal flu tends to disproportionately affect the elderly. Additionally, a number of the hospitalized patients in California were young adults with no underlying medical conditions, which again is not normally the case with seasonal flu.
The case for continued vigilance is further reinforced by an analysis of early data from Mexico published on 12 May in the journal Science and facilitated by the WHO Rapid Pandemic Assessment Collaboration. It pointed out that early fatality rates from influenza A(H1N1) in Mexico were similar to those seen during the 1957 influenza pandemic and estimated that up to three times as many people may have been infected with influenza A(H1N1) than would have been expected if the outbreak had been caused by seasonal influenza.
These variations are not surprising as influenza A(H1N1) is a newly identified virus to which populations are likely to have little or no immunity. It is reassuring that the majority of people infected with this virus suffer a self-limiting illness. However, this early data shows a higher than expected need for hospital care particularly in young adults, and when coupled with the many unknowns about the virus means governments should continue to be vigilant and prepare for outbreaks and a possible global pandemic.
Global case count
As of 06:00 GMT, 20 May 2009, 40 countries have officially reported 9 855 cases of influenza A(H1N1) infection, with 79 deaths. Mexico has reported 3 648 laboratory-confirmed human cases of infection, including 72 deaths. The United States of America has reported 5 123 laboratory-confirmed human cases, including five deaths. Canada has reported 496 laboratory confirmed human cases, including one death. Costa Rica has reported nine laboratory-confirmed human cases, including one death.
The following countries have reported laboratory confirmed cases with no deaths: Argentina (1), Australia (1), Austria (1), Belgium (5), Brazil (8), Chile (4), China (4), Hong Kong (China) (3), Colombia (12), Cuba (3), Denmark (1), Ecuador (1), El Salvador (6), Finland (2), France (15), Germany (14), Greece (1), Guatemala (3), India (1), Ireland (1), Israel (7), Italy (9), Japan (209), Malaysia (2), Netherlands (3), New Zealand (9), Norway (2), Panama (59), Peru (2), Poland (2), Portugal (1), Republic of Korea (3), Spain (107), Sweden (3), Switzerland (1), Thailand (2), Turkey (2), and the United Kingdom (102).
WHO is not recommending travel restrictions related to the outbreak of the influenza A(H1N1) virus. Individuals who are ill should delay travel plans and returning travellers who fall ill should seek appropriate medical care. These recommendations are prudent measures which can limit the spread of many communicable diseases, including influenza.
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