The number of confirmed influenza A (H1N1) cases in Japan exploded over the weekend, going from an officially reported four—all in returning vacationers—on 16 May to 129 as of 18 May. The 125 new cases are all among high-school students in Osaka and Kobe, two neighboring cities in western Japan. None of these cases has yet been linked to a returning traveler. Japanese media, citing their own surveys of local health offices, are reporting 135 confirmed cases as of late afternoon on 18 May. Despite the surge, the World Health Organization (WHO) hasn’t yet raised its pandemic alert level to indicate that a global pandemic is under way. "What we're seeing now is not the trigger for phase 6," says Peter Cordingley, spokesperson for WHO's Western Pacific Regional Office in Manila.
The spread of a novel H1N1 in North America led WHO on 29 April to raise its pandemic alert to phase 5, which indicates human-to-human spread in at least two countries in one WHO region. Phase 6, the highest level, is characterized by such community-level outbreaks in two WHO regions. Cordingley says that although the agency is aware of reports of additional cases in Japan—WHO expects the official numbers to rise—"the bulk of the cases are associated with schools, and we don't see evidence of sustained transmission in local communities."
Others think that this line has already been crossed. "Without sustained community transmission, you cannot have 100 cases," says Hitoshi Oshitani, a public health specialist at Tohoku University in Sendai.
Spain and the United Kingdom also report more than 100 cases of the new H1N1, but they accumulated more slowly than did the cases in Japan. Although the new Japan cases are concentrated among high schoolers, Oshitani says, reports are surfacing of infections among family members of the students and a bank teller, among others. He believes the outbreak’s spread will almost certainly cause Japan in the next few days to go from a designation of an early stage of community transmission to widespread community transmission in its own pandemic preparedness plan. The current, early stage goals are to hospitalize and isolate confirmed patients and trace all contacts to find the route of infection. Yet Oshitani says Kobe has already given up trying to hospitalize all its H1N1 patients, and he says it will be "probably impossible" to trace links to infection for all the patients. He predicts that in a few days Japanese health authorities will then have to acknowledge that the H1N1 virus is spreading widely through the community. The response plan would then be to confine patients at home and have authorities deliver antiviral drugs to them, something that could become a logistical challenge if the number of cases grows, Oshitani says.
He also predicts that the outbreak in western Japan will follow the course of the one among high schools in New York City, with mild cases predominating but with smaller numbers of severe cases among those with other health problems. Osaka and Kobe closed hundreds of schools to try to limit the spread of the virus.