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H1N1 Flu Has Shorter Incubation Time, Strikes Younger Adults Print E-mail
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พฤหัสบดี, 07 พฤษภาคม 2009

        May 5, 2009 — The incubation period of the influenza A (H1N1) strain, now estimated at about 1 to 5 days, is shorter and more like seasonal influenza than originally thought, according to the World Health Organization (WHO).

The WHO continues to see a global increase in H1N1 cases. As of 8:00 am EDT, there were 1490 laboratory-confirmed cases and 30 deaths reported, with all but 1 death occurring in Mexico. The numbers represents an increase in 405 cases and 4 deaths since yesterday and are likely to be updated later today.Keiji Fukuda, MD, MPH, assistant director-general ad. interim for health security and environment at the WHO spoke today at daily media briefing."There have been a significant number of countries in Europe reporting cases," with the United Kingdom and Spain reporting the most, Dr. Fukuda said. However, he added that they are not seeing community transmission in Europe "in the same way that we are seeing community transmission in the United States or Mexico." In Europe, the cases still seem to be mostly travel related, he said.Currently, the pandemic alert level for H1N1 influenza is remaining at phase 5 and is not presently moving to the highest level of phase 6. The move to phase 6 will take place when there is community transmission in more than 1 WHO region.At the time of the media briefing, a virtual meeting of international infectious disease experts was convening to focus on clinical presentation of H1N1 influenza and was still under way. According to Dr. Fukuda, the current consensus from that meeting was that people who are infected continue to be relatively younger people, mostly younger than 60 years. "The average age seems to be people in their mid-20s," he said.The reason for the increased incidence in younger people remains unclear. According to Dr. Fukuda, it could be that younger people simply travel more and have greater exposure to the virus, or it could be that older people have developed a greater resistance than younger people. "With influenza, oftentimes we see the infections go to younger people first and then go to older people later," he said.According to Dr. Fukuda, men and women are being infected at the same rate, which is similar to seasonal influenza. Severe respiratory illness, such as severe pneumonia requiring ventilation, seems to be the cause for most hospitalizations and deaths. "But the big question is...does this occur relatively infrequently or does this occur frequently," he said."In general we have seen a number of healthcare workers infected, but it's not certain that they got infected in the healthcare setting," Dr. Fukuda said. "And it has not been transmitted to a lot of healthcare workers."

The viral specimens in various regions continue to look very similar. The WHO maintains that the H1N1 influenza is susceptible to oseltamivir and zanamivir, the neuraminidase inhibitors, but the virus shows resistance to the class of agents that includes rimantadine and amantadine, he said.

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