Pandemic (H1N1) 2009 - update 79
Weekly update (more data on virological surveillance)
18 December 2009 - The Global Influenza Surveillance Network (GISN) continues monitoring the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect humans.
Since the beginning of the pandemic in 19 April 2009 to 5 December, a total of 82 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 351,047. Of these, 258,698 (73.7%) were pandemic H1N1, 8,358 (2.4%) were seasonal A (H1), 23,777 (6.8%) were A (H3), 54,162 (15.4%) were A (not subtyped) and 6,047 (1.7%) were influenza B.
For this reporting week (15 November to 5 December 2009); a total of 21 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 11,159. Of these, 10,286 (92.2%) were pandemic (H1N1) 2009, 111 (1.0%) were seasonal A (H1), 97 (0.9%) were A (H3), 580 (5.2%) were A (not subtyped), 85 (0.8%) were influenza B.
The above numbers represent only the specimens and results reported to FluNet. Some laboratories (NICs), under pressure of the pandemic surge, do not test for seasonal subtypes and accordingly, this data should be interpreted with caution.
Detailed virological information for the European Region of WHO is included in the EuroFlu Weekly Electronic Bulletin.
Since the beginning of the pandemic in 19 April 2009 to 12th December, cumulatively 152 countries (first report from Kazakhstan and Palau was last week) shared a total of 20276 specimens (15464 clinical samples and 4812 virus isolates) with WHO CCs. Of these, 14988 specimens (clinical samples and isolates) were tested; 12019 (80.2%) were positive for influenza viruses. Of these positives, 8017(66.7 %) were pandemic H1N1, 3188 (26.5%) were seasonal influenza A, 799 (7.1%) were influenza B.
A virus mutation at position 222 of the amino acid sequence of the haemagglutinin protein of the pandemic virus has been reported. The mutation is D222G (aspartic acid to glycine), which, according to public accessible gene sequence databases and information exchange inside the Global Influenza Surveillance Network (GISN), has also been detected sporadically in viruses from around 20 countries, areas and territories. This change in the virus has been found in mild as well as severe cases. WHO, through GISN is monitoring virus mutations that are of potential public health importance.
Systematic surveillance conducted by the GISN including WHOCCs for Reference and Research on Influenza, continues to identify sporadic incidents of H1N1 pandemic viruses that show resistance to the antiviral oseltamivir. Antiviral susceptibility testing was carried out by WHO CCs and GISN labs on specimens and isolates of pandemic H1N1 viruses from at least 31 countries. 136 cases of oseltamivir resistant pandemic H1N1 have been reported by GISN so far.
According to the New England Journal of Medicine and to official media releases, a cluster of oseltamivir-resistant viruses occurred in 7 healthy people sharing one carriage in a train from Ho Chi Minh City to Hanoi in Vietnam. None of the cases knew each other before, none of them were symptomatic and none of them took oseltamivir previously or during the journey. 4 cases developed fever within 12 hours and 2 cases within 48 hours after arrival.
All of these viruses show the same H275Y mutation. All these viruses remain sensitive to zanamivir. Worldwide, more than 15,000 clinical specimens (samples and isolates) of the pandemic H1N1 virus have been tested and found to be sensitive to oseltamivir.
All pandemic H1N1 2009 influenza viruses analysed to date were antigenically and genetically closely related to the vaccine virus A/California/7/2009.