The national reporting period for influenza begins in early fall and continues through late May. Preliminary data from national influenza surveillance systems indicate that the 2004-2005 season was of moderate severity.
On a global scale, 2004-2005 saw the reemergence of the highly pathogenic avian influenza, subtype H5N1, in parts of Southeast Asia, which, as of August 2005, has resulted in 112 cases and 57 deaths since January 2004. With the possible exception of one case in Thailand, all cases have been due to contact with sick or dead poultry. These developments in Asia are of particular concern due to the rapid ability of the influenza virus to undergo genetic reassortment, and it is speculated that if efficient human-to-human transmission of avian influenza occurs, it could result in a global pandemic characterized by a high fatality rate.
The first isolate of the 2004-2005 influenza season in Texas was identified as influenza A H3 by the Texas Department of State Health Services Virology Lab on 10/9/04. The specimen was collected from a 2 year-old residing in New Braunfels (Comal County).
In Texas, influenza activity peaked in February, which mirrored that of the nation. The flu activity level declined to “sporadic” for the week ending 4/2/05, and then dropped to "no activity" for the week ending 4/30/05 where it remained for the duration of the season. During the week ending 2/5/05, a new strain of H3N2 that did not match the current vaccine was identified in California. This strain was genetically similar to A/Fujiian yet different enough that the vaccine did not provide optimal protection. The first CDC confirmation that this new strain was circulating in Texas was received during the week of 2/26/05 (specimen was collected on 12/29/04) and was identified in an individual from North Texas who had not been vaccinated.
The flu vaccine composition for 2004-2005 included: A/Fujiian H3N2, A/New Caledonia H1N1, and B/Shanghai. Overall, the majority of influenza strains circulating in the U.S. were well matched to the season’s vaccine, with one notable exception. The primary circulating strain of the season was A/California H3N2. The vaccine strain, A/Fujiian H3N2, did not provide optimal protection from this strain. However, the vaccine offered more protection than no vaccination at all.
Over the course of the 2004-2005 influenza season, the DSHS virology lab received 1,422 respiratory specimens. Of those, 43% were positive for influenza, and 33% were identified as A H3. An additional 2% were identified as Influenza A but could not be subtyped. 8% were identified as influenza B. Like other state virology laboratories in the country, DSHS periodically submits early, mid, and late-season, as well as unusual isolates, to the CDC for strain characterization. Of the 57 isolates submitted: 3 were identified as A/Wyoming/03/2003-like (H3N2), 3 were identified as A/Korea/770/2002-like (H3N2) , 25 were identified as A/California/07/2004-like (H3N2) , 9 were identified as B/Shanghai/361/2002-like, and 1 was identified as B/Hong Kong/1434/2002-like . The rest of the specimens were either unable to be identified or still pending (do not know the break-down at this time).