2005-2006 Texas Influenza Surveillance Activity

Update on Avian Influenza A (H5N1)

On a global scale, 2005-2006 saw the continued spread (in poultry and wild birds) of the highly pathogenic avian influenza, subtype H5N1, in many previously unaffected African, Asian, and European countries. For a complete list of countries, refer to the World Organization for Animal Health website.

To date, 241 laboratory confirmed human cases of H5N1 with 141 deaths (59% mortality rate) have been detected in 10 countries across Asia and Africa. The majority of cases have been reported in Vietnam (93); however, the largest number of deaths have been reported in Indonesia (46 deaths-77% mortality rate).

Only very limited human-to-human transmission has been documented. In June 2006, WHO (World Health Organization) investigated a cluster of H5N1 cases in a family in Indonesia. Seven of the eight family members who became ill tested positive for the virus. Only the index case had any contact with infected poultry, and it is believed that transmission to 6 of the other family members was a result of close contact to the index case. One of the cases is thought to have become ill after caring for his son, who was infected by the index case. Transmission outside of the extended family was not documented. Due to the multiple recent outbreaks in Indonesia, enhanced surveillance for cases of H5N1 continues in certain regions.

Seasonal Influenza in the U.S.

The national reporting period for influenza begins in early fall and continues through late May. According to the Centers for Disease Control and Prevention (CDC), flu activity for the nation was less intense in the 2005-2006 season than in recent seasons; however, the season lasted longer, with the peak occurring in March rather than the more typical peak in February. Influenza A H3N2 was the predominant subtype isolated with a low level of A H1N1 and the late season occurrence of influenza B.

The flu vaccine composition for 2005-2006 included: A/California/7/2004-like (H3N2), A/New Caledonia/20/99 (H1N1), and B/Shanghai/361/2002-like. Since October 1, 2005, CDC has characterized 1,019 influenza viruses submitted by U.S. laboratories. The H1N1 component of the vaccine appears to have been a good match to circulating strains with 97% of the viral isolates characterized as being antigenically similar to A/New Caledonia/20/99 (H1N1). The H3N2 component of the vaccine was less well matched with 72.8% being antigenically similar to A/California/7/2004-like (H3N2). The influenza B component of the vaccine was the least well matched of all the components with only 18.7% of the viral isolates even belonging to the same lineage as B/Shanghai/361/2002-like. The majority of influenza B viruses isolated (81.3%) belonged to the B/Victoria lineage, with virtually all being similar to B/Ohio/1/2005, and this is the strain that has been selected as the B component of the 2006-2007 vaccine. The 2006-2007 influenza vaccine will include the following components:

• An A/New Caledonia/20/99-like (H1N1) virus;
• An A/Wisconsin/67/2005-like (H3N2) virus (represented by A/Wisconsin/67/2005 and Hiroshima/52/2005 strains);
• A B/Malaysia/2506/2004-like virus (represented by B/Malaysia/2506/2004 and B/Ohio/1/2005 strains)

On January 14, 2006, the CDC released an interim recommendation against the use of amantadine and rimantadine for the treatment or prophylaxis of influenza A in the United States during the 2005-2006 season. A significant increase in drug resistance in the currently circulating strains of the virus has been observed over the past 3 years. Zanamivir or oseltamivir are currently recommended for antiviral treatment or prophylaxis when warranted.

Seasonal Influenza in Texas

Over the course of the 2005-2006 influenza season, the Texas Department of State Health Services (DSHS) laboratory received 872 respiratory specimens and, of those, 382 (44%) were positive for influenza. Of those positives, 304 (80%) were identified as A H3; 5 (1%) were identified as A H1; 15 (4%) were identified as A--unable to be subtyped due to lack of hemagglutination titer, and 58 (15%) were identified as B.

Respiratory specimen submission increased substantially beginning the week of December 18, 2005 and peaked the week of January 22, 2006. Specimen submission sharply declined the week of February 5, 2006. Travis, Bexar, and Dallas Counties submitted the greatest number of specimens.

The majority of specimens submitted (50%) were from individuals between the ages of 5-24. This is not unexpected given that infection rates for influenza are highest in children and young adults.

Like other state virology laboratories in the country, DSHS submits early, mid, and late-season as well as unusual isolates to the CDC for strain characterization. Ninety-seven isolates were submitted during the 2005-2006 season to CDC. The following strains were identified:

The first isolate of the 2005-2006 influenza season in Texas was collected October 11, 2005 (MMWR week 41) and identified as influenza A by Scott and White laboratory in Temple, Texas. The specimen was collected from a 76 year-old resident of Waco, Texas (McLennan County) and later identified by CDC as influenza A/California/07/2004-like (H3N2). This strain predominated early in the season with A/New York/55/2004-like (H3N2) appearing in December 2005. Very limited transmission of A/Wisconsin/67/2005-like (H3N2) also occurred during this time. A/New Caledonia/20/99-like (H1N1) was not isolated until very late in the season (March) and only very infrequently thereafter.

Influenza B was first isolated in Texas at the beginning of January with the almost simultaneous appearance of B/Florida/07/2004-like and B/Ohio/01/2005-like in residents of Dallas County. Interestingly, the strains represented two distinct lineages of the B virus (B/Yamagata and B/Victoria respectively). As was the case in other parts of the U.S., influenza B appeared late in the season in Texas with B/Ohio/01/2005-like accounting for 67% of the influenza B strains submitted and characterized by CDC and B/Florida/07/2004-like accounting for the remaining 33%.

According to data from the Texas Sentinel Provider Surveillance Network (SPSN), influenza-like illness (ILI) peaked the last week of December 2005. During this week, SPSN providers reported that influenza-like illness accounted for 8.3% of all physician visits. This is earlier than a more typical season, with the peak normally occurring in February. The flu activity level declined to "no activity" beginning week 19 (week ending May 13, 2006) where it remained for the duration of the season. The previous 2004-2005 season declined to “no activity” beginning week 17 (week ending April 30, 2005).

For more information on how to become a sentinel provider, please visit the following website: http://www.dshs.state.tx.us/idcu/disease/influenza/surveillance/iliNet/

For questions concerning this report or influenza surveillance in general in Texas, please contact Stacy Davlin at: (512) 458-7676.

2005 - 2006 Texas Influenza Surveillance Information --- Flu Reports

For the week ending: 
10/15/05; 10/22/05; 10/29/05; 11/05/05; 11/12/05; 11/19/05; 11/26/05; 12/10/05; 
12/17/05; 12/24/05; 01/07/06; 01/14/06; 01/21/06; 01/28/06; 02/04/06; 02/11/06; 
02/18/06; 02/25/06; 03/04/06; 03/11/06; 03/18/06; 03/26/06; 04/01/06; 04/08/06; 
04/15/06; 04/22/06; 04/29/06; 05/12/06; 05/19/06; 05/20/06