INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending May 17, 2003-Week 20

Melissa Covey, Department of Health, Bureau of Laboratories reports that the following activities occurred: 

Florida: During week 20 (May 11-17, 2003)* influenza activity, calculated based on the proportion of patients with influenza-like illness (ILI) seeking care by physicians participating in the Florida Sentinel Physicians Surveillance Network was 0.73%. This is lower than the national baseline of 1.9%. Higher flu activity than expected for this time of year (>2%) was reported by surveillants in Indian River and Polk counties.  Light to moderate influenza activity was seen in five other counties.

National report: During week 20, four isolates (3 influenza A and 1 influenza B viruses) were made from 511 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week.   The proportion of deaths attributed to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.3% during Week 20.  This percentage is below the epidemic threshold of 7.5% for this time. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 0.9% nationwide. The State and Territorial Epidemiologists  in Massachusetts reported regional influenza activity. Twenty-one states, New York City and Washington D.C. reported sporadic activity, and 24 states reported no influenza activity.

  Since September 29, 11.6% (n=11,027) of the 94,966 specimens tested nationwide have been positive.  Three thousand three hundred and eighty-one (53%) of the 6,324 influenza A viruses have been subtyped; 2,534 (75%) were influenza A (H1N1 and H1N2) viruses and 847 (25%) were influenza A (H3N2) viruses.  Influenza A viruses were reported more frequently than influenza B viruses (range 58% - 86%) in the New England, East North Central, Pacific, Mountain, and Mid-Atlantic regions, and influenza B viruses were reported more frequently than influenza A viruses (range 53% - 78%) in the West North Central, West South Central, South Atlantic, and East South Central regions. 

  CDC has characterized 173 influenza A (H1N1), 55 influenza A (H1N2), 105 influenza A (H3N2) and 254 influenza B isolates antigenically. The neuraminidase typing for one H1 viruses is pending.  All influenza A strains were similar to corresponding vaccine strains. One influenza B strain was more similar to B/Shizuoka/15/01 than to the vaccine strain (B/Hong Kong/ 330/01). 

  International report:

The Netherlands:  No further updates have been found for the outbreak of highly pathogenic avian influenza A (H7N7 HPAI) in chickens which began during February 2003 in the Netherlands.  Between February and April of 2003, this outbreak had spread to Belgium and Germany, to swine herds in the Netherlands, and to humans.  The 83 confirmed cases of human H7N7 in the Netherlands included one death, 79 with conjunctivitis and 13 with mild ILI.  The WHO Influenza Collaborating Centers are to begin production of a reagent kit to identify H7N7 viruses.  More information about this outbreak of H7N7 HPAI can be found at:  http://www.who.int/csr/don/2003_04_24/en/

  Asia:  An avian flu virus strain, influenza A (H5N1), was recovered from two influenza cases in Hong Kong earlier this year. CDC has issued recommendations on increased influenza surveillance in the United States.  Of particular importance is to consider influenza cultures on patients, with recent travel histories to Asia, who are hospitalized with unexplained pneumonia, acute respiratory distress syndrome or severe respiratory illness. 

 * Reporting is incomplete for this week. Numbers may change as more reports are received.