INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending May 3, 2003-Week 18

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

Florida: During week 18 (April 27 – May 3, 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 0.86%. This is lower than the national baseline of 1.9%. Higher flu activity than expected for this time of year (>2%) was reported by physicians in Indian River, Leon and Polk counties.  Light to moderate influenza activity was seen in four other counties.  

National report: During week 18, Fourteen isolates (10influenza A and 4 influenza B viruses) were made from 569 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 7.1% during Week 18.  This percentage is below the epidemic threshold of 7.7% for this time. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 0.7% nationwide. The State and Territorial Epidemiologists  in Massachusetts reported regional influenza activity. Sporatic activity was reported in 29 states, New York City and Washington, D.C.  Seventeen states reported no influenza activity.

During the past 3 weeks (weeks 16-18), 61.5% of the 13 specimens tested for influenza in the New England region were positive, and less than 50% of the specimens tested for influenza in the remaining eight influenza surveillance regions were positive.

Since September 29, 11.7% (n=10,686) of the 91,102 specimens tested nationwide have been positive.  Three thousand one hundred and eighty-eight (53%) of the 6,068 influenza A viruses have been subtyped; 2,396 (75%) were influenza A (H1)^† viruses and 792 (25%) were influenza A (H3N2) viruses.  Laboratory confirmed influenza has been reported from all 50 states.  Influenza A viruses were reported more frequently than influenza B viruses (range 57% - 86%) in the New England, East North Central, Mountain, Pacific, and Mid-Atlantic regions, and influenza B viruses were reported more frequently than influenza A viruses (range 54% - 80%) in the West North Central, West South Central, South Atlantic, and East South Central regions.  However, during the past 3 weeks (weeks 16-18), influenza A viruses were reported at least as frequently as influenza B viruses in all nine surveillance regions.  CDC has characterized 173 influenza A (H1N1), 55 influenza A (H1N2), 91 influenza A (H3N2) and 222 influenza B isolates antigenically. The neuraminidase typing for one H1 virus 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 reported in April the first fatal human case of influenza A (H7N7). 

An outbreak of highly pathogenic avian influenza A (H7N7 HPAI) in chickens began during February 2003 in the Netherlands and, despite control measures (restricting transport and culling), has spread to Belgium and Germany, to swine herds in the Netherlands, and humans.  Of the 83 confirmed cases of human H7N7 in the Netherlands, 79 exhibited conjunctivitis and 13 had mild ILI.  Possible human-to-human transmission was suggested when three family members of two poultry workers fell ill with a minor respiratory disease.  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.