INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending April 19, 2003-Week 16

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

Florida: During week 16 (April 13-19, 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 1.003%. 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, Palm Beach and Polk counties.  Light to moderate influenza activity was seen in seven other counties. 

National report:* During week 16, twelve isolates (7 influenza A and 5 influenza B viruses) were made from 600 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 7.6% during week 16.  This percentage is below the epidemic threshold of 7.9% for this time. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 1% nationwide. The State and Territorial Epidemiologists in Alaska reported widespread influenza activity. Four states (Idaho, Montana, North Dakota, and Ohio) reported regional activity, and 32 states and New York City reported sporatic influenza activity. Nine states reported no influenza activity.  During the past 3 weeks (weeks 14-16), 22.7% of the specimens tested for influenza in the New England region were positive, between 6.2% and 10.3% of the specimens tested for influenza in the Pacific, Mountain, West North Central, and East North Central regions were positive, and less than 3.0% of the specimens tested for influenza in the East South Central, West South Central, Mid-Atlantic, and South Atlantic regions were positive.  However, during the past 3 weeks (weeks 14-16), influenza A viruses were reported more frequently than influenza B viruses in all nine surveillance regions. 

Since September 29, 11.5% (n=10,148) of the 88,142 specimens tested nationwide have been positive.  Two thousand eight hundred and seventeen (50%) of the 5,647 influenza A viruses have been subtyped; 2,196 (78%) were influenza A (H1) viruses and 621 (22%) 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% - 87%) 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 58% - 80%) in the South Atlantic, West North Central, West South Central, and East South Central regions. However, during the past 3 weeks (weeks 14-16), influenza A viruses were reported more frequently than influenza B viruses in all nine surveillance regions.  CDC has characterized 140 influenza A (H1N1), 46 influenza A (H1N2), 82 influenza A (H3N2) and 222 influenza B isolates antigenically. The neuraminidase typing for 42 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:

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.