INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending February 22, 2003-Week 8

Carina Blackmore, M.S. Vet. Med., Ph.D.

Florida: During week 8 (February 16-22, 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 3.0%. This is the highest influenza activity reported so far this season and also higher than the national baseline of 1.9%. Higher flu activity than expected for this time of year (>2%) was reported by physicians in Alachua, Broward, Indian River, Monroe, Orange, Polk and Sarasota counties. The influenza activity is wide spread. During the last three weeks over 66 laboratory confirmed influenza cases (primarily influenza A (H1N1) and influenza B) were reported from 11 counties across the state. This week influenza A H1N1 viruses were reported from Duval, Indian River, Madison and Polk counties and influenza B from Duval, Indian River, Leon, Levy and Seminole counties. 

National report: Three hundred sixty one isolates (215 influenza A and 154 influenza B viruses) were made from 2,119 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week. Since September 29, 9.1% (n=4,875) of the 53,480 specimens tested nationwide have been positive. Seven hundred and seventy eight (39%) of the 2,020 influenza A viruses have been subtyped; 622 were influenza A H1 viruses and 156 were influenza A (H3N2). Laboratory confirmed influenza has been reported from all 50 states. The majority of influenza B isolates (46%; n=2,855) were identified in Texas and Missouri. Influenza A viruses were reported more frequently than influenza B viruses (range 62%-89%) in the Mountain, East North Central, Pacific, and Mid-Atlantic regions. Influenza B were reported more frequently in the South Atlantic, West South Central, West North Central and East South Central regions. CDC has characterized 45 influenza A (H1N1), 20 influenza A (H1N2), 34 influenza A (H3N2) and 86 influenza B isolates antigenically. All influenza A H1 strains were similar to corresponding vaccine strains. Seven of the 34 (21%) characterized H3N2 strains showed reduced titers to antiserum produced against the H2N2 vaccine strain (A/Panama/2007/99). One influenza B strain was more similar to B/Shizuoka/15/01 than to the B vaccine strain (B/Hong Kong/ 330/01). The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 2.8% nationwide. The State and Territorial Epidemiologists in thirteen states (Colorado, Indiana, Iowa, Minnesota, North Carolina, Oregon, Rhode Island, Tennessee, Texas Utah, Vermont, Virginia and Wisconsin) reported widespread influenza activity. Flu outbreaks were reported in 23 additional states. Thirteen states reported sporadic influenza activity. The proportion of deaths attributed to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.4% during week 8. This percentage is below the epidemic threshold of 8.3% for this time. 

An avian flu virus strain, influenza A H5N1, has been recovered from two recent influenza cases in Hong Kong. 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.