INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending February 15, 2003-Week 7

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

Florida: During week 7 (February 9-15, 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 3.2%. 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, Brevard, Duval, Indian River, Leon, Levy, Okaloosa, Palm Beach and Polk counties. The influenza activity is wide spread. During the last three weeks over 65 laboratory confirmed influenza cases (primarily influenza A (H1N1) and influenza B) were reported from 15 counties across the state. This week influenza A H1N1 viruses were reported from Duval, Indian River and Madison counties, influenza A of unknown subtype from Duval and Pinellas counties and influenza B from Duval, Indian River and Leon counties. 

National report: Four hundred fifty one isolates (207 influenza A and 244 influenza B viruses) were made from 2,527 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week. Since September 29, 7.9% (n=3,830) of the 42,652 specimens tested nationwide have been positive. Four hundred and eighty two (33%) of the 1,442 influenza A viruses have been subtyped; 409 were influenza A H1 viruses and 73 were influenza A (H3N2). Laboratory confirmed influenza has been reported from all 50 states. The majority of influenza B isolates (52%; n=1,247) were identified in Texas and Missouri. Influenza A viruses were reported more frequently than influenza B viruses (range 56%-86%) in the Mountain, East North Central, Pacific, and Mid-Atlantic regions. Influenza B were reported more frequently in the South Atlantic, West South Central and East South Central regions. CDC has characterized 45 influenza A (H1N1), 19 influenza A (H1N2), 28 influenza A (H3N2) and 86 influenza B isolates antigenically. 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). The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 3.0% nationwide. The State and Territorial Epidemiologists in eleven states (Colorado, Indiana, Iowa, Kansas, Missouri, North Carolina, Rhode Island, Tennessee, Texas Utah, 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 7.3% during week 7. 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 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.