INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending February 8, 2003-Week 6

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

Florida: During week 6 (February 2-8, 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 2.4% which is slightly higher than the national baseline of 1.9%. Higher flu activity than expected for this time of year (>2%) was also reported by physicians in Indian River, Lake, Okaloosa, Palm Beach, Polk, Sarasota and Volusia counties. The influenza activity is wide spread. During the last two weeks over 50 laboratory confirmed influenza cases were reported from 15 counties across the state. Influenza A (H1N1) viruses were reported from Broward, Duval, Indian River, Leon, Lake, Madison, Monroe, Orange, Polk and St John’s counties, influenza H3N2 from Leon County, influenza A of unknown subtype from Alachua and Pinellas counties and influenza B viruses were reported from Alachua, Duval, Indian River, Leon, Pinellas and Sarasota counties. In addition, positive rapid tests were reported from Hillsborough, Orange and Pinellas counties.

National report: Four hundred fifty nine isolates (214 influenza A and 245 influenza B viruses) were made from 2,205 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week. Since September 29, 6.0% (n=2,564) of the 42,652 specimens tested nationwide have been positive. Three hundred and thirty (35%) of the 937 influenza A viruses have been subtyped; 270 were influenza A H1 viruses and 60 were influenza A (H3N2). Laboratory confirmed influenza has been reported from 49 states. The majority of influenza B isolates (51%; n=825) were identified in Texas and Missouri. Influenza A viruses were reported more frequently than influenza B viruses (range 56%-86%) in the Mountain, New England, East North Central, Pacific, and Mid-Atlantic regions. CDC has characterized 34 influenza A (H1N1), 15 influenza A (H1N2), 28 influenza A (H3N2) and 86 influenza B isolates antigenically. All strains were similar to corresponding vaccine strains. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 3.0% nationwide. The State and Territorial Epidemiologists in thirteen states (Alabama, Colorado, Indiana, Iowa, Kansas, Michigan, Missouri, New Hampshire, Pennsylvania, Rhode Island, Tennessee, Tennessee, Texas and Virginia) reported widespread influenza activity. Flu outbreaks were reported in 21 additional states. Twenty four 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 7.6% during week 6. This percentage is below the epidemic threshold of 8.3% for this time.