INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending February 1, 2003 - Week 5

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

Florida: During week 5 (January 25-February 1, 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 2.5% 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 Duval, Indian River, Lake, Leon, Monroe, Okaloosa, Orange, Polk and Sarasota counties. Influenza A (H1N1) viruses were reported from Duval, Lake and St John’s counties, influenza H3N2 from Leon County and influenza B viruses were reported from Duval, Indian River, Orange and St John’s counties this week. Positive rapid tests were reported from Orange and Pinellas counties. During the last 4 weeks influenza A (H1N1) has also been reported from Broward, Leon, Okaloosa, Orange, Palm Beach and Volusia counties, influenza A of unknown subtype from Alachua and Pinellas counties and influenza B from Hillsborough, Okaloosa, Pinellas, Santa Rosa and Sarasota counties. 

National report: One hundred sixty-six isolates (49 influenza A and 117 influenza B viruses) were made from 1,157 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week. Since September 29, 4.7% (n=1,714) of the 36,753 specimens tested nationwide have been positive. Two hundred and thirty-seven (44%) of the 543 influenza A viruses have been subtyped; 192 were influenza A H1 viruses and 45 were influenza A (H3N2). Laboratory confirmed influenza has been reported from 47 states. The majority of influenza B isolates (70%; n=820) were identified in Texas and Missouri. Influenza A viruses were reported more frequently than influenza B viruses (range 63%-85%) in the Mountain, New England, East North Central, Pacific, and Mid-Atlantic regions. CDC has characterized 34 influenza A (H1N1), 15 influenza A (H1N2), 23 influenza A (H3N2) and 47 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 2.5% nationwide. The State and Territorial Epidemiologists in six states (Alabama, Colorado, Missouri, Tennessee, Texas and Virginia) reported widespread influenza activity. Flu outbreaks were reported in 18 additional states (Arkansas, Delaware, Florida, Georgia, Iowa, Kansas, Louisiana, Minnesota, Mississippi, Nebraska, New Mexico, New York, Oklahoma, Pennsylvania, Rhode Island, South Dakota, Washington and Utah). Sporadic influenza activity was reported from 24 states. The proportion of deaths attributed to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.2% during week 5. This percentage is below the epidemic threshold of 8.2% for this time.