INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending December 15, 2001-Week 50

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

National report: During week 50 (December 9-15, 2001), 25 of 907 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories across the United States were positive for influenza. Since September 30, a total of 13,645 specimens for influenza viruses have been tested and 231 (1.7%) were positive. Of the 231 isolates identified, 222 (96%) were influenza A viruses and 9 (4%) were influenza B viruses. One hundred and fifty-two (68%) of the influenza A viruses were subtyped, 150 were influenza A (H3N2) and 2 were influenza A (H1N1) viruses. Influenza A (H3N2) isolates were identified in Alaska Arizona, California, North Dakota, Pennsylvania, South Carolina, Texas, Utah, Wisconsin, and West Virginia; influenza A (H1N1) isolates were identified in Washington and Wisconsin; and unsubtyped influenza A isolates were identified in Alaska, California, Colorado, Hawaii, Kansas, Louisiana, Minnesota, New Jersey, New York, Oregon, Texas, Virginia, Washington, Wisconsin, and West Virginia. Influenza B isolates were identified in Hawaii, Lousiana, Michigan, Texas and Virginia. One hundred and thirty-eight (60%) of the 231 influenza viruses isolated were from the Pacific region. (Alaska, California, Hawaii, Oregon, and Washington) and 106 (46%) of the 231 viruses isolated were identified in Alaska. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) overall was 1.2%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.1% during week 50. This percentage is below the epidemic threshold of 7.7% for this time. Influenza activity was reported as widespread in Alaska and regional in Colorado and Vermont this week. Sporadic activity was reported from 36 states, New York City and Washington, DC. No influenza activity was reported from Idaho, Oklahoma, Arkansas, Mississippi, Illinois, Pennsylvania, New Jersey, Massachusetts, New Hampshire, Rhode Island and Delaware.

Florida: Influenza activity appears to be increasing in Florida with 1.42% of patients seeking care by physicians in the influenza sentinel surveillance met the case definition for ILI (> 100 F + cough and or sore throat) during week 50. This is similar to last week’s numbers while in previous weeks fewer than 1% of patients seen have had a flu-like illness. Influenza-like illness activity was detected in 11 counties from Escambia to Monroe. Higher flu activity than expected for this time of year (>2%) was reported by physicians in Escambia, Lake, Monroe, Palm Beach, and Polk counties. Influenza A (H3N3) was isolated from a patient in Polk County this week. A positive rapid antigen test was also reported from Hillsborough County. Between September 4 and December 20, influenza A (H2N3) was isolated from 10 patients residing in Broward, Collier, Duval, Hillsborough, Lee, Palm Beach Polk and St John’s Counties and influenza A of unknown subtype, was isolated from 4 patients in Pinellas and 1 patient from Hillsborough County. Influenza B was isolated in Hillsborough County. In addition, positive rapid antigen tests were reported from, Duval County (1), Hillsborough (1), Palm Beach (1), Marion (2), Miami-Dade (6) Okaloosa (2) and Volusia (6) Counties.