INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending October 20, 2001-Week 42

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

National report: During week 42 (October 14-20, 2001), none of the 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 1,936 specimens for influenza viruses have been tested and 11 (1%) were positive. Of the 11 isolates identified, 4 were influenza A (H3N2) viruses, 6 were unsubtyped influenza A viruses, and 1 was an influenza B virus. Influenza A isolates have been identified in Alaska, Arizona, New York, and Texas. The influenza B isolate was identified in Texas.  The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) overall was 1.5%, 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 6.4% during week 42. This percentage is below the epidemic threshold of 6.9% for this time. Thirteen state and territorial health departments (Alaska, Florida, Indiana, Kansas, Kentucky, Minnesota, Missouri, New Mexico, New York, Ohio, Pennsylvania, West Virginia, and Wyoming) reported sporadic influenza activity and 36 reported no influenza activity.

Florida: Data from Florida suggests low levels of influenza activity. Overall, one percent 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 42. Influenza-like illness activity was detected in 11 counties from Duval to Miami Dade. Higher flu activity than expected for this time of year (>2%) was reported by physicians in Broward, Palm Beach and Sarasota County. Between September 4 and October 16, influenza A (H2N3) was isolated from 4 patients residing in Collier and Palm Beach counties.