INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending April 5 , 2003-Week 14

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

Melissa Covey

Florida: During week 14 (March 30-April 5, 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 1.25%. This is lower than the national baseline of 1.9%. Higher flu activity than expected for this time of year (>2%) was reported by physicians in Indian River and Palm Beach counties.  Light to moderate influenza activity was seen in ten other counties.   During the past three weeks (weeks 12 – 14) three laboratory confirmed influenza cases (primarily influenza B) were reported from two counties across the state. This week one influenza A H1N1 virus was reported in Palm Beach county and one influenza B from Broward county. 

National report: During week 14, eighty-eight isolates (73 influenza A and 15 influenza B viruses) were made from 1,067 specimens tested by the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories this week.   The proportion of deaths attributed to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.9% during Week 14.  This percentage is below the epidemic threshold of 8.1% for this time. The proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 0.8% nationwide. The State and Territorial Epidemiologists in 10 states (Colorado, Idaho, Maine, Maryland, Minnesota, Montana, Nevada, North Dakota, Ohio, and Utah). Thirty-two states and New York City reported sporadic activity, and 5 states reported no influenza activity.

During the past 3 weeks (weeks 12-14), between 20.0% and 28.3% of the specimens tested for influenza in the New England and East North Central regions were positive, between 13.4% and 13.9% of specimens tested for influenza in the Mountain and West North regions were positive, and between 2.3% and 7.4% of the specimens tested for influenza in the West South Central, Mid-Atlantic, East South Central, Pacific, and South Atlantic regions were positive.

Since September 29, 12.0% (n=9,728) of the 80,968 specimens tested nationwide have been positive.  Two thousand six hundred and twenty-three (50%) of the 5,243 influenza A viruses have been subtyped; 2,069 (79%) were influenza A (H1)† viruses and 563 (21%) were influenza A (H3N2) viruses.  Laboratory confirmed influenza has been reported from all 50 states.  Influenza A viruses were reported more frequently than influenza B viruses (range 56% - 88%) in the New England, East North Central, Mountain, Pacific, and Mid-Atlantic regions, and influenza B viruses were reported more frequently than influenza A viruses (range 59% - 85%) in the South Atlantic, West North Central, West South Central, and East South Central regions. However, during the past 3 weeks (weeks 12-14), influenza A activity has increased to the point that during those weeks, influenza A viruses were reported more frequently than influenza B viruses in all nine surveillance regions.  CDC has characterized 76 influenza A (H1N1), 27 influenza A (H1N2), 63 influenza A (H3N2) and 188 influenza B isolates antigenically. The neuraminidase typing for 123 H1 viruses is pending.  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). 

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. 

* Reporting is incomplete for this week. Numbers may change as more reports are received.