INFLUENZA VIRUS SURVEILLANCE SUMMARY UPDATE

Week ending April , 2003-Week 13

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

Florida: During week 13 (March 23-29, 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 1.48%. 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, Orange, Palm Beach and Polk counties.**  Light to moderate influenza activity was seen in nine other counties   During the last three weeks (weeks 11 – 13) seven laboratory confirmed influenza cases. (primarily influenza A (H1N1) and influenza B) were reported from four counties across the state. This week influenza A H1N1 viruses were reported Broward county, influenza A of unknown subtype from Broward county and influenza B from Indian River county. 

National report: During week 13, ninety-four isolates (75 influenza A and 19 influenza B viruses) were made from 1,465 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 7.6% during Week 13.  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 1.2% nationwide. The State and Territorial Epidemiologists in 19 states (Alaska, Arizona, California, Colorado, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, North Dakota, Ohio, Oregon, South Carolina, South Dakota, Tennessee, Utah, and Wisconsin) reported regional influenza activity. No flu outbreaks were reported. Twenty-eight states reported sporadic influenza activity, and 2 states reported no influenza activity.   During the past 3 weeks (weeks 11-13), between 5.3% and 10.7% of the specimens tested for influenza in the West South Central, East South Central, Pacific, and South Atlantic regions were positive, 27.4% of the specimens tested for influenza in the New England region were positive, between 14.2% and 19.8% of specimens tested for influenza in the West North Central, Mountain, and East North Central regions were positive, and less than 5% of specimens tested for influenza in the Mid-Atlantic region were positive.  Since September 29, 11.8% (n=8,791) of the 74,790 specimens tested nationwide have been positive. Two thousand one hundred and eighty-nine (49%) of the 4,513 influenza A viruses have been subtyped; 1,661 (76%) were influenza A (H1) viruses and 528 (24%) were influenza A (H3N2) viruses.  Laboratory confirmed influenza has been reported from all 50 states.  Influenza B viruses were reported more frequently than influenza A viruses (range 59% - 83%) in the West South Central, South Atlantic, West North Central, and East South Central regions. 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. However, during the past 3 weeks (weeks 11-13), 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 71 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.

**The higher than normal Orange county ILI reflects the report of a single surveillant.  We seek additional surveillants for that area.

 
For additional information on influenza and influenza surveillance results, please visit our website at http://www.doh.state.fl.us/disease_ctrl/epi/htopics/flu/index.htm