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Current Trends Update: Influenza Activity -- United States

Reports of influenza cases from family physicians' practices and of morbidity levels from the states and collaborating diagnostic laboratories indicate that 1985-1986 national influenza activity has peaked in the United States.

Reports of influenza-like illnesses from the practices of sentinel physicians* for the week ending February 19 averaged 11.1 compared with the averages of 10.9 and 11.6 reported for the preceding weeks. Outbreaks of influenza-like illness were reported by 25 states for the week ending March 1, a decrease from the total of 33 states that reported outbreaks for the preceding week. Fourteen states indicated widespread outbreaks (Figure 2); 11 states and the District of Columbia indicated regional outbreaks.

The numbers of type B virus isolates reported by the collaborating laboratories have peaked. Incomplete totals for the week ending February 22 include 171 type B and 39 type A(H3N2) isolates; 249 type B viruses and 65 type A(H3N2) viruses were reported for the week ending February 15. Overall, 1,538 influenza virus isolates, including 79.3% type B viruses and 20.7% type A(H3N2) viruses, have been reported this season.

The percentage of pneumonia and influenza (P&I) deaths reported from the 121 U.S. cities for the week ending March 1 was 6.3%, the same percentage reported for the preceding week. This is the eighth consecutive week the P&I percentage has exceeded the statistical limit expected in the absence of influenza outbreaks nationwide. Preliminary data for the current season indicate that the age distribution of P&I deaths is similar to that observed for the 1984-1985 influenza season.

Many outbreaks of influenza in schools have been associated with type B virus, and a mixed outbreak of types A(H3N2) and B viruses in a North Carolina college was reported earlier (1). Laboratory evidence of a college outbreak associated primarily with type A(H3N2) has now been reported from Alabama; type A(H3N2) influenza viruses were isolated from eight of 10 ill students tested at Samford University's student health clinic in Birmingham during an outbreak that began in late January and continued into mid-February. Reported by J Shaw, MPA, WJ Alexander, MD, Jefferson County Health Dept, B Edwards, Birmingham Br Laboratory, Alabama State Dept of Public Health; State and Territorial Epidemiologists; State Laboratory Directors; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Div of Field Svcs, Epidemiology Program Office, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note:As the data above demonstrate, influenza activity is now peaking or declining in most regions of the country. Reports of P&I-associated deaths typically lag several weeks behind reports of influenza illness and viral diagnostic results. Consequently, the P&I percentages reported from the 121 cities may continue near the current levels in the near future while other indices of influenza activity decline.

Reference

  1. CDC. Update: influenza activity--United States. MMWR 1986;35:65-6. *Cases reported by those members of the American Academy of Family Physicians Research panel who serve as sentinel physicians for influenza.

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