Epidemiologic Notes and Reports Update: Influenza Activity -- United States

Indicators of influenza activity are increasing throughout the United States. For the week ending January 23, 1988, 2 states* reported widespread outbreaks of influenza- like activity, and 10 states** reported regional influenza-like activity. This is the second week with reports of widespread influenza-like activity. For the report week ending January 16, 1988, physicians*** reported that 6% of their outpatients were diagnosed as having influenza-like illness. While this level is the highest reported so far this year, it is below the usually observed peak of 10%-12%.

Influenza A(H3N2), the predominant type this season, has now been identified in 25 states**** (Figure 1). Eight states have reported isolates of influenza A, subtype pending.***** Outbreaks of influenza A(H3N2) have now been documented in nursing homes in Minnesota, New York, and Wisconsin. In addition, an outbreak of influenza- like illness began during late December and continued into January in a facility for the mentally handicapped in South Dakota; both residents and staff were affected. South Dakota also reported an abrupt increase in school absenteeism due to influenza-like illness among students and staff. Sporadically occurring cases of Influenza B occurring cases of influenza B have been reported from 6 states;****** however, influenza B has not been associated with any outbreaks.

In the 121 cities reporting regularly to CDC, 5.9% of deaths were associated with pneumonia and influenza (P&I) for the week ending January 16, 1988. This percentage does not exceeded the epidemic threshold******* for the influenza season to date (Figure 2). Reported by: Participating State and Territorial Epidemiologists and State Laboratory Directors. Sentinel Physicians of the American Academy of Family Physicians. WHO Collaborating Laboratories. WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Reference

1. Lui K-J, Kendal AP. Impact of influenza epidemics on mortality in the United States from October 1972 to May 1985. Am J Public Health 1987;77:712-6. 

* Hawaii and South Dakota. 

**Idaho, Kentucky, Mississippi, Missouri, Montana, Nebraska, Texas, Utah, Washington, and Wisconsin. 

***Reported by approximately 160 physician members of the American Academy of Family Physicians. A patient with a temperature greater than or equal to37.8 degrees C (100 degrees F) and at least cough or sore throat was considered to have influenza-like illness. 

****Arizona, California, Colorado, Florida, Idaho, Iowa, Kansas, Michigan, Minnesota, Missouri, Montana, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Tennessee, Texas, Utah, Washington, Wisconsin, and Wyoming. 

*****Hawaii, Indiana, Kentucky, Louisiana, Nebraska, Mississippi, North Carolina, and Virginia. 

******Arizona, Hawaii, Montana, New York, Ohio, and Tennessee. 

*******The epidemic threshold for the 1987/88 influenza season was estimated at 1.645 standard deviations above the values projected on the basis of a periodic regression model applied to observed P?&I deaths for the previous 5-year period, but excluding the observations during influenza outbreaks (1).

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