Update: Influenza Activity -- United States, 1991-92

From late October through November 20, 1991, state health departments reported outbreaks of culture-confirmed influenza A(H3N2) in public schools in Texas and a university in Tennessee. In addition, Alabama, Georgia, Minnesota, North Carolina, Ohio, and Tennessee reported outbreaks of culture-confirmed influenza A (not subtyped) in schools. In these outbreaks, school absentee rates ranged from 11% to 40%; school closures were reported in Ohio and Tennessee.

As of November 20, sentinel physicians in most regions of the United States reported that 1%-5% of patient visits were for influenza-like illness, a rate that was stable. However, in states in the Middle Atlantic and West South Central regions, rates had increased to greater than or equal to 8% from a baseline of 3%-4%.

As of November 20, a total of 74 influenza isolates had been reported to CDC from World Health Organization Collaborating Laboratories and Health Care Financing Administration Influenza Vaccine Demonstration Surveillance laboratories. Seventy-three (99%) were influenza A: of these, 36 (49%) were A(H3N2); three (4%), A(H1N1); and 34 (47%), A (not subtyped). One isolate was influenza B.

From September 1 through November 20, isolates of influenza A(H3N2) were reported from Alaska, Florida, Georgia, Illinois, Louisiana, Minnesota, Oklahoma, Tennessee, and Texas; of influenza A(H1N1) from Georgia, Hawaii, New York, Pennsylvania, and Texas; of influenza A (not subtyped) from Alabama, Alaska, Arizona, Arkansas, Georgia, Hawaii, Illinois, Massachusetts, Michigan, Minnesota, Mississippi, New York, North Carolina, Ohio, Oregon, Pennsylvania, and Texas; and of influenza B from Texas.

Isolates of influenza A(H3N2) from Alabama, Alaska, Florida, Louisiana, Tennessee, and Texas have been characterized at CDC as similar to A/Beijing/353/89. A/Taiwan/1/86-like influenza A(H1N1) has been identified from Hawaii and Texas. Reported by: Epidemiology Activity, Office of the Director, and WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, Influenza Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: For the 1991-92 influenza season, the level and pattern of national influenza activity has been unusual for at least two reasons. First, in the United States, community outbreaks of influenza in several different regions of the country rarely occur before December. Second, influenza A(H3N2), predominant among influenza viruses subtyped this season, is usually associated with outbreaks among adults in addition to schoolchildren; however, outbreaks among adults can be anticipated as the season progresses.

Persons at high risk for complications of influenza infection (including all persons aged greater than or equal to 65 years, persons with chronic pulmonary or cardiovascular disorders, and children and teenagers on long-term aspirin therapy) are encouraged to be vaccinated with the 1991-92 influenza vaccine. In the event of an influenza A outbreak in institutions where high-risk persons reside, chemoprophylaxis with amantadine should be initiated as early as possible to reduce the spread of the infection. Contingency planning is important to ensure rapid administration of amantadine to residents and employees (1,2).

Summaries of the changing national influenza surveillance data are updated weekly throughout the influenza season and available by computer to subscribers to the Public Health Network and to the public through the CDC information line, (404) 332-4555.

References

1. ACIP. Prevention and control of influenza: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-6).

2. CDC. Update: influenza activity--worldwide, 1990-91, and influenza vaccination--United States. MMWR 1991;40:709-12.

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