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Influenza -- United States, 1984-1985 Season

Influenza type A (H3N2) viruses were isolated in every state during the 1984-1985 season and were associated with the highest ratio of pneumonia and influenza deaths (as a percentage of total deaths) since 1976. Low levels of influenza B activity occurred late in the season, and influenza A(H1N1) virus was reported rarely.

National data on influenza activity for the 1984-1985 season were obtained from four major sources: (1) weekly reports of the number of respiratory specimens tested and the number and types of influenza virus isolates identified by 61 collaborating state, county, city, or military laboratories; (2) weekly reports of mortality from 121 cities, including deaths associated with pneumonia and influenza (P&I), an index that has historically reflected seasonal mortality attributable to influenza; (3) weekly semiquantitative estimates from each state health department of the extent of influenza-like morbidity indicated by its statewide surveillance system; and (4) weekly returns from approximately 125 physician members of the American Academy of Family Physicians Research Panel, who recorded the number of patients seen in their offices with influenza-like illnesses. In addition, CDC also received spontaneous reports of unusual influenza cases and outbreaks from a variety of sources.

Isolates of type A(H3N2) virus were first associated with sporadic cases in Nevada in November and in the New York City area, Texas, and Wisconsin by early December. The first laboratory-documented outbreak of the season also began in early December (a kindergarten class in California), and by late December, type A(H3N2) outbreaks had been confirmed in a prison and a nursing home in New York City and in an elementary school, a college, and a Veterans Administration hospital in Illinois. By January 31, isolates of influenza type A(H3N2) had been reported from all but nine states, and by the end of the season, influenza A(H3N2) virus had been reported from every state and the District of Columbia (Figure 2). The peak of virus isolations occurred in February, in parallel with peaks in physician reports of influenza morbidity, and the highest P&I mortality ratios also occurred in February (Figure 3).

During the season, 36 states reported regional or widespread outbreaks (Figure 4), compared with 37 for the previous season. The percentage of deaths attributed to P&I reached a maximum of 7.2% in late February and early April; this was the highest percentage since 1976, when it reached 7.7%.

Approximately 2,100 isolates were reported by collaborating laboratories, close to the total for the 1983-1984 season and above the average of about 1,500 isolates for the preceding five seasons (Figure 5). Type A(H3N2) viruses predominated, accounting for 97% of the reported isolates. Type B viruses accounted for almost all the remaining 3% of viruses reported. In addition to sporadic cases, type B isolates were associated with two school outbreaks in Hawaii and an outbreak in a geriatric ward in a New York hospital during April. Only a few type A(H1N1) isolates were identified during the season, all from sporadic cases. Reported by State and Territorial Epidemiologists and State Laboratory Directors; U.S. School of Aerospace Medicine, San Antonio, R Couch, MD, P Glezen MD, and H Six, PhD, Baylor College of Medicine, Houston, Brooke Army Medical Center, Fort Sam Houston, Texas; Milwaukee Health Dept Virus Laboratory, Milwaukee, Wisconsin; Allegheny County Health Laboratory, Pittsburgh, Pennsylvania; Sunrise Hospital Virology Laboratory, Las Vegas, Nevada; Montefiore Hospital and Medical Center Virus Laboratory, New York City, Nassau County Medical Center Virology Laboratory, East Meadow, Erie County Medical Center Virology Laboratory, Buffalo, University of Rochester Medical Center, Rochester, New York; Charity Hospital Virology and Rickettsial Laboratory, New Orleans, Louisiana; Mayo Clinic Virology Laboratory, Rochester, Minnesota; Veterans Administration Hospital Virus Laboratory, West Haven, Connecticut; Department of Pediatrics, University of Chicago, Illinois; University of Arizona Health Service Center Virology Laboratory, Tucson, Arizona; Letterman Army Medical Center, San Francisco, Los Angeles County Health Department Virology Laboratory, Los Angeles, California; University of Colorado Medical Center Virus Laboratory, Denver, Colorado; Participating physicians of the American Academy of Family Physicians; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

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