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Update: Influenza Activity -- United States

Reports of influenza virus isolates received weekly at CDC from collaborating laboratories peaked in February and are now declining in parallel with morbidity indices of influenza (Figure 1) (1). A preliminary total of 1,317 influenza virus isolates has been reported this season through March 23, 1984; 807 (61%) were identified as type A(H1N1); 452 (34%) as type B; and 58 (4%) as type A(H3N2). One or more types of influenza virus have now been isolated in 49 states and the District of Columbia.

Although outbreaks in nursing homes have been uncommon this season, as most activity has been of type A(H1N1) virus among children or young adults, a few have been documented in association with types A(H3N2) or B infection. Five such outbreaks have been reported--three from California and one each from Massachusetts and Minnesota. The first began at a nursing home in San Bernadino at the end of December 1983, when 15 (31%) of 48 residents developed influenza-like illness. Serologic testing has shown diagnostic rises in titers to influenza type A(H3N2) in three of four patients. In late February, another influenza outbreak was noted in a Los Angeles hospital for elderly patients. Influenza-like illness affected 30 (38%) of the 80 patients, and one type B isolate was obtained. Further serologic studies also indicated type B infections. A small outbreak was reported early in March in San Francisco, where all 10 patients in one ward of a nursing hospital for the elderly developed influenza-like illnesses, and four type B isolates were identified. In Massachusetts, two type A(H3N2) virus isolates were obtained in March from an outbreak of influenza-like illness in a nursing home. In Minnesota, an outbreak of type B that began in mid-March was recently documented from a Hennepin County nursing home. Influenza-like illness affected 29 (23%) of the 200 residents, and type B was identified in four of six specimens collected. Reported by A Taylor, MPH, T Stephenson, MPH, San Bernadino County Health Dept, F Sorvillo, MPH, Los Angeles County Health Dept, B Louie, S Dritz, MD, San Francisco County Health Dept, J Schieble, PhD, R Murray, DrPH, California Dept of Health Svcs; J McDonough, Hennepin County, D Peterson, MPH, Minnesota Dept of Health; J DeCinti, MEd, Massachusetts Dept of Public Health; State Epidemiologists and Laboratory Directors; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, Systems Development Br, Computer Systems Office, Statistical Svcs Activity, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.


  1. CDC. Influenza Activity--Mississippi, United States, Worldwide. MMWR 1984:33;131-40.

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