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Update: Influenza Activity -- United States

Influenza virus activity continues in all regions of the United States. An excess in the ratio of deaths from pneumonia and influenza (P&I) to total deaths was recorded from 121 cities for the seventh consecutive week. The ratio of P&I deaths for the week ending February 26, 1983, was 5.5, and the expected ratio was 4.1. Five states (Iowa, Missouri, Nebraska, Ohio, and Texas) reported widespread activity, and 12 states reported regional influenza activity for the week ending February 26.

Iowa, North Carolina, and South Carolina have now reported their first isolations of the season, all influenza type A(H3N2), making a total of 40 states with reported influenza isolates. Although the majority of isolates reported continues to be type A(H3N2) virus, the proportion of type A(H1N1) virus isolates has increased in recent weeks, and 13 states have now reported isolates of H1N1 virus. Influenza type B virus has been isolated from sporadic cases in five states.

The Ohio State Department of Health has provided a comparison of outbreaks associated with H3N2 and with H1N1 viruses. The Ohio State Diagnostic Laboratory documented the parallel activity of H3N2 and H1N1 viruses near Columbus, Ohio, in late January and the first 2 weeks of February. An outbreak of influenza, with a peak absentee rate of 20% in a parochial elementary school in the Columbus area, was followed approximately 10 days later by a similar outbreak, with an absentee rate of 27%, in another parochial elementary school located six miles away. In the first outbreak, four influenza type A(H3N2) virus isolates were recovered from specimens collected from seven ill pupils, and in the second outbreak, three influenza type A(H1N1) virus isolates were recovered from six ill pupils. Typical of the illnesses in each school were cases of typical influenza with abrupt onset and temperatures occasionally higher than 39.4 C (103 F). Each school was closed for 1 day at the height of its outbreak, and each reported a return to a normal level of illness within a week. Other school outbreaks occurred, and by the week ending February 19, nine parochial schools were closed in Franklin County, and absentee rates up to 27% were reported in Columbus city schools. Isolates of both H1N1 and H3N2 viruses have also been identified from children in the Dayton area, where several schools were closed in February due to influenza-like illness. Whether other outbreaks of influenza among schoolchildren, now being reported by several states, involve H1N1 or H3N2 virus infections or a mixture of both has not been determined. However, during recent years, investigations of outbreaks involving older patients, such as those in nursing homes, have shown H3N2 or type B influenza virus rather than H1N1 virus as the cause. Reported by JP Baxa, K Sullivan, G Davidson, DrPH, MW Plummer, B Stimpert, T Halpin, MD, State Epidemiologist, Ohio State Dept of Health; Respective state epidemiologists and laboratory directors; Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

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