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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.
Disclaimer
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