Morbidity reports show a continued increase in the number of
outbreaks of influenza-like illness in the United States. In most
cases for which laboratory results have been obtained, influenza
type
A(H1N1) has been isolated. The greatest spread of type A(H1N1)
virus
has occurred in the South Atlantic and South Central states.
Preliminary results indicate that, in January, separate school
outbreaks of influenza types A(H1N1) and B occurred in Hennepin
County, Minnesota. The influenza type B outbreak was the first
reported in the country this season. Following an almost total
absence of type A(H3N2) virus isolates after the outbreaks in
Alaska
in November/December 1983, isolates have recently been reported
from
patients with sporadic cases in Arizona, New Mexico, and
Pennsylvania.
Thus far in the 1983-1984 season, isolates of type A(H1N1)
virus
have been reported from the District of Columbia and 20 states:
Alabama, Alaska, Arizona, Arkansas, California, Colorado, Florida,
Georgia, Hawaii, Iowa, Louisiana, Maine, Massachusetts, Minnesota,
Nevada, New Mexico, New York, North Carolina, South Carolina, and
Texas; with associated outbreaks reported from Arizona, Arkansas,
Georgia, Iowa, Louisiana, Minnesota, New Mexico, New York, North
Carolina, South Carolina, and the District of Columbia. Isolates
of
type B virus have been reported from 13 states: Arizona, Arkansas,
California, Colorado, Hawaii, Minnesota, Nevada, New Mexico, New
York,
Oregon, Texas, Washington, and West Virginia; with associated
outbreaks reported from Minnesota, and possibly Texas. Isolates of
type A(H3N2) virus have been reported from Alaska, Arizona, New
Mexico, Pennsylvania, and Tennessee; associated outbreaks were
reported from Alaska at the end of 1983.
Reported by C Hedburg, Hennepin County Health Dept, D Peterson, MS,
D
Stiepan, J Braun, AG Dean, MD, State Epidemiologist, Minnesota Dept
of
Health; State Epidemiologists and Laboratory Directors; Div of
Field
Svcs, Epidemiology Program Office, Statistical Svcs Activity,
Influenza Br, Div of Viral Diseases, Center for Infectious
Diseases,
CDC.
Editorial Note
Editorial Note: Since 1977, type A(H1N1) virus has twice caused
epidemics in children and young adults--in 1977-1978 and 1978-1979.
Although related viruses have been isolated in each succeeding
year,
they have not caused widespread outbreaks again until this year.
Several factors probably contribute, including waning levels of
immunity among those infected during the 1977-1979 outbreaks and
evolution of new variant strains (1). When multiple virus types
circulate (i.e., type A(H1N1), type A(H3N2), and type B viruses),
the
relative prevalence of the different virus strains can alter during
the course of the season and may vary between regions. Outbreaks
caused by several virus types are also possible. Continued
laboratory
diagnosis is especially important under current circumstances.
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