Current Trends Update: Influenza Activity -- United States
Reports of influenza viruses in the United States isolated by
the
collaborating diagnostic laboratories have increased sharply, with
over 200 viruses identified each week since the end of January
1986.
Overall, approximately 80% of the reported viruses have been type
B,
but more type A(H3N2) than type B viruses have been identified
among
persons older than 64 years. Of type B viruses, 66.3% have been
isolated from persons under 19 years old, and 3.2%, from persons
over
64 years old. In comparison, 45.9% of type A(H3N2) cases occurred
among persons under 19 years old; 26.1% occurred among persons over
64
years old. Forty-five states have now reported type B virus
isolates;
29 states, type A(H3N2) isolates; and 28 states, both types.
For the week ending February 22, 18 states reported widespread
outbreaks of influenza-like illness, and 15 states and the District
of
Columbia reported regional outbreaks. For the preceding week, 37
states had reported outbreak status, more than for any week since
January 1981. Tallies of patients with influenza-like illnesses
seen
by the network of family physicians* nationwide averaged 10.9 cases
for the reporting week ending February 12, compared with the 11.5
average for the preceding week and the maximum values of 11-12
cases
for the two preceding seasons (Figure 1).
The percentage of pneumonia and influenza deaths reported from
the
121 U.S. cities for the week ending February 22 was 6.3%, compared
with 6.2% for the preceding week (Figure 1).
Reported by State and Territorial Epidemiologists; State Laboratory
Directors; Statistical Svcs Br, Div of Surveillance and
Epidemiologic
Studies, Div of Field Svcs, Epidemiology Program Office, WHO
Collaborating Center for Influenza, Influenza Br, Div of Viral
Diseases, Center for Infectious Diseases, CDC.
*Cases reported by those members of the American Academy of Family
Physicians Research Panel who serve as sentinel physicians for
influenza.
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