Influenza outbreaks in schools and colleges, associated with
influenza types A(H1N1) or B, have occurred in all regions of the
United States this year. However, there has been no consistent
elevation of deaths attributable to pneumonia and influenza in the
121
reporting cities through mid-February, suggesting that older
populations have been only slightly affected by the outbreaks.
A cumulative total of 590 influenza virus isolates has been
reported this season through February 10, 1984; 381 (65%) were
identified as type A(H1N1); 171 (29%), as type B; and 38 (6%), as
type
A(H3N2) (Figure 3). Results of virus laboratory testing are
reported
according to three broad age categories--patients less than 31
years
of age, patients 31-65 years of age, and patients over 65 years of
age. Of the 7,125 specimens tested by February 10 for which ages
of
patients were reported, 85%, 10%, and 5%, respectively, were from
patients in these age brackets. Ninety-seven percent of the
A(H1N1)
isolates have been from persons in the youngest age group,
representing 5% of specimens tested from these persons. In
contrast,
0.5% of specimens from persons over 65 years of age were positive
for
A(H1N1) virus. In 1982-1983, however, when activity was
predominantly
caused by type A(H3N2) virus, 62% of A(H3N2) isolates were from
persons in the youngest age group, and the proportion of specimens
positive for influenza type A(H3N2) increased from 7% in the
under-31-years group to 20% in the over-65-years group. While
findings for the current season may change, the preliminary results
are consistent with the paucity of reported outbreaks of influenza
among the elderly this year, despite the prevalence of type A(H1N1)
outbreaks in younger age groups.
Reported by State Epidemiologists and Laboratory Directors;
Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies,
Epidemiology Program Office, Statistical Svcs Activity, Influenza
Br,
Div of Viral Diseases, Center for Infectious Diseases, CDC.
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