Current Trends
Influenza Surveillance Summary, 1981-1982 Season
National data on influenza activity for the 1981-1982 season
were
obtained from three major sources: (a) weekly reports of mortality
from 121 cities, including the ratio of pneumonia and influenza (P
and
deaths to total deaths, an index of the relative mortality
attributable to influenza; (b) weekly reports of the number of
respiratory specimens tested and the number and types of influenza
isolates identified by 63 collaborating state, county, city, or
military laboratories, and (c) weekly semi-quantitative estimates
from
each state health department of the extent of influenza-like
morbidity
indicated by their individual statewide surveillance systems. In
addition, spontaneous reports of unusual cases and outbreaks of
influenza were received by CDC.
In terms of all the available criteria, the impact of influenza
was low in the 1981-1982 season. Mortality statistics did not show
a
national increase in the ratio of deaths associated with P and I
beyond the expected seasonal variation (Figure 1), despite presence
of
virus through May 1982 (Figure 2); widespread influenza activity
was
reported in only four states throughout the period of virus
circulation (Figure 3). In the preceding season, by way of
contrast,
the ratio of P and I deaths to total deaths was elevated for 13
weeks,
and 32 states reported widespread influenza activity. Both
influenza
type B and influenza type A(H1N1) viruses were commonly isolated
during the 1981-1982 season, but the total number of isolates
reported
to CDC by collaborating laboratories was approximately 600,
compared
with a range of 1,000 to 2,000 in the 5 preceding years (Figure 4).
Of the isolates obtained by the collaborating laboratories, 74%
were influenza type B virus; 23 states isolated only influenza type
B
virus. Seventeen states isolated both influenza B and influenza
A(H1N1) viruses, and one state isolated only influenza A(H1N1)
virus.
Influenza B virus outbreaks were first detected during the season
in
the southwestern states beginning January to February, then spread
east and north. By the end of the season, influenza B had been
identified in almost all regions of the country (Figures 5, 6).
Throughout the winter, influenza A(H1N1) virus was more prevalent
in
the southwestern and Pacific regions than elsewhere, although some
activity was detected in the eastern regions. Only a few influenza
A(H3N2) strains, associated with sporadic cases in Florida and
Texas,
were isolated from residents of the continental United States
during
the 1981-1982 season. In Nevada swine influenza-like virus was
isolated from an immunocompromised child (1).
The predominant influenza B and influenza A(H1N1) viruses were
frequently associated with reports of widely separated outbreaks
among
school children--typically with little evidence of community-wide
impact, as judged by minimal increases in absenteeism for entire
school districts and by lack of increases in numbers of hospital
emergency room visits for influenza-like illness. From about March
through May, occasional outbreaks of influenza B virus in nursing
homes were documented.
Reported by Immunization Div, Center for Prevention Svcs,
Consolidated
Surveillance and Communications Activity, Epidemiology Program
Office,
Influenza Br, Div of Viral Diseases, Center for Infectious
Diseases,
CDC.
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