Influenza type A (H3N2) viruses were isolated in every state
during the 1984-1985 season and were associated with the highest
ratio
of pneumonia and influenza deaths (as a percentage of total deaths)
since 1976. Low levels of influenza B activity occurred late in
the
season, and influenza A(H1N1) virus was reported rarely.
National data on influenza activity for the 1984-1985 season
were
obtained from four major sources: (1) weekly reports of the number
of
respiratory specimens tested and the number and types of influenza
virus isolates identified by 61 collaborating state, county, city,
or
military laboratories; (2) weekly reports of mortality from 121
cities, including deaths associated with pneumonia and influenza
(P&I), an index that has historically reflected seasonal mortality
attributable to influenza; (3) weekly semiquantitative estimates
from
each state health department of the extent of influenza-like
morbidity
indicated by its statewide surveillance system; and (4) weekly
returns
from approximately 125 physician members of the American Academy of
Family Physicians Research Panel, who recorded the number of
patients
seen in their offices with influenza-like illnesses. In addition,
CDC
also received spontaneous reports of unusual influenza cases and
outbreaks from a variety of sources.
Isolates of type A(H3N2) virus were first associated with
sporadic
cases in Nevada in November and in the New York City area, Texas,
and
Wisconsin by early December. The first laboratory-documented
outbreak
of the season also began in early December (a kindergarten class in
California), and by late December, type A(H3N2) outbreaks had been
confirmed in a prison and a nursing home in New York City and in an
elementary school, a college, and a Veterans Administration
hospital
in Illinois. By January 31, isolates of influenza type A(H3N2) had
been reported from all but nine states, and by the end of the
season,
influenza A(H3N2) virus had been reported from every state and the
District of Columbia (Figure 2). The peak of virus isolations
occurred in February, in parallel with peaks in physician reports
of
influenza morbidity, and the highest P&I mortality ratios also
occurred in February (Figure 3).
During the season, 36 states reported regional or widespread
outbreaks (Figure 4), compared with 37 for the previous season.
The
percentage of deaths attributed to P&I reached a maximum of 7.2% in
late February and early April; this was the highest percentage
since
1976, when it reached 7.7%.
Approximately 2,100 isolates were reported by collaborating
laboratories, close to the total for the 1983-1984 season and above
the average of about 1,500 isolates for the preceding five seasons
(Figure 5). Type A(H3N2) viruses predominated, accounting for 97%
of
the reported isolates. Type B viruses accounted for almost all the
remaining 3% of viruses reported. In addition to sporadic cases,
type
B isolates were associated with two school outbreaks in Hawaii and
an
outbreak in a geriatric ward in a New York hospital during April.
Only a few type A(H1N1) isolates were identified during the season,
all from sporadic cases.
Reported by State and Territorial Epidemiologists and State
Laboratory
Directors; U.S. School of Aerospace Medicine, San Antonio, R Couch,
MD, P Glezen MD, and H Six, PhD, Baylor College of Medicine,
Houston,
Brooke Army Medical Center, Fort Sam Houston, Texas; Milwaukee
Health
Dept Virus Laboratory, Milwaukee, Wisconsin; Allegheny County
Health
Laboratory, Pittsburgh, Pennsylvania; Sunrise Hospital Virology
Laboratory, Las Vegas, Nevada; Montefiore Hospital and Medical
Center
Virus Laboratory, New York City, Nassau County Medical Center
Virology
Laboratory, East Meadow, Erie County Medical Center Virology
Laboratory, Buffalo, University of Rochester Medical Center,
Rochester, New York; Charity Hospital Virology and Rickettsial
Laboratory, New Orleans, Louisiana; Mayo Clinic Virology
Laboratory,
Rochester, Minnesota; Veterans Administration Hospital Virus
Laboratory, West Haven, Connecticut; Department of Pediatrics,
University of Chicago, Illinois; University of Arizona Health
Service
Center Virology Laboratory, Tucson, Arizona; Letterman Army Medical
Center, San Francisco, Los Angeles County Health Department
Virology
Laboratory, Los Angeles, California; University of Colorado Medical
Center Virus Laboratory, Denver, Colorado; Participating physicians
of
the American Academy of Family Physicians; Statistical Svcs Br, Div
of
Surveillance and Epidemiologic Studies, Epidemiology Program
Office,
Influenza Br, Div of Viral Diseases, Center for Infectious
Diseases,
CDC.
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