Epidemiologic Notes and Reports Influenza A(H1N1) Associated
With Mild Illness in a Nursing Home -- Maine
Maine. On January 15, 1987, the Maine Bureau of Health was
notified of an outbreak of respiratory illness affecting residents
of
a central Maine nursing home. The nursing home is an intermediate
care facility housing 59 residents ranging from 17 to 93 years of
age
(median = 68 years). Influenza A/Taiwan/86(H1N1)-like virus was
isolated from two throat swabs obtained from ill residents on
January
16. The nursing home had offered the trivalent influenza vaccine
to
all residents and staff in November 1986; 50 (85%) residents and 14
(23%) of the 60 staff members had been vaccinated.
Eleven (19%) of the 59 residents met the case definition for
influenza-like illness (i.e., culture-confirmed influenza or fever
greater than or equal to 37.8 C (100 F) accompanied by at least one
respiratory symptom (cough, coryza, or sore throat)). The attack
rate
among vaccinated residents was 16% (8/50) compared with 33% (3/9)
among unvaccinated residents. The median age of cases was 68
years.
The index case was a 17-year-old female who experienced onset of
symptoms January 8; the last case occurred January 16. Only two
(3%)
of the 60 staff members reported an influenza-like illness during
the
corresponding time period. Most residents had clinically mild
cases,
and many were able to continue their usual activities during their
illnesses. The median duration of fever greater than or equal to
37.8 C (100 F) was 2.5 days. None of the ill residents were
hospitalized or developed complications such as pneumonia.
United States. For the week ending January 24, 10 states*
reported widespread outbreaks of influenza-like illness, and 18
states**, the District of Columbia, and Puerto Rico reported
regional
outbreaks of influenza-like illness. This is the fifth week with
more
than 20 states reporting outbreak activity.S
Influenza A/Taiwan/86(H1N1)-like virus continues to be the
predominant strain of influenza this season and represents 99% of
isolates reported from collaborating diagnostic laboratories.
Forty-seven states and the District of Columbia have now reported
isolates of influenza A(H1N1) virus**.
Reported by D Williams, A Littlefield, K Gensheimer, MD, State
Epidemiologist, Bur of Health, Maine Dept of Human Svcs; State and
Territorial Epidemiologists and State Laboratory Directors; WHO
Collaborating Center for Influenza, Influenza Br, Div of Viral
Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: A few sporadically occurring cases of
laboratory-confirmed influenza A(H1N1) have been reported in
nursing
home residents this season. The fact that this is the first
outbreak
of respiratory illness associated with influenza A(H1N1) in a
nursing
home that has been reported to CDC this season suggests that such
outbreaks are uncommon. Since laboratory diagnosis could not be
obtained for nine of the 11 cases in this outbreak, it is
impossible
to confirm that all cases of febrile respiratory illness were
caused
by influenza.
The mild illnesses overall and the lower attack rate in
vaccinated
residents suggest that A/Taiwan/86 infections were prevented or
abated
by prior exposure to type A(H1N1) strains or by vaccination with
the
A/Chile/83(H1N1) antigen in the trivalent influenza vaccine.
However,
because of the small number of unvaccinated residents and the lack
of
laboratory diagnosis for most cases, this hypothesis could not be
proven.
The observation that the illnesses were clinically mild, of
short
duration, and not associated with serious complications is
consistent
with clinical observations of laboratory-proven influenza A(H1N1)
infection in most other older adults. Furthermore, only 2.1% of
type
A(H1N1) virus isolates reported to CDC so far this season have been
from persons greater than or equal to 65 years of age. These
observations are consistent with those made during other influenza
seasons since 1977 in which A(H1N1) has predominated.
References:
ACIP. Monovalent influenza A(H1N1) vaccine, 1986-1987. MMWR
1986;35:518.
*Arizona, Colorado, Connecticut, Hawaii, New Hampshire, Oregon,
Tennessee, Texas, Washington, and Wyoming.
**Alabama, Alaska, Arkansas, California, Idaho, Iowa, Kansas,
Kentucky, Minnesota, Mississippi, Nebraska, New Mexico, North
Carolina, North Dakota, Pennsylvania, South Dakota, Utah, and
Wisconsin.
SRhode Island and Wyoming have not reported any influenza isolates
so
far this season. South Dakota has reported isolating influenza
type
A, subtype unspecified.
PInfluenza A(H1N1) stopped circulating in 1957 and reemerged in
1977
(1).
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