Update: Influenza Activity -- United States, 1989-90
Widespread influenza-like illness activity* for the 1989-90
influenza season was first reported the week ending December 16,
1989, in Montana and Utah. Four states (Mississippi, Montana,
Texas, and Utah) reported widespread activity during the week
ending December 30, and 10 states reported widespread activity
during the week ending January 6, 1990. For the week ending
January 13, 10 states reported widespread activity, 19 reported
regional activity, and 22 reported sporadic
activity (Figure 1).
Visits to approximately 110 sentinel family practice physicians
in 43 states for treatment of influenza-like illnesses have
similarly increased, accounting for 9.5%, 8.8%, and 10.3% of all
visits during the weeks ending December 30, January 6, and
January 13, respectively, compared with a mean of 4.9% during the
4 weeks ending December 23. Approximately 3% of all patients seen
by sentinel physicians for treatment of influenza-like illness
have required hospitalization. Persons greater than or equal to
65 years of age are more likely to be hospitalized for
influenza-like illness or complications than are persons less
than 65 years of age (13.7% vs. 2.0%).
Influenza A(H3N2) continues to be the predominant influenza
strain, accounting for approximately 98% of the 335 isolates
subtyped and reported to CDC so far this season. Influenza has
been isolated in patients from all age groups. Culture-confirmed
outbreaks of influenza A(H3N2) in nursing home residents have
been reported from seven states. Since December 15, outbreaks of
respiratory illness in 68 (21%) of 329 Connecticut nursing homes
have been reported to the state health department; influenza A
viruses have been isolated from patients at six of these nursing
homes.
In the 121 cities that report death certificate data regularly
to CDC, 7.6% of deaths were associated with pneumonia and
influenza for the week ending January 13. This percentage exceeds
the epidemic threshold of 6.7% for the first time this influenza
season.
Reported by: ML Cartter, MD, JL Hadler, MD, State Epidemiologist,
Connecticut State Dept of Health Svcs. State and territorial
health department epidemiologists and state laboratory directors.
WHO Collaborating Laboratories. Sentinel Physicians of the
American Academy of Family Practice. Div of Surveillance and
Epidemiologic Studies, Epidemiology Program Office; Epidemiology
Office, Biometrics Activity, Influenza Br, Div of Viral and
Rickettsial Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: During influenza A outbreaks in nursing homes and
other chronic-care facilities, the combined use of influenza
vaccination and amantadine prophylaxis and treatment of both
residents and employees may shorten the duration and severity of
the outbreak (1-3). However, amantadine-resistant influenza
viruses can emerge when amantadine is used for treatment (4-6).
The frequency with which resistant isolates emerge and the extent
of transmission of these viruses remain unknown; however, there
is no evidence to suggest that amantadine-resistant viruses are
more virulent or more transmissible than amantadine-sensitive
viruses (5). Thus, the use of amantadine remains an appropriate
outbreak-control measure.
In closed populations such as nursing homes, ill persons who
are receiving amantadine as treatment should be separated,
whenever possible, from persons receiving amantadine as
prophylaxis against influenza. The continued occurrence of
influenza-like illness in an institution where amantadine is
being used, and isolation of influenza viruses from persons who
are receiving amantadine, should be reported through the state
health department to CDC.
References
ACIP. Prevention and control of influenza. MMWR
1988;37:361-4,369-73.
Atkinson WL, Arden NH, Patriarca PA, Leslie N, Lui KJ, Gohd R.
Amantadine prophylaxis during an institutional outbreak of type
A(H1N1) influenza. Arch Intern Med 1986;146:1751-6.
Mostow SR. Prevention, management and control of influenza:
role of amantadine. Am J Med 1987;82(suppl 6A):35-41.
Mast EE, Davis JP, Harmon MW, Arden NH, Circo R, Tyszka GE.
Emergence and possible transmission of amantadine-resistant
viruses during nursing home outbreaks of influenza A(H3N2)
(Abstract). In: Program and abstracts of the twenty-ninth
Interscience Conference on Antimicrobial Agents and Chemotherapy.
Washington, DC: American Society for Microbiology, 1989:111.
Belshe RB, Burk B, Newman F, Cerruti RL, Sim IS. Resistance of
influenza A virus to amantadine and rimantadine: results of one
decade of surveillance. J Infect Dis 1989;159:430-5.
Hayden FG, Belshe RB, Clover RD, Hay AJ, Oakes MG, Soo W.
Emergence and apparent transmission of rimantadine-resistant
influenza A virus in families. N Engl J Med 1989;321:1696-1702.
*Levels of activity are: 1) Sporadic--sporadically occurring
influenza-like illness or culture-confirmed influenza, with no
outbreaks detected; 2) Regional--outbreaks of influenza-like
illness or culture-confirmed influenza in counties having a
combined population of less than 50% of the state's total
population; 3) Widespread--outbreaks of influenza-like illness or
culture-confirmed influenza in counties having a combined
population of greater than or equal to 50% of the state's total
population.
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