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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

  1. ACIP. Prevention and control of influenza. MMWR 1988;37:361-4,369-73.

  2. 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.

  3. Mostow SR. Prevention, management and control of influenza: role of amantadine. Am J Med 1987;82(suppl 6A):35-41.

  4. 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.

  5. 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.

  6. 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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