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Update: Influenza Activity -- United States -- and the Role of Rapid Virus Typing in Improving Amantadine Use

Between December 30, 1985, and January 13, 1986, 27 (36%) of 74 elderly residents in a San Joaquin County, California, nursing home developed influenza-like illnesses.* Influenza virus type B was isolated from two of the five ill residents tested. This is the first report of a nursing-home outbreak this season associated with type B virus; an earlier report described outbreaks associated with type A(H3N2) virus in health-care facilities for elderly patients in New York (1).

Nine additional states have reported their first influenza virus isolations for the season. Type B virus has been reported from Alabama, Florida, Idaho, Louisiana, Missouri, New Jersey, and Oregon; type A(H3N2) virus has been reported from New Mexico and Oklahoma. In New York and Nevada, where type A(H3N2) virus had been reported previously this season, type B virus was also reported. The season's first influenza virus isolates have also been reported from sporadic cases in New York City; type A(H3N2) viruses have been isolated from residents of Brooklyn and the Bronx.

Tallies of patients** with influenza-like illnesses seen by sentinel physicians nationwide increased from an average of 6.1 for the reporting week ending January 1, 1986, to an average of 8.4 for the week ending January 8. Similar increases have been observed in recent seasons concurrently with the spread of influenza outbreaks.

The percentages of deaths from the 121 cities that were associated with pneumonia and influenza were 5.7% and 6.0% for the weeks ending January 11 and January 18, compared with the range of 4.9%-5.4% for the 4 preceding weeks. Reported by State and Territorial Epidemiologists; State Laboratory Directors; W Owings, MD, Centreville, Alabama; D Pates, MD, Rupert, Idaho; J Clark, M Earling, MD, Sunrise Hospital, R Weisner, MD, Las Vegas, Nevada; K Bromberg, MD, Kings County Hospital, I Spigland, MD, Montefiore Hospital, New York City, S Lipson, PhD, K Szabo, MD, Virus Laboratory, Naussau County, New York; participating physicians of the American Academy of Family Physicians; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Div of Field Svcs, Epidemiology Program Office, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The antiviral drug, amantadine hydrochloride, is highly effective in preventing illness caused by influenza type A viruses and has been recommended by the Immunization Practices Advisory Committee (ACIP) as an adjunct to vaccination in the control of influenza A infections (2). Amantadine is not effective against influenza type B viruses or other respiratory pathogens. Although amantadine seldom causes serious side effects in healthy, younger adults, it is more likely to cause troublesome side effects in older persons. When the normal adult dose of 200 mg daily has been reduced to 100 mg in individuals 65 years of age or older, as recommended by the ACIP, the incidence and severity of side effects has decreased substantially; however, particularly for older individuals, it is undesirable to administer amantadine over the several weeks required to prevent possible spread or reintroduction of influenza A viruses once the first evidence for an outbreak is detected, if the outbreak is actually due to influenza B or another respiratory pathogen.

The ability to rapidly diagnose influenza A infections would provide greater confidence in the use of amantadine for early treatment and prophylaxis of such cases, particularly when both type A and B influenza viruses are circulating. Nasopharyngeal specimens properly collected from residents and/or staff members within the first 1-3 days of illness before administration of amantadine can be tested using fluorescent microscopy and recently developed monclonal antibody reagents (3,4) to determine within 1 day whether or not influenza type A viruses are responsible for the outbreak. An alternative strategy would be to administer amantadine for 3 days to high-risk patients of an institution when an outbreak is beginning, and at the same time, obtain rapid virus culture confirmation by detecting antigen synthesized within 72 hours of inoculation of cell culture (5). In such a case, amantadine could be discontinued if either the outbreak continued to spread to amantadine-treated individuals and/or the laboratory diagnosis identified influenza B rather than influenza A viruses. Confirmation of influenza A infection would justify continued use of amantadine until risk of infection was over. Influenza A- and B-specific reagents for rapid virus typing have been distributed by CDC to all state health departments and other collaborating laboratories before the influenza season, although not all such laboratories may have established the diagnostic procedures referred to above.

References

  1. CDC. Update: influenza activity--United States, worldwide. MMWR 1986;35:28-9.

  2. ACIP. Prevention and control of influenza. MMWR 1985;34:261-8, 273-5.

  3. Gardner PS, McQuillin J. Rapid virus diagnosis. Application of immunfluorescence. 2nd ed. London: Butterworth & Co., 1980.

  4. McQuillin J, Madeley CR, Kendal AP. Monoclonal antibodies for the rapid diagnosis of influenza A and B virus infections by immunofluorescence. Lancet 1985;II:911-4.

  5. Walls HH, Harmon MW, Slagle JJ, et al. Characterization and evaluation of monoclonal antibodies developed for typing influenza A and influenza B viruses. J Clin Micro 1986 (in press). *Fever of 37.7 C (100 F) or higher and one or more respiratory symptoms. Approximately 20% of the 100 staff also had febrile respiratory illnesses slightly before or during the outbreak among residents. **Cases reported by those members of the American Academy of Family Physicians Research Panel who serve as sentinel physicians for influenza.

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