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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:

  1. 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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