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Epidemiologic Notes and Reports Outbreaks of Influenza among Nursing Home Residents -- Connecticut, United States

From January to April 1985, influenza viruses related to A/Philippines/2/82(H3N2) caused widespread or regional outbreaks in 37 states. In addition, the percentage of deaths attributed to pneumonia and influenza reported from 121 U.S. cities was the highest since 1976 (1). Outbreaks in nursing homes are often reported to CDC when influenza viruses circulate. Following are descriptions of investigations of influenza-like illness* in four Connecticut nursing homes and a summary of similar outbreak investigations reported by other states to CDC. CONNECTICUT

In February and March 1985, three separate outbreaks of influenza-like illness among nursing home residents were investigated by the Connecticut Department of Health Services and the Department of Epidemiology and Public Health, Yale University School of Medicine. Influenza type A(H3N2) appears to have caused all three outbreaks. Investigators found that, in each outbreak, residents who had recently received currently recommended influenza vaccine were just as likely as unvaccinated residents to become ill.

Outbreak 1. Nineteen residents of a skilled-care nursing facility had influenza-like illnesses. Ages ranged from 65 years to 94 years (median 84 years). Six of seven ill persons had fourfold or greater rises in hemagglutination-inhibition (HI) antibody against influenza A(H3N2) viruses but no comparable rises against other respiratory pathogens. Residents of only one floor of the facility became ill. On the affected floor, the attack rate was 25% (19/75); the rate was 26% (15/57) for vaccinated persons; 19% (3/16) for unvaccinated persons; and 50% (1/2) for residents whose vaccination status was unknown. None of these differences were statistically significant (p

0.05).

Outbreak 2. Twenty-six residents of a skilled-care nursing facility had influenza-like illnesses. Ages ranged from 33 years to 95 years (median 83 years). One of 14 throat swabs collected from ill residents yielded influenza A(H3N2) virus similar to A/Philippines/2/82. All six ill residents from whom serum specimens were obtained had fourfold or greater rises in HI antibody against influenza A(H3N2). The overall attack rate was 31% (26/85); the rate was 40% (12/30) for vaccinated persons and 25% (14/55) for unvaccinated persons (p

0.05). Vaccinated persons did not differ from unvaccinated persons in terms of age, sex, or level of needed care. After 41 (66%) of the remaining 62 well residents were started on amantadine hydrochloride prophylaxis (100 mg/day), only one, a resident who had not received amantadine, became ill.

Outbreak 3. One hundred eleven residents of a large multiple level-of-care facility had influenza-like illnesses. Ages ranged from 64 years to 104 years (median 85 years). One of six throat swab specimens yielded influenza A(H3N2) virus similar to A/Philippines/2/82. Fourteen of 18 ill residents from whom paired sera were obtained had fourfold or greater rises in antibody against influenza A(H3N2). The overall attack rate was 23% (111/489); the rate was 22% (75/336) for vaccinated persons; 20% (25/128) for unvaccinated persons; and 44% (11/25) for residents whose vaccination status were unknown (p

0.05). After the widespread institution of amantadine hydrochloride prophylaxis (100 mg/day) for residents and staff members, three additional cases were identified among residents on amantadine.

Ten influenza-related deaths were reported from all three nursing homes. Because of small numbers, statistically significant differences between vaccinated and unvaccinated influenza patients were not detected for length of illness, frequency of hospitalization, development of pneumonia, or risk of death.

Outbreak 4. A fourth influenza A(H3N2) outbreak in Connecticut was investigated by local personnel. Fourteen (23%) of 60 nursing home residents requiring intermediate care were affected, including 10 (20%) of 49 vaccinated persons and four (36%) of 11 unvaccinated persons (p

0.05). One influenza-related death was reported. ELSEWHERE IN THE UNITED STATES

To obtain additional data on the occurrence of influenza in nursing homes and to further evaluate the performance of the currently recommended influenza vaccine, CDC contacted officials in 24 state health departments during late March and early April. The 24 states were selected from all regions of the United States and were among those that had reported widespread or regional influenza activity for at least 2 consecutive weeks since December 1984.

Ninety outbreaks of influenza-like illness in nursing homes were reported through active or passive surveillance systems between December 1984 and April 1985. Fifty-three (59%) of these were investigated; influenza viruses related to A/Philippines/2/82(H3N2) were isolated from clinical specimens obtained in 27 (51%) of these homes, while the etiology of the remaining outbreaks could not be determined.

Vaccine efficacy estimates were available for nine outbreaks investigated by state and local health department personnel or university-based investigators in Georgia, Maryland, Minnesota, Pennsylvania, and Wyoming. Two hundred sixty-nine (25%) of 1,068 residents in these homes were affected overall; at least 26 (10%) of affected residents developed pneumonia, and 11 (4%) died. Attack rates in individual homes ranged from 13% to 49% (median 35%) and were often higher for unvaccinated residents (Table 1). Amantadine prophylaxis (100 mg/day) was initiated for all asymptomatic residents in three of the homes soon after the outbreaks became apparent, and no additional cases were identified. Reported by H Araneta, M Elcock, J Greene, M Greene, D Jacobson, R Kohn, C Motes, P Renzullo, A Ries, W Quinn, MPH, J Jekel, MD, Dept of Epidemiology and Public Health, Yale University School of Medicine, New Haven, M Markowski, Laboratory Div, JL Hadler, MD, State Epidemiologist, Connecticut Dept of Health Svcs; K Au, MD, J Burton, MD, Baltimore, D Dwyer, MD, E Cho, D Glasser, MD, Baltimore City Health Dept, F Lin, MD, JM Joseph, PhD, State Laboratory Director, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene; G Meiklejohn, MD, University of Colorado Health Sciences Center; H Crawford, MD, State Epidemiologist, Wyoming Dept of Health and Social Svcs; M Yates, M Rogers, MD, D Rimland, MD, Atlanta, RK Sikes, DVM, State Epidemiologist, Georgia Dept of Human Resources; C Pieper, C Snyder, Ramsey County Health Dept, L Stensland, Jackson County Health Dept, J Braun, MS, D Steipan, MS, CD Morse, DrPH, State Laboratory, M Osterholm, PhD, State Epidemiologist, Minnesota Dept of Health; L Budnick, MD, R Sharrar, MD, S Shapiro, MD, Philadelphia Dept of Public Health, M Dorman, T Zaborsky, D Gensemer, R Berman, MS, B Kleger, PhD, V Pidcoe, DrPH, State Laboratory, E Witte, VMD, State Epidemiologist, Pennsylvania State Dept of Health; Participating state epidemiologists and laboratory directors; Div of Field Svcs, Epidemiology Program Office, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, Office of the Director, CDC.

Editorial Note

Editorial Note: The results of the above vaccine efficacy studies should be interpreted cautiously because they were based on passively reported outbreaks that may not be representative of nursing homes in general and because few cases were laboratory confirmed. The results of these studies are consistent with those reported previously (2-12), most of which suggest that the efficacy of influenza vaccine in reducing the incidence of illness is often lower for nursing home residents than for younger, healthier populations. The reasons for this phenomenon probably include an age-related decline in immune response and high frequency of exposure and ease of transmission once the virus is introduced into the closed, relatively crowded setting (3). In addition, for reasons that are not well understood, influenza vaccine efficacy can vary from home to home. In a recent study of influenza-like illness among nursing home residents in Genesee County, Michigan (2), attack rates were similar for vaccinated and unvaccinated residents in six of the 13 homes studied, including three of the seven homes with outbreaks. Vaccination, however, was associated with a significant reduction in illness when the 1,476 residents were considered together.

Since complications following influenza virus infections account for the greatest impact on elderly patients in terms of both health and health-care costs, it is also important to evaluate the efficacy of influenza vaccine in reducing the severity of illness. Studies of elderly patients have consistently demonstrated a significant association between vaccination and reductions in the length of illness (9-11), the necessity for hospitalization (2,10), the development of pneumonia (2,10,13), and subsequent death (2,10,12,13). Furthermore, vaccination rates in individual nursing homes in the range of 70%-80%--a target recently proposed by the Immunization Practices Advisory Committee (ACIP) (14)--have also been shown to reduce the risk of outbreaks through the induction of herd immunity (15), which can further minimize the risk of severe influenza-related complications.

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