Feature Article
|
An Influenza Outbreak in an Immunized Nursing Home Population: Inadequate Host Response or Vaccine Failure? Objective:To describe an outbreak of influenza A in an immunized nursing home population.
Design: Observational cohort study.
Setting:Subjects include residents and staff members of a skilled nursing facility in Rochester, Minnesota, at the time of an influenza outbreak in November 1996.
Methods: Review of medical records, incident reports, and Minnesota State Health Department data.
Results: During a 5-day period, 27 of 62 residents (attack rate = 44%), and 16 of 67 staff members (attack rate = 24%) developed symptoms consistent with acute influenza infection. Influenza A was confirmed by throat culture in the index case and in three other initial cases. Ninety-five percent of residents and 72% of staff members with direct patient contact had been immunized 4ú8 weeks prior to the outbreak. Two symptomatic residents (5%) were hospitalized, and one nonhospitalized resident died (2.3% mortality). The viral strain isolated from the outbreak (A/Wuhan/H3N2) was antigenically identical to the one (A/Nanchang/H3N2) contained in the vaccine.
Conclusion: Annual influenza vaccination of nursing home residents and staff members, though advisable, does not afford complete protection from infection of nursing home residents or staff members. The higher attack rates among nursing home residents compared to staff members suggest that older nursing home residents may mount an inadequate host response to influenza vaccination or exposure. (Annals of Long-Term Care 1998;6[3]:72)
Introduction
Acute influenza infection is a significant cause of morbidity and mortality among nursing home residents, accounting for up to 40,000 deaths, as well as more than $1 billion in Medicare expenditures annually.1 Ninety percent of such deaths occur in the elderly. Consequently, it is recommended that nursing home residents and staff members be immunized annually. Institutional crowding, depressed immunity, and chronic medical illness in this population result in lower efficacy of vaccination and higher infection rates.2 A review of an outbreak in a well-immunized nursing home population was conducted to determine if vaccine failure occurred. In this study, researchers analyzed the literature and Minnesota State Health Department data to learn more about influenza infections and the efficacy of vaccinations in this population.
Methods
This study assessed a 1996 outbreak of influenza in a 62-bed, community-based skilled nursing facility in Rochester, Minnesota. Subjects were all residents of the facility (n = 62 [54 female; 8 male]), ranging in age from 77 to 101 years old (mean age, 87 ± 4 years), and staff members who had direct patient contact (n = 72), including aides, nurses, social workers, recreational and physical therapists, and meal servers.
Design
Prior to the flu season, nurses, aides, and other support staff members were trained to recognize signs and symptoms of influenza and to report cases as delineated in the facility infection control policy manual. Subjects were considered to have influenza if they met clinical criteria established by the Centers for Disease Control and Prevention3: (1) fever of at least 100°F orally, 101°F rectally, or 99°F by axilla; and (2) at least one respiratory sign or symptom of cough, sore throat, or runny/stuffy nose.
Detection and Treatment
The beginning of the outbreak was characterized by a 2-day period in which six symptomatic residents and three symptomatic staff members were reported (Figure). The medical director and attending physicians were notified, and the facility's influenza infection control action plan was activated. Pharyngeal swab cultures for influenza A and group A streptococci were first obtained for the index case and then for 11 of the subsequent cases. The Minnesota State Health Department was immediately notified, symptomatic residents were restricted to their rooms, and all group activities were suspended. Symptomatic staff members and all visitors were restricted from the facility. All symptomatic residents were treated with rimantidine, and influenza chemoprophylaxis was initiated for the remaining residents. The staff members were encouraged to seek treatment or prophylaxis from their physicians.
An ongoing log was kept of reported symptoms, culture results, hospitalizations, and deaths (Table I). In addition, the complete medical records of symptomatic residents were reviewed. Statewide data on influenza outbreaks in other skilled nursing facilities were obtained from the Minnesota State Health Department at the conclusion of the 1996ú1997 influenza season.
Results
During a 1-week period from November 29, 1996, to December 5, 1996, 43 of 134 subjects (32%) developed signs and symptoms fulfilling clinical criteria for acute influenza infection. Twenty-seven residents (44%) and 16 staff members (24%) were infected. Two residents (7.4%) were hospitalized, and one died (overall resident mortality rate, 2.3%). Ninety-five percent of residents and 72% of staff members with direct patient contact had been immunized at least 4ú8 weeks prior to the outbreak (between 10/5/96 and 10/28/96). Of those subjects who developed influenza, 96% of infected residents (26 out of 27) and 52% of infected staff members (9 out of 16) had been immunized (Table II).
The first symptomatic resident and 3 out of 11 additional residents (33% overall) had pharyngeal swab specimens in which influenza A/Wuhan (H3N2) was isolated. Group A streptococcus was not isolated from any of the cultures. The isolated strain was antigenically identical to A/Nanchang (H3N2) contained in the influenza vaccine.
Minnesota State Epidemiologic Data
During the 1996ú1997 influenza season, outbreaks were voluntarily reported in 31 of 440 nursing homes in Minnesota. Thirty-five percent of reported cases were confirmed by culture. The Wuhan strain was identified in 84% of 485 culture-confirmed cases. Influenza A of unknown strain was cultured from the remaining 16%. Hospitalization rate was 7.4% among symptomatic nursing home residents. The protection rate of influenza vaccine calculated by the state of Minnesota among immunized residents was 56% (Table III).
Discussion
This study assessed an outbreak of influenza A in a single skilled nursing facility in which the vaccination rate among residents and staff members was exceptionally high, and the viral strain causing infection was identical to one against which they had been immunized. It would appear that infection in this outbreak resulted either from a failure of host immune response or from a failure of the vaccine itself. Of note, during the same flu season (1996ú1997), there was a voluntary recall of influenza vaccine by one manufacturer because of concerns about possible decreased efficacy of one of the components. Although none of the subjects in the outbreak we describe received the recalled vaccine, this recall heightened our concern about the possibility of a vaccine failure.
Influenza continues to be a cause of significant morbidity and mortality among the elderly. Frail, chronically ill patients are at particularly high risk of adverse outcomes of infections, and influenza outbreaks within residential care facilities are commonplace.4,5 Consequently, annual vaccination of all nursing home residents and staff members is currently recommended by the Advisory Committee for Immunization Practices.3 Despite widespread vaccination, however, influenza outbreaks continue to occur in nursing homes. The risk of an outbreak in a long-term care environment is thought to be inversely proportional to the vaccination rate among residents.
Whereas vaccine failure cannot be completely ruled out in the outbreak described in this article, it appears that impaired host response is likely to have been a factor, as evidenced by a higher infection rate among elderly nursing home residents compared to younger nursing home staff members with a lower vaccination rate.
Although there is some debate about the efficacy of influenza vaccination in the elderly, several studies suggest that the risk of influenza infection among vaccinated individuals increases with age.2,6,7 In one randomized, prospective, placebo-controlled trial, vaccination of community-dwelling elderly conferred a protection rate of 43% to 68%, depending on the viral strain.2 These protection rates are significantly lower than those reported for younger individuals. Among institutionalized elderly, even lower protection rates (28% to 37%) have been reported.
Despite these low protection rates, however, vaccination of nursing home residents has been associated with a 79% reduction in mortality from influenza infection or secondary pneumonia (Table IV).6,8 Thus, there appears to be a cumulative benefit to annual vaccination. In a previous study, higher infection rates (5.1%) were seen in community-dwelling subjects who had never been vaccinated before, compared to subjects who had been vaccinated in the previous year against the same strain (0.9%).2 The statewide protection rate among Minnesota nursing home residents who were immunized during the 1996ú1997 influenza season was 56%. This higher protection rate is likely the result of improved infection control policies and procedures in nursing homes that have been implemented over the past decade.
The Medical Director's Role
Medical directors can and should play a key role in infection control in the nursing home. With regard to influenza in particular, it is recommended that the medical director annually review the facility's pertinent policies and procedures, and revise them as needed, to ensure that they are both appropriate and feasible. Because of the seasonal nature of influenza infection, an autumn in-service workshop given by the medical director can be useful in educating staff members about influenza and in encouraging vaccination of all staff members. The medical director may also be able to persuade the facility to provide immunizations (and if influenza occurs, antiviral treatment) to all staff members free of charge in an effort to further reduce the occurrence or contagiousness of influenza.
Conclusion
Influenza infection occurs in long-term care environments despite appropriate vaccination of elderly residents. The protective effect of influenza vaccination appears to decrease with advancing age. This is most likely attributable to elderly individuals' impaired host immune response. Nevertheless, annual vaccination continues to be recommended and may have a cumulative benefit. Vigilant surveillance and infection control policies and procedures in the nursing home may further reduce the spread of infection.
References
1. McBean M, Babish MSC, Warren JL. Impact and cost of influenza in the elderly. Arch Intern Med 1993;153:2105ú2111.
2. Advisory Committee on Immunization Practices. Prevention and Control of Influenza. Pt I: Vaccine Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 1993:42 (RR-6):1ú13.
3. Advisory Committee on Immunization Practices. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 1996;45:1ú24.
4. Govaert ME, Sprenger MJW. Immune response to influenza vaccination of elderly people: A randomized double-blind placebo controlled trial. Vaccine 1994;12:1185ú1189.
5. Patriarca PA, Weber JA. Efficacy of influenza vaccine in nursing homes: Reduction in illness and complication during an influenza A (H3N2) epidemic. JAMA l985;253:1136ú1139.
6. Eickhoff TC, Sherman IL, Serfling RE. Observations of excess mortality associated with epidemic influenza. JAMA 1961;176:776ú782.
7. Alling DW, Blackwell WC, Stuart-Harris CW. A study of excess mortality during influenza epidemics in the US: 1968ú1976. Am J Epidemiol l981; 113:30ú43.
8. Barker WH, Mullooly JP. Influenza vaccination of elderly persons: Reduction in pneumonia and influenza hospitalization and deaths. JAMA 1980; 244:2547ú2549.
About the Author
Dr. Kuhle is on the faculty at Mercy/Mayo Family Practice Residency in Des Moines, Iowa. Dr. Evans is an Assistant Professor, Internal Medicine Section, Ms. Bauman is a Geriatric Nurse Practitioner, and Dr. Poland is a Professor of Medicine, all at the Mayo Clinic in Rochester, Minnesota. Ms. Breese is a nurse at Madonna Towers Nursing Home in Rochester, Minnesota. Dr. Rodysill is a Staff Physician, Internal Medicine Department, at the Mayo Clinic and Medical Director at Madonna Towers Nursing Home. Address for correspondence: Carol L. Kuhle, Mercy/Mayo Family Practice Residency, 250 Laurel St, Des Moines, IA 50314. Annals of Long-Term Care - ISSN: 1524-7929 - Volume 6 - Issue 03 - March 1998 |