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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 57:M629-M635 (2002)
© 2002 The Gerontological Society of America

Hospitalizations and Deaths Due to Respiratory Illnesses During Influenza Seasons

A Comparison of Community Residents, Senior Housing Residents, and Nursing Home Residents

Verena H. Meneca, Leonard MacWilliama and Fred Y. Aokib

a Department of Community Health Sciences and Manitoba Centre for Health Policy, The University of Manitoba, Winnipeg, Canada
b Department of Medicine, The University of Manitoba, Winnipeg, Canada

Verena H. Menec, Dept. of Community Health Sciences, University of Manitoba, Winnipeg MB R3E 0W3, Canada E-mail: vmenec{at}cpe.umanitoba.ca.


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
Background. Although research indicates that influenza is a major cause of morbidity and mortality among older adults, few studies have tried to identify which seniors are particularly at risk of experiencing complications of influenza. The purpose of this study was to compare hospitalizations and deaths due to respiratory illnesses during influenza seasons among seniors (aged 65+) living in the community, senior residences (apartments reserved for seniors), and nursing homes.

Methods. Using administrative data, all hospital admissions and deaths due to respiratory illnesses (pneumonia and influenza, chronic lung disease, and acute respiratory diseases) were identified for all individuals aged 65 and older living in Winnipeg, Canada (approximately 88,000 individuals) during four influenza seasons (1995–1996 to 1998–1999).

Results. Hospitalization and death rates for respiratory illnesses increased significantly during influenza seasons, compared to fall periods (e.g., 42.7 vs 25.2 hospitalizations per 1000 population aged 80 and older). Moreover, hospitalization rates for pneumonia and influenza, chronic lung disease, and acute respiratory diseases were higher among individuals living in senior residences (42.5 per 1000 for all respiratory illnesses combined) than their counterparts living in the community (22.8 per 1000). Furthermore, deaths due to pneumonia and influenza and chronic lung disease were higher among senior housing residents (4.2 per 1000) than community residents (2.6 per 1000) and were particularly high among nursing home residents (52.1 per 1000).

Conclusions. Individuals living in seniors residences are at increased risk of being hospitalized for and dying of respiratory illnesses during influenza seasons. Given that influenza vaccination is currently the best method to reduce influenza-associated illnesses among seniors, this suggests that influenza vaccination strategies should be targeted at this population.

INFLUENZA is an important cause of morbidity and mortality. In Canada, 70,000 to 75,000 hospitalizations and approximately 6700 deaths each year are attributed to influenza and pneumonia (1). Influenza and pneumonia together are the sixth leading cause of death in Canada (2). The complications of influenza are primarily respiratory in nature and include pneumonia, acute respiratory diseases, and exacerbation of underlying medical conditions, such as chronic lung disease (3)(4)(5)(6)(7)(8)(9). Risk factors for complications of influenza are age and preexisting disease (3)(4)(5)(6)(7)(8)(9)(10)(11), with 80% to 90% of influenza-associated deaths occurring among people aged 65 and older (3)(4).

Influenza vaccination is currently the best method to attenuate the impact of influenza and reduce the risk of hospitalization and death among seniors aged 65 and older who live in the community, as well as among nursing home residents (9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Influenza vaccination is therefore recommended for all individuals aged 65 and older in most Western countries (19). Within Canada's universal health care system, influenza vaccination is provided free of charge to this target group (20). Canadian guidelines also specifically identify nursing home residents (of any age) as candidates of publicly-funded immunization programs (20). Despite its proven effectiveness, however, vaccination coverage is still quite low in Canada among noninstitutionalized seniors, ranging from 30% to 60% (21)(22)(23)(24). Better coverage (80% on average) has been attained in nursing homes because of concerted efforts to vaccinate this target group (25).

From a public health perspective, identifying individuals who are at risk and can easily be targeted for influenza vaccination campaigns is important. Although underlying medical conditions, such as chronic lung and heart disease, increase the risk of influenza-related complications (11), individuals suffering from chronic diseases may not be easily reached, unless they visit their physician during influenza vaccination seasons. One group of seniors that could potentially be readily identified and targeted for influenza vaccination campaigns is those living in senior residences—apartments reserved for seniors who do not require nursing care but do require some assistance, such as the provision of meals.

Few studies have compared the impact of influenza on seniors living in different types of housing. Research indicates that influenza-attributable deaths are particularly high among nursing home residents as compared to seniors living in the community (26), presumably because of the presence of underlying disease as well as the increased likelihood of rapid person-to-person spreading of influenza viruses. There is a paucity of research, however, on the impact of influenza on individuals living in senior residences. Living in senior residences represents a step on a continuum ranging from living independently in the community to requiring care in a nursing home (27)(28). Senior housing residents would therefore tend to have more chronic medical conditions than their counterparts living in the community. Moreover, congregate living increases the likelihood of the spread of respiratory viruses. Compared to their counterparts living in the community, senior housing residents might consequently be more susceptible to influenza-related complications.

In sum, the purpose of the present study was to examine whether senior housing residents are at greater risk of influenza-related respiratory illnesses during influenza seasons than their counterparts in the community. Specifically, we compared hospitalizations and deaths due to respiratory conditions over four influenza seasons among seniors (aged 65+) living in the community, in senior residences, and in nursing homes.


   Methods
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 Methods
Results
 Discussion
 References
 
Study Population and Data Sources
We examined hospital admissions for and deaths due to respiratory conditions among all seniors aged 65 and older (about 88,000 individuals) living in Winnipeg. With its approximately 650,000 residents, Winnipeg is the largest city in the province of Manitoba. Hospitalizations were identified from hospital discharge abstracts. Hospital use is free within Canada's universal health care insurance system, with all hospitalizations recorded for administrative purposes. The database has been used extensively for research and has been found to be of high quality in terms of completeness, validity, and reliability (29)(30). Deaths were determined from data obtained from the Office of Vital Statistics. These data, therefore, provide complete records of deaths in the province. Hospital admission and mortality rates were examined over 4 years (1995–1996 to 1998–1999).

Patient Characteristics
Age.-- Three age groups were created: 65–74, 75–79, and 80+ years old to differentiate between young-old, old-old, and oldest-old seniors. These age groups constituted about 53%, 21%, and 26% of the senior population, respectively.

Location of residence.-- Senior residences are apartment blocks specifically reserved for seniors who do not require nursing care beyond that provided through home care. Meals are provided in some senior residences. Senior residences were identified by means of a senior housing directory that provided a postal code for each senior residence in Winnipeg. Using postal code information contained in our administrative data (street addresses are not available in the dataset), we identified individuals living at these postal codes. Senior residences that shared postal codes with other (nonsenior residence) addresses had to be excluded, as we could not be sure where people lived. Overall, 111 of 130 (85%) senior residences listed in the senior housing directory were included in the present study. Thus, a small proportion of seniors who lived in a senior residence were misclassified as living in the community (<1% of community residents).

Nursing home residents were identified from administrative nursing home files. Access to nursing homes in Manitoba occurs on the basis of a standardized assessment based solely on need. Nursing home care is publicly insured (subject to a copayment assessed based on income). Community residents were defined as those individuals aged 65 and older who lived neither in a nursing home nor in a senior residence.

In 1998, 74,844 seniors (85%) lived in the community, 8723 (9.9%) lived in senior residences, and 4517 (5.1%) lived in nursing homes.

Comorbidity.-- The Refined Diagnostic Related Group classification system was used to examine whether community, senior housing, and nursing home residents who were hospitalized for respiratory conditions differed in terms of their level of comorbidity and complications. The system uses secondary diagnoses to classify cases into subgroups based on the presence or absence of substantial comorbidity or complications (31)(32).

Influenza Seasons and Comparison Period
Influenza seasons were defined as the weeks in each study year during which at least two positive tests for influenza A or B were obtained for Winnipeg residents at the provincial laboratory where all viral testing is conducted. Given this definition, influenza seasons lasted on average 15.3 weeks (range: 8 to 26 weeks). Influenza A viruses predominated in all 4 study years (33)(34)(35)(36).

Fall comparison periods were defined for each study year as a 3-month period ending prior to the influenza seasons (August to October).

Outcome Measures
Hospital admissions for respiratory conditions were examined for all of Winnipeg's acute care hospitals. They were identified among emergent/urgent medical patients (patients admitted through emergency), with medical cases identified using the Diagnostic Related Group classification system and emergent/urgent cases classified based on the admission status reported on the hospital discharge abstract. Among these emergent/urgent medical cases, patients were then identified who were admitted for respiratory conditions, using the most responsible diagnosis (the diagnosis that, upon discharge, was deemed most responsible for the patient's hospital stay). Deaths and cause of death were derived from Vital Statistics data for all Winnipeg seniors.

Diagnostic codes for respiratory conditions were chosen that have been shown to be complications of influenza in previous research (3)(4)(5)(6)(7)(8)(9)(13). They included: pneumonia and influenza (ICD-9-CM codes 480–487), chronic lung disease (codes 490–496), and acute respiratory diseases (codes 460–466).

Analytic Approach
Hospital admission and mortality rates for respiratory conditions were determined for both influenza seasons and fall periods, and 95% confidence intervals were calculated using methods developed by Carriere and Roos (37). To allow meaningful comparisons between the influenza seasons and fall periods, all rates (and descriptive statistics) were annualized by, for example, multiplying hospital admissions during the 61 weeks of influenza season by 0.852. Age-specific crude rates (per 1000 age-specific population) were calculated for each of the three age groups (65–74,75–79, 80+). Rates (per 1000 population) for the different types of housing were age-gender standardized to the 1998 population aged 65 and older (using the direct method), to control for the different age and gender distributions among community, senior housing, and nursing home residents.

Two general comparisons were made: (i) hospitalization and death rates during the influenza seasons were compared to those during the fall periods, and (ii) hospitalization and death rates were compared among the three different locations of residence. The rate of a particular group that is outside the confidence interval of a given comparison group differs in a statistically significant way from the comparison group ( p < .05).


   Results
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Discussion
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Hospital Admissions
Table 1 provides descriptive information on the characteristics of seniors in the different types of residences who were hospitalized for respiratory illnesses. Evident are the gender and age differences across the different types of residence. Compared to seniors living in the community, more women than men were hospitalized among nursing home residents and senior housing residents ({chi}2 = 19.6, p < .0001 for the influenza season). Moreover, nursing home and senior housing residents hospitalized for respiratory conditions were older than community residents ({chi}2 = 139.4, p < .0001). Community residents, senior housing residents, and nursing home residents did not differ in terms of their level of comorbidity and complications.


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  		Table 1. Characteristics of Patients Hospitalized for Respiratory Conditions, 1995–1996 to 1998–1999

 
Table 2 shows a breakdown of hospital admissions for respiratory conditions by gender, age group, and location of residence. Individuals aged 80 and older constituted the largest proportion of admissions for respiratory conditions in both the influenza seasons and fall periods across all study years, followed by persons aged 65–74 and seniors aged 75–79. Most admissions for respiratory conditions involved individuals living in the community—74.5% during influenza seasons, compared to 17.6% for seniors living in senior residences and 7.9% for nursing home residents. This distribution reflects the fact that most seniors indeed live in the community. As noted above, in 1998, 85% of all individuals aged 65 and older in Winnipeg lived in the community, 9.9% lived in senior residences, and 5.1% lived in nursing homes.


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  		Table 2. Percentage (Number) of Hospital Admissions for Respiratory Conditions, 1995–1996 to 1998–1999

 
Overall, 2216 admissions for respiratory conditions (annualized) occurred during the influenza seasons, as compared to 1387 during fall periods (46.3% of admissions involved pneumonia and influenza, 50.1% chronic lung disease, and 3.6% acute respiratory diseases).

Table 3 shows that admission rates (per 1000 population) were significantly higher ( p < .05) during influenza seasons than fall periods for all age groups for pneumonia and influenza, chronic lung disease, and acute respiratory diseases, although rates for acute respiratory diseases were low. Furthermore, admission rates were considerably higher among individuals aged 80 and older than among persons aged 75–79, who had, in turn, higher rates of admission than the 65–74-year-olds (during both the influenza seasons and the fall periods).


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  		Table 3. Annualized Hospital Admission Rates (per 1000 Population) for Respiratory Conditions, 1995–1996 to 1998–1999

 
Age-gender standardized rates during the influenza seasons also differed significantly from those during the fall periods across all types of housing for all three diagnostic categories. Moreover, rates were significantly higher for seniors living in senior residences than among their counterparts living in the community for pneumonia and influenza, chronic lung disease, and acute respiratory diseases (see Fig. 1). For example, the annualized hospitalization rate for senior housing residents during influenza seasons was 42.5 (per 1000 population), compared to 22.8 for community residents. Admission rates among nursing home residents were higher than among community residents for pneumonia and influenza (both during the influenza season and fall period), but were lower for chronic lung disease. For acute respiratory diseases, nursing home residents differed from community residents during influenza seasons, but not fall periods.



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  		Figure 1. Age-gender adjusted annualized hospital admission rates (per 1000 population) for respiratory conditions, 1995–1996 to 1998–1999.

 
Deaths
Descriptive statistics are provided in Table 4 . Most deaths due to respiratory conditions were among individuals aged 80 and older (68.4% during the influenza seasons), and a large proportion occurred among nursing home residents (50.3% during the influenza seasons). Overall, 459 deaths due to respiratory illnesses (annualized) occurred during influenza seasons (53.2% of those due to pneumonia and influenza, 46.8% due to chronic lung disease), compared to 286 during fall periods.


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  		Table 4. Percentage (Number) of Deaths Due to Respiratory Conditions, 1995–1996 to 1998–1999

 
Increased mortality rates for pneumonia and influenza and chronic lung disease during the influenza seasons, compared to fall periods ( p < .05), emerged for all age groups (except for deaths due to pneumonia and influenza among the 65–74-year-olds) and across most locations of residence (see Table 5 ). Mortality rates were higher among senior housing residents than seniors living in the community. They were substantially higher among nursing home residents compared to their counterparts in the community (both during the influenza season and the fall period).


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  		Table 5. Annualized Mortality Rates (per 1000 Population) for Respiratory Conditions, 1995–1996 to 1998–1999

 

   Discussion
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 Discussion
References
 
Consistent with previous research, hospitalizations and deaths due to pneumonia and influenza and chronic lung disease increased significantly during influenza seasons, particularly among the oldest-old (8). Hospitalizations for acute respiratory diseases also increased during the influenza seasons; however, they constituted only a small percentage of admissions for respiratory conditions (<5%) in our senior population.

Hospital admission rates were higher for seniors living in senior residences than their counterparts living in the community for pneumonia and influenza, chronic lung disease, and acute respiratory diseases. Indeed, rates of hospitalization for chronic lung disease were higher among senior housing residents than nursing home residents. Although deaths due to pneumonia and influenza and chronic lung disease were also elevated for senior housing residents, compared to community residents, rates were relatively small. Only 8% of deaths due to respiratory illnesses involved senior housing residents.

It is important to address several limitations of the present study at this point. First, although we know that influenza A (and to a much lesser extent influenza B) viruses were circulating during the periods that we identified as influenza seasons, increased hospital and mortality rates during these time periods may, in part, have been caused by other respiratory viruses, such as parainfluenza virus, respiratory syncytial virus, and adenovirus (38)(39). Given that the time periods during which these viruses are active typically overlap with influenza seasons, it is difficult to disentangle the relative impact of each virus.

Second, it was not possible to identify seniors' influenza vaccination status, as no systematic vaccination records were kept for adults in the province of Manitoba during the study years. Thus, it was not possible to examine hospitalizations and deaths for those vaccinated versus those not vaccinated. Third, we included only respiratory conditions in the present study, although research indicates that influenza can also exacerbate underlying chronic heart conditions (7)(8)(9)(13). The present study therefore likely underestimates the burden of serious morbidity during influenza seasons.

Previous research indicates that influenza vaccination is the best method to reduce hospitalizations and deaths due to influenza-associated illnesses during influenza seasons among seniors, including individuals in nursing homes (9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Although Canadian guidelines recommend that all seniors aged 65 and older be vaccinated for influenza, with influenza vaccination provided free of charge, vaccination coverage has been low among noninstitutionalized seniors (about 40% to 50% in Manitoba) (21)(22). Thus, the relatively high rates of hospital admissions and deaths during influenza seasons among individuals living in senior residences, compared to their counterparts living in the community, found in the present study are unlikely to be due to differences in influenza vaccination rates. The findings suggest, therefore, that senior housing residents should be a priority for influenza vaccination campaigns.

Individuals living in senior residences are a readily identifiable population that could presumably be easily reached with mass influenza vaccination strategies, such as on-site clinics, with the potential benefits for reducing serious morbidity being substantial. Canadian guidelines do not currently specifically identify individuals in senior housing as a target group for influenza vaccination, although it is recommended that noninstitutionalized individuals aged 65 and older should be offered immunization by public health units in a variety of settings, including senior citizen centers and residences (1). The present findings clearly support this recommendation.

Similar to previous research (26), the present study also shows that hospital admissions and deaths due to pneumonia and influenza and chronic lung disease were higher among nursing home residents than individuals aged 65 and older living in the community. Given that influenza vaccination coverage is already high in nursing homes in Manitoba, this may reflect reduced vaccine efficacy in a population with a high prevalence of preexisting health problems, which would be consistent with previous research (40).

In sum, the present study adds to the literature by specifically focusing on individuals aged 65 and older living in senior residences and showing that they are at higher risk of being hospitalized for and dying of respiratory conditions during influenza seasons than their counterparts living in the community. Influenza vaccination campaigns targeted at this high-risk group could potentially reduce the burden of illness substantially.


   Acknowledgments
 
V. Menec holds a New Investigator Career award from the Canadian Institutes of Health Research. We thank the Health Information Services, Manitoba Health, and the Office of Vital Statistics in the Agency of Consumer and Corporate Affairs for the provision of data.

Received January 3, 2002

Accepted March 11, 2002


   References
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 References
 

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