Long-term care facilities.
Although RSV infection was reported in 18 hospitalized older adults in Sweden as early as 1967, it was not until several nursing home outbreaks were described in the late 1970s and early 1980s that RSV was appreciated as a serious pathogen in the elderly (
18,
55,
60,
123). Since that time, there have been seven reports of outbreaks and 11 prospective studies in long-term care facilities (LTCF) in which RSV was identified (Table
2) (
1,
8,
18,
39,
44,
60,
73,
90,
100,
120,
123,
133,
140,
147,
148,
155,
165,
179). Attack rates range widely, from 1 to 89%, and may depend upon the case definitions and diagnostic tests used. Prospective studies in which all respiratory infections were evaluated and RSV cases were defined as a positive culture or a greater than fourfold rise in antibody probably reflect the most accurate RSV infection rates. In these studies, rates of infection ranged from 2 to 12% (
1,
8,
44,
100,
140). Infection rates in institutionalized persons may also be variable because the outbreaks occur in closed populations and the virus is subject to nosocomial spread. During one season in Rochester, New York, two nursing homes were assessed for influenza and RSV; at one institution, influenza A was prevalent and RSV accounted for only 3% of illnesses, whereas at the other home, RSV was the dominant pathogen and caused 20% of the illnesses (
39).
Complication rates in previous reports have also been quite variable, with the incidence of pneumonia ranging between 0 and 55% and death rates of 0 to 53% (
100,
155,
165). Again, these marked differences in severity may be due in part to case definitions used in outbreak situations, but there may also be differences in strain virulence or the chronic medical conditions of residents. For example, in the report by Sorvillo, the attack rate for symptomatic RSV illness was high at 40%, and 55% of those ill had radiographically documented pneumonia (
165). This is in contrast to the study by Osterweil, in which pneumonia and death rates were 5 and 2%, respectively (
148). The true incidence of pneumonia in residents of LTCF may be underestimated because chest radiographs are not routinely obtained. Although rates of documented pneumonia can be variable, lower respiratory signs are common in most studies of RSV (
44,
60,
140).
Elderly persons who attend senior daycare programs also appear to be at increased risk for RSV infection. One study, which examined viral infections among staff and elderly participants of a daycare program, found RSV to be a common pathogen in both groups (
37). Over a 15-month period, 10% of 165 elderly and 5% of the 113 staff members developed respiratory infections caused by RSV. This agent was among the most commonly identified viruses, along with influenza A virus and coronaviruses. Of interest, children from a nearby center visited with elderly participants approximately once a week, although transmission of viruses was not evaluated specifically.
Although most of the current information on RSV in institutionalized persons involves elderly persons, there is one report of an RSV outbreak in a residential institution for mentally retarded young adults (
51). The attack rate was 50% and substantial morbidity was associated with illness. Of the 24 affected individuals, 42% wheezed, 17% were hospitalized, and a 19-year-old woman with multiple medical problems died. Both younger age and less time institutionalized were risk factors for infection with RSV.
In summary, RSV appears to be a predictable cause of wintertime respiratory illnesses in LTCF. Although rates vary from year to year and with individual institutions surveyed, a reasonable estimate is that RSV will infect 5 to 10% of residents per year, with rates of pneumonia and death of 10 to 20% and 2 to 5%, respectively.
Community-dwelling elderly.
The incidence and impact of RSV infection in older persons who live independently in the community have not been well studied. RSV is thought to be an underrecognized pathogen in older adults, based on case reports of RSV pneumonia, studies of adults with respiratory disease requiring hospitalization, and epidemiological studies from the United Kingdom. A review of RSV isolates in Scotland between 1971 and 1979 indicated that 4 to 18% occurred in adults ages 25 to 29 and 3 to 16% occurred in persons over age 60 (
7). An analysis of excess deaths and respiratory disease in England by Fleming and Cross showed that peaks of excess morbidity and mortality in persons over age 65 occurred when RSV activity was highest in the community, as judged from viral isolates recovered from children (
52). In most years, the peak of influenza activity occurred simultaneously with RSV, obscuring its effect. However, when the peaks in viral activity were temporally separated, the effect of RSV on excess morbidity and mortality was similar to that seen with influenza. In another analysis of the impact of influenza and RSV in the United Kingdom, Nicholson applied statistical modeling to 15 years of data and estimated that the impact of RSV was greater than that of influenza (
139).
In addition to the epidemiological evidence that RSV is a problem in adults, there are a number of reports of adults hospitalized with pneumonia. Many of the case reports involve adults with chronic medical conditions such as Wegener's granulomatosis, systemic lupus erythematosus, and renal failure (
136,
167,
193). However, some reports describe previously healthy adults whose only risk factor appeared to be advanced age (
114,
193). In one well-documented case, a 72-year-old woman living independently at home with no chronic cardiopulmonary or immunosuppressive diseases died of RSV pneumonia (
114).
The earliest large study which specifically sought RSV as a cause of lower respiratory tract disease in community-dwelling adults was performed by Fransen in Sweden from 1963 to 1966 (
55). Eighteen persons over age 55 with RSV were identified, and the highest rate of RSV infection was found in the ≥60-year-old group, in which 16 of 216 (7.4%) illnesses were due to RSV. In another Swedish study, RSV infections were identified serologically in 57 adult patients over a 10-year period (
178). The median age was 75 years, and the incidence of pneumonia was 63%. In two other studies which used viral culture alone for diagnosis, RSV was detected in 2 to 5% of patient samples (
109,
194). Two more recent, larger studies of hospitalized adults again show RSV to be a common pathogen (
27,
42). In a study of elderly persons in upstate New York admitted during three winters with acute cardiopulmonary conditions, RSV was identified in 10% of patients, compared to 13% with influenza (
42). The morbidity was substantial, with 18% of patients admitted to intensive care and 10% requiring ventilatory support, and 10% died. Although 44% had a discharge diagnosis of pneumonia, much of the RSV morbidity was associated with other diagnoses, including chronic obstructive pulmonary disease (COPD) exacerbation (19%) and congestive heart failure (20%). A recent study by Dowell et al., which was not limited to elderly adults, found RSV to be the third most common identifiable cause of pneumonia at 4.4% in 1,195 adults with community-acquired pneumonia (
27). This compared to
Streptococcus pneumoniae at 6.2% and influenza virus at 5.4%. Of the 57 RSV-infected patients, 32% were younger than 65 and 8 individuals were less than 40 years old. Surprisingly, the young adults were otherwise healthy. Lastly, a number of studies evaluating the etiology of community-acquired pneumonia have identified RSV with variable success (Table
3) (
27,
42,
54,
96,
121,
128,
159,
169,
178,
194). The variability in infection rates likely reflects the diagnostic tools used and seasons studied but may also reflect some differences in geographic distribution of the virus. A reasonable estimate using data from a number of studies during the past 30 years is that RSV accounts for 2 to 5% of pneumonias throughout the year and 5 to 15% during the winter.
Prospective studies, which evaluate the total burden of RSV disease in community-dwelling older persons, have yet to be done. A number of large surveillance studies of acute respiratory infection (ARI) show declining rates of infection with advancing age, yet the number of middle-aged and older adults studied was small (
132). Hodder et al. evaluated the rates of ARI but not specific pathogens in noninstitutionalized adults over age 65 (
99). The average incidence of ARI was 2.5 per 100 person-months and was significantly greater for those living in congregate settings (3.2) and those regularly caring for young children (3.0). Nicholson conducted the only prospective study of ARI in elderly persons in the community to date, which examined the frequency of specific viral pathogens (
141). RSV accounted for 3% of the 497 illnesses among 533 persons followed for two winter seasons. This compared to 7% identified as influenza and 52% due to rhinoviruses. A true comparison of the burden of disease from specific pathogens is not possible because very different diagnostic tools were used for each pathogen.