A Rhinovirus Outbreak among Residents of a Long-Term Care Facility

The rhinoviruses are a common cause of acute respiratory illness and are estimated to cause approximately one third of all common colds [1]. Among persons of all ages, rhinovirus infection typically produces a mild upper respiratory illness consisting of coryza and cough [2]. The rate of infection is highest among children and decreases throughout adulthood, presumably because of immunity induced by cumulative exposure to different serotypes and less frequent close contact with infected persons [1, 3]. Because more than 100 rhinovirus serotypes exist and immunity is not absolute, persons may have multiple infections during a lifetime [4]. Although infection is usually benign, it can cause serious lower respiratory illness in certain populations. For example, in hospital-based studies of infants with bronchiolitis, respiratory distress, and pneumonia, rhinovirus has been causally implicated in a minority of illnesses [4-6]. Prospective studies of children and adults with asthma have shown that various rhinovirus serotypes are common precipitants of asthma attacks [7-9]. Similarly, rhinovirus has been cultured from 14% to 23% of adults with chronic obstructive pulmonary disease having symptomatic exacerbations [10, 11]. Despite extensive investigation in younger age groups, few studies have been done of rhinovirus infection in elderly persons, particularly those residing in long-term care facilities. Although outbreaks have been described among children and young adults, prospective studies in nursing homes have identified rhinovirus in only a minority of ill residents, and large outbreaks have not been described [2, 4, 12, 13]. Similarly, little information is available about the clinical manifestations of rhinovirus infection in elderly persons. A large, community-based study of persons with rhinovirus infection noted that those older than 40 years of age were more likely than younger adults to have lower respiratory symptoms (65% compared with 34%) and a longer duration of illness (20 days compared with 13 days), which suggests that infection may be more severe in older persons [1]. However, only 17 isolates were obtained from persons older than 40 years of age, and the age distribution of these persons was not reported. In contrast, Falsey and coworkers [13] studied 14 nursing home residents infected with rhinovirus and noted that the associated illnesses were not serious and that a minority of persons had symptoms or examination findings suggestive of lower respiratory tract involvement. In this report, we describe an outbreak of culture-proven rhinovirus illnesses that occurred in the late summer of 1993 among residents of a large, rural Wisconsin nursing home. This home is the site of an ongoing, 5-year, influenza-prevention study. In mid-August 1993, in response to an increase in the number of respiratory illnesses in this facility and the early onset of influenza noted in the southern United States [14], viral cultures were done to exclude influenza. These cultures yielded 33 rhinovirus isolates. Analysis of this outbreak showed that, contrary to its reputation for causing mild illness, rhinovirus may cause large outbreaks of clinically important respiratory illness among nursing home residents. Methods Study Sample The study sample resided in a 685-bed, long-term care facility for wartime veterans and their spouses. The facility is in rural Wisconsin and includes four residential buildings connected by underground tunnels. The four buildings have a total of 13 residential floors, each housing 50 to 60 residents. Approximately one half of the beds are allocated for intermediate care and one half for skilled care. A 2-story recreational building allows residents from different buildings to congregate and is connected to the residential buildings by underground tunnels. Surveillance During the winter season, active surveillance for respiratory illness is done at the facility as part of an ongoing influenza-prevention study. During the rest of the year, including the period of this study, the nursing staff conducts passive surveillance for respiratory illness using a daily illness reporting system. This system identifies and tracks any resident with fever (oral temperature more than equals 100.0 F) or other symptoms indicating possible viral infection; ill persons are identified by self-report or by the nursing staff during routine encounters. During the third week of August 1993, an increase in the number of respiratory illnesses was noted among persons residing in a building (building C) in which persons with pulmonary disease were housed. In response, the nursing staff were asked to report all new respiratory illnesses to the nurses participating in the influenza study. These nurses recorded the date of illness onset and obtained respiratory viral cultures. Virus Culture After verbal consent was obtained, viral cultures were taken from ill persons but not from well persons. Cultures were obtained by swabbing the nasopharynx (using rayon-tipped flexible aluminum swabs) and throat (using dacron-tipped plastic swabs) and placing the swabs into a virus-transport medium (veal broth with gentamicin, penicillin, streptomycin, and amphotericin). Specimens were cooled to 4 C within 1 hour of sampling and were inoculated within 24 hours into primary rhesus monkey kidney, HEp-2, and Wi-38 tube-cell cultures and Madin Darby canine kidney 24-well plate cultures. This panel of cell cultures enables detection of all common cultivable respiratory viruses. Tube-cell cultures were incubated at 33 C on a roller apparatus, and 24-well plate cultures were incubated at 35 C. Cells were examined for cytopathic effect and hemadsorption. Rhinovirus was confirmed by growth with characteristic cytopathic effect in Wi-38 cells and by acid lability. Negative cultures were held for 2 weeks before they were discarded. Epidemiology The outbreak was defined as the interval between the onset of symptoms in the first and last persons to yield rhinovirus isolates (14 August to 2 September 1993). The daily illness reports for the entire facility were reviewed for the period during and surrounding the outbreak to identify all new respiratory illness. A respiratory illness was defined as the presence of at least one new respiratory symptom not accounted for by another disease process; the presence of fever was not required. A rhinovirus infection was defined as a respiratory illness associated with a culture isolate of rhinovirus. The incidence of respiratory illness was calculated for each residential building and floor. The room locations of persons with rhinovirus infection were determined so that the geography of the outbreak and the risk for developing illness among close contacts could be studied. Rhinovirus was isolated from one person during three separate symptomatic episodes; the first episode occurred during the outbreak and the other two in the ensuing 3 months. Information from the first illness only is included in the discussion of the outbreak. Information from all three illnesses is included in the clinical results. Medical Record Review After the outbreak, the medical records of persons from whom rhinovirus was isolated were reviewed. Age, sex, level of nursing care, duration of residence in the facility, underlying medical conditions, scheduled medications, and pulmonary examinations done by the residents' physicians composed the pre-illness database. Underlying medical conditions were obtained from a clinical problem list generated by each resident's physician. Illness data were abstracted from the medical records and recorded on a standard form; these data included the type and duration of symptoms, concurrent pulmonary examinations, oral temperatures, physician telephone calls and visits, results of chest radiographs, laboratory and sputum test results, and the use of oxygen, medication for symptom relief, and antibiotics. Symptoms were determined to be illness-related if they were new or worse during the illness; symptoms included upper respiratory (nasal or sinus congestion, coryza, sore throat, or cough), lower respiratory (productive cough, hoarseness, or dyspnea), gastrointestinal (anorexia, nausea, vomiting, or diarrhea), and systemic symptoms (malaise, fatigue, myalgia, sweating, or chilling). The duration of illness was defined as the interval between the first recorded symptom and either the time that residents returned to their usual activities or the time that the medical staff determined that the illness had resolved, whichever came first. Lungs were examined at the discretion of the medical personnel caring for the residents; examinations were done in 29 illnesses (by both the physician and staff nurses in 9 illnesses, by the physician only in 4 illnesses, and by the nurses only in 16 illnesses). Lung examination findings were attributed to rhinovirus if they were not present on any of the three most recent pre-illness pulmonary examinations done by the resident's physician. Data Analysis Categorical data were analyzed using the chi-square test or the Fisher exact test. Continuous data were analyzed using the Wilcoxon rank-sum test. The significance level was P < 0.05 (two-tailed) for all tests. Results The Outbreak: Number of Illnesses and Rhinovirus Isolates Figure 1 shows the outbreak, which includes the period between the onset of symptoms in the first and last persons whose cultures yielded rhinovirus (14 August to 2 September 1993). During the outbreak, each of 128 residents developed a new respiratory illness. Sixty-seven persons (52%) were cultured; 33 of the cultures (49%) yielded rhinovirus. No other respiratory virus was isolated from those persons cultured. The isolation of rhinovirus coincided with an increase in the number of respiratory illnesses facility-wide. After the outbreak, the number of respiratory illnesses decreased, and no further viruses were isolated. Figure 1. Outbreak curve for