A Study of the Impact of Influenza on the Functional Status of Frail Older People

BACKGROUND: Excess hospitalization and death are well-known impacts of influenza on older people; however, little is known regarding the impact of influenza on functional status. We hypothesized that frail older people are at risk of functional decline as an outcome of influenza. OBJECTIVE: To measure the effect of acute influenza on the physical and mental status of older patients residing in nursing homes. METHODS: Our study was conducted in 6 nursing homes that participated in the Medicare Influenza Vaccine Demonstration and experienced laboratory-confirmed outbreaks of influenza in 1991 and 1992. A case-comparison design was used. One hundred sixteen of 131 residents who developed influenza-like illness and survived at least 4 months served as the case subjects; 127 of 132 residents without influenza-like illness who survived served as the comparison subjects. Measures of functional status 1 to 2 months before outbreak and 1 to 2 months and 3 to 4 months after outbreak were collected from medical records. Matched pairs analyses were conducted to ascertain changes in selected measures of functional status within each of the study groups. Wilcoxon signed rank tests for statistical significance were used. RESULTS: Among surviving case subjects and comparison subjects, 25% and 15.7%, respectively, experienced decline in at least 1 major function (P=.04). Case subjects experienced significant decline in independence in bathing, dressing, and mobility while comparison subjects experienced decline in mental status. CONCLUSIONS: Within the limitations of this study, influenza is observed to cause decline in major physical functions in more than 9% of survivors. Such disabling outcomes constitute an important new measure of impact of influenza on the frail elderly.