Effect of Influenza on Functional Decline

Objectives To examine the relationship between influenza and activity of daily living (ADL) decline and other clinical indicators in nursing home (NH) residents. Design Retrospective NH-aggregated longitudinal study. Setting Two thousand three hundred fifty-one NHs in 122 U.S. cities from 1999 to 2005. Participants Long-stay (>90 days) NH residents. Measurements Quarterly city-level influenza mortality and state-level influenza severity. Quarterly incidence of Minimum Data Setderived ADL decline (=4 points), weight loss, new or worsening pressure ulcers (PUs), and infections. Outcome variables chosen as clinical controls were antipsychotic use, restraint use, and persistent pain. Results City-level influenza mortality and state-level influenza severity were associated with higher rates of large (=4 points) ADL decline (mortality beta = 0.20, P < .001; severity beta = 0.18, P < .001), weight loss (beta = 0.19, P < .001; beta = 0.24, P < .001), worsening PUs (beta = 0.04, P = .08; beta = 0.12, P < .001), and infections (beta = 0.41, P < .001; beta = 0.47, P < .001) but not with restraint use, antipsychotic use, or persistent pain. NH influenza vaccination rates were weakly associated with the outcomes (e.g., beta = -0.009, P = .03 for ADL decline, beta = 0.008, P = .07 for infections). Compared with the summer quarter of lowest influenza activity, the results for the other quarters translate to an additional 12,284 NH residents experiencing large ADL decline annually, 15,168 experiencing significant weight loss, 6,284 new or worsening PUs, and 29,753 experiencing infections due to influenza. Conclusion The results suggest a substantial and potentially costly effect of influenza on NH residents. The effect of influenza vaccination on preventing further ADL decline and other clinical outcomes in NH residents should be studied further.