Influenza Illness and Hip Fracture Hospitalizations in Nursing Home Residents: Are They Related?

Background: Influenza illness may impact the risk of falls and fractures during acute illness due to unsteady gait or dizziness. We evaluated the association between influenza and hip fracture hospitalizations in long-stay (LS) nursing home (NH) residents. Methods: We analyzed weekly rates of hospitalization in a retrospective cohort of LS NH residents between January 1, 2000 to December 31, 2009. Hip fracture and influenza like illness (ILI) hospitalizations were identified with Medicare fee-for-service part A claims. We evaluated unadjusted and adjusted models with the primary exposures, weekly rate of influenza-like illness hospitalizations, city-wide mortality, and NH influenza vaccination rate and primary outcome of weekly rate of hip fracture hospitalizations. Results: There were 9,237 incident hip fractures in the cohort. Facility wide ILI hospitalization rate was associated with the hip fracture hospitalization rate in the unadjusted (incidence rate ratio [IRR] 1.13, 95% confidence interval [CI]: 1.08, 1.17) and adjusted (IRR 1.13, 95% CI: 1.09, 1.18) analyses. City-wide influenza mortality was associated with hip fracture hospitalization rates for the unadjusted (IRR 1.03, 95% CI: 1.02, 1.04), and adjusted (IRR 1.02, 95% CI: 1.01, 1.03) analyses. NH influenza vaccination rates were not associated with changes in hip fracture hospitalization rates. Conclusions: ILI hospitalizations are associated with a 13% average increase in hip fracture hospitalization risk. In a given NH week, an increase in the number ILI hospitalizations from none to two was associated with an approximate one percentage point increase in hip fracture hospitalization risk. Strategies to reduce influenza risk should be investigated to reduce hip fracture risk.