Quantifying Influenza Exposure Within Hospitals And Nursing Homes

Drew Taylor Dickinson

This thesis is restricted to Yale network users only. It will be made publicly available on 08/28/2021



Background: Influenza acquisition in hospitals and nursing homes (NHs) highlights the need for infection prevention to protect patients from contagious diseases while under the care of a healthcare facility. We quantified influenza exposure in both settings and compared facility-onset influenza rates in order to determine if risks of acquiring influenza differed by type of healthcare facility since infection prevention practices are less standardized and less rigorous in NHs.

Methods: We conducted a retrospective cohort study of California hospital and NH inpatients during the 2015-2016 influenza season, defined as the peak influenza month, plus the two adjacent months, using claims data. Exposure-days per average daily census were quantified by summing influenza exposure-days per facility and then dividing by the average daily census of each facility. Hospital-onset influenza (HOI) and nursing home-onset influenza (NHOI) rates were calculated by dividing the number of facility-onset cases by patient-days at-risk, excluding the first two days of stay. NHOI rates were based upon recently admitted patients (first fourteen days of stay) due to the less frequent reporting of claims codes for longer stay residents.

Results: We evaluated events from December 2015 to April 2016. Across 343 hospitals and 1,048 NHs, we calculated 55,970 days of influenza exposure in hospitals and 3,451 days of influenza exposure in NHs. There was a mean of 1.0 (SD: 0.9) influenza hospital exposure-days per average daily census versus a mean of 0.02 (SD: 0.06) influenza NH exposure-days per average daily census during the influenza season (p<0.001). The mean HOI rate was 0.04 (SD: 0.08) influenza cases per 1,000 patient-days and the mean NHOI rate was 0.10 (SD: 0.21) cases per 1,000 recently admitted resident-days (p=0.011) (OR=10.8, 95% CI: 6.2 to 18.9).

Conclusion: Despite having greater influenza exposure, hospitals had nearly an eleven-fold lower rate of facility-onset influenza than NHs, suggesting opportunity for improved infection prevention activities in NHs. Validation of administrative data are needed.