  Nursing homes and other long term-care facilities account for a
disproportionate share of COVID-19 cases and fatalities worldwide. Outbreaks in
U.S. nursing homes have persisted despite nationwide visitor restrictions
beginning in mid-March. An early report issued by the Centers for Disease
Control and Prevention identified staff members working in multiple nursing
homes as a likely source of spread from the Life Care Center in Kirkland,
Washington to other skilled nursing facilities. The full extent of staff
connections between nursing homes---and the crucial role these connections
serve in spreading a highly contagious respiratory infection---is currently
unknown given the lack of centralized data on cross-facility nursing home
employment. In this paper, we perform the first large-scale analysis of nursing
home connections via shared staff using device-level geolocation data from 30
million smartphones, and find that 7 percent of smartphones appearing in a
nursing home also appeared in at least one other facility---even after visitor
restrictions were imposed. We construct network measures of nursing home
connectedness and estimate that nursing homes have, on average, connections
with 15 other facilities. Controlling for demographic and other factors, a
home's staff-network connections and its centrality within the greater network
strongly predict COVID-19 cases. Traditional federal regulatory metrics of
nursing home quality are unimportant in predicting outbreaks, consistent with
recent research. Results suggest that eliminating staff linkages between
nursing homes could reduce COVID-19 infections in nursing homes by 44 percent.
