An agent-based model to assess the impact of shared staff and occupancy rate on infectious disease burden in nursing homes

Abstract

Infectious diseases can propagate between nursing homes through asymptomatic staff members who are employed at multiple facilities. However, the transmission dynamics of infections, both within individual nursing homes and across facilities, has been less investigated. To fill this gap, we developed an agent-based model of two nursing homes extendible to a network of n nursing homes connected with different percentages of shared staff. Focusing on the outbreaks of COVID-19 in U.S. nursing homes, we calibrated the model according to the COVID-19 prevalence data and estimated levels of shared staff for each State. The model simulations indicate that reducing the percentage of shared staff below 5% plays a significant role in controlling the spread of infection from one nursing home to another through personal protective equipment usage, rapid testing, and vaccination. As the percentage of shared staff increases to more than 30%, these measures become less effective, and the mean prevalence of infection reaches a steady state in both nursing homes. The hazard ratios for infection and mortality indicate that nursing homes with higher occupancy rates are more significantly affected by increased staff-sharing percentages. In conclusion, the burden of infection significantly increases with greater staff sharing between nursing homes, particularly in high-occupancy facilities, where transmission dynamics are amplified due to greater resident density and staff interactions.

Keywords: Agent-based model; COVID-19; GAMA; Infection; Nursing home; Shared staff.

Fig. 1

The floor plan for two nursing homes (NH1 and NH2) considered in the agent-based model. Agents can be susceptible, infectious, or recovered. For each simulation, a certain percentage of staff is shared in both nursing homes. Staff are divided into three different types: registered nurses (RN), licensed practical nurses (LPN), and registered nursing aids (RNA)

Fig. 2

Schematic diagrams of the proposed Agent-Based model. a COVID-19 infection can spread within each nursing home by infectious residents and staff. It can also spread from one nursing home to another by asymptomatic staff members working in both nursing homes, (b) Residents of each nursing home can enter each state according to their vaccination and health status

Fig. 3

Estimated percentage of staff working in more than one nursing home facility according to each state

Fig. 4

The independent variable significance ranking based on the (a) staff and (b) resident COVID-19 prevalence

Fig. 5

Simulated prevalence boxplots of COVID-19 infection in NH1 residents were fitted to weekly prevalence data of six different states (shown with red bars) associated with the emergence of Omicron variant (weeks from November 28, 2021, to February 27, 2022). There is a fair amount of agreement between the model simulations and the prevalence data

Fig. 6

Simulated cumulative prevalence of COVID-19 among staff and residents of nursing homes 1 and 2. Increasing the shared staff results in an increase in the cumulative prevalence

Fig. 7

Hazard ratios of infection and mortality as a function of percent shared staff. The escalation of shared staff levels results in a substantial increase in (a) the hazard ratio of mortality and (b) the likelihood for residents of both nursing homes to contract COVID-19 infection