Care homes that rely heavily on agency staff may be two-and-a-half times more likely to spread COVID-19 to their residents, a study has found.

The research by the University of Strathclyde used a hybrid modelling approach to evaluate the impact of agency/bank staff on the spread of COVID-19 across a network of diverse care homes.

The finding, published in PLOS Computational Biology, confirms existing observational evidence cited in the Journal of Infection and The Lancet Healthy Longevity that the use of agency staff increases the risk of infection for residents compared to staff who work within a single facility.

The study goes on to explore the effect of care home characteristics on their relative vulnerability and the impact of interventions.

In care homes where agency staff comprised on average 10% of the total staff, the risk of infection for residents increased by 2.5 times compared with having sufficient staff and by 1.5 times compared with being understaffed. The model did not account for potentially reduced compliance with measures in understaffed scenarios and lower quality care. 

The modelling showed that agency staff have the biggest infection-risk impact in smaller care homes with lower transmission within their facility and higher staff-to-resident ratios. Agency staff too are more likely to catch the virus compared to permanent staff.

While testing of agency staff was found to be an important risk mitigation measure, the modelling revealed that forming bubbles of care homes and restricting agency staff to only working within a bubble had limited impact on the spread of COVID-19.

Research gap

Co-author of the study, Dr Itamar Megiddo of the Department of Management Science, said: “Care homes are heavily reliant on agency/bank staff due to staff shortages. Consistent with other COVID-19 prevalence surveys in care homes in the UK, our findings would support policies for limiting the movement of staff working across multiple care homes if their testing compliance is low.

“While regular testing with high compliance can help reduce infections, the risk of spread is still higher in homes using agency staff. At the same time, we need to recognise that these staff are necessary to maintain quality of care and the quality of life of residents; an element our study did not explore.

“Our modelling approach helps to fill a research gap in understanding how COVID-19 spreads in care homes and has important policy implications for the sector in terms of developing effective interventions targeting staff working across care homes during the ongoing and future pandemics. “

In the study the researchers combined two simulation approaches – systems dynamics (SD) and agent-based modelling (ABM) into a hybrid model.

Hybrid simulations

Lead author and PhD candidate Le Khanh Ngan Nguyen said: “Both SD and ABM have been used effectively during the COVID-19 pandemic to model infection spread. But each simulation model has its own strengths and weaknesses. We used the SD model to study intra-facility transmission and ABM for inter-facility transmission. Combining both into a hybrid model can help address questions that are difficult to answer with a single approach.

“Despite growing interest in hybrid models, a number of challenges have been raised – the lack of a clear methodological approach to developing hybrid models, the need for multiple expertise, increased cost of using more than one software package and so on. Therefore, the use of hybrid simulations is still limited and only a small number have studied the dynamics of infectious disease transmission across different settings and in fragmented populations.

“Our study helps to advance infectious disease hybrid modelling and demonstrates methods for validating data and building confidence in this kind of approach. The model is now being used to assist decision-makers in the UK Government’s Department of Health and Social Care. “

Previous research by the team, published in the journal Infection Control & Hospital Epidemiology in December 2020, had demonstrated that routine testing of staff is the most effective method of preventing COVID-19 transmission in care home settings. Another study by the team, published in the American Journal of Infection Control in July 2021, found that cohorting is effective in controlling the spread of COVID-19 in care homes.