# Connectivity between long-term care homes and subsequent SARS-CoV-2 outbreaks

## TL;DR

This study found that workers moving between long-term care homes increased the risk and timing of SARS-CoV-2 outbreaks, but not their size.

## Contribution

The study introduces a novel analysis linking staff movement between care homes to the risk and timing of SARS-CoV-2 outbreaks.

## Key findings

- Higher staff connectivity between long-term care homes increased outbreak risk by 8% per additional connection.
- Staff connectivity was linked to earlier outbreak onset but not outbreak size.
- Structural improvements in facilities are crucial to manage outbreaks after initial infection importation.

## Abstract

To examine the relationship between individual workers employed at more than one LTCH (inter-LTCH connectivity) across LTCH and SARS-CoV-2 outbreaks.

We conducted a retrospective cohort study using secondary, aggregate data (surveillance and mobile geolocation data) from 179 LTCH in the Greater Toronto Area of Ontario, the province where close to one-third of the Canada’s SARS-CoV-2 cases among long-term care homes residents were reported, between 2020-02-26 and 2020-08-31. The main exposure of interest was the inter-LTCH connectivity, generated from geographic location data procured across mobile apps. Three outcomes were examined: 1) at least one SARS-CoV-2 diagnosis among residents, 2) cumulative cases among residents in each facility, and 3) time to first outbreak.

The median degree of connectivity for LTCH that experienced an outbreak (59%; 106/179) was 1.2 times the degree of those without an outbreak (6 compared to 5). LTCH with higher inter-LTCH connectivity also had larger numbers of residents and beds, and were more likely to have for-profit ownership. After adjusting for facility-level and neighbourhood-level factors, every additional connection to another LTCH increased the odds of an outbreak in the respective LTCH by 8% (adjusted odds ratio=1.08, 90% credible interval [CrI]: 1.02-1.09). Inter-LTCH connectivity was also associated with higher risk of earlier occurrence of a first SARS-CoV-2 case (adjusted hazard ratio=1.05, 90%CrI: 1.02-1.09), but not with outbreak size.

Staff cohorting was associated with reduced importation risk of SARS-CoV-2 cases into LTCH. However, once importation has occurred, other facility-level factors including facility infrastructure and staff benefits are more important in shaping outbreak size. Implementing these structural strategies to meet the LTCH workers and residents’ needs are pivotal to prevent and manage future respiratory virus outbreaks.

The online version contains supplementary material available at 10.1186/s12889-025-23621-3.

Were movement of long-term care homes (LTCH) workers between facilities (staff connectivity) associated with the risk, size, and timing of SARS-CoV-2 outbreaks in these facilities during the first wave of the COVID-19 pandemic.

After adjusting for facility-level and neighbourhood-level factors, a higher degree of staff connectivity between LTCH was associated with a greater risk of outbreaks (2.2-fold the risk of a LTCH connected with 10 more other LTCHs) and a higher risk of experiencing an earlier outbreak (1.7-fold the hazard with 10 more staff connections with other LTCH). However, we did not observe an association between connectivity and the size of outbreaks.

“One-site” strategy to cohort staff by facility and minimizing movement may reduce risk of pathogen importation. However, structural strategies (e.g. improve facility design and infrastructure) to reduce nosocomial transmission within these facilities remain pivotal to prevent and manage future respiratory virus outbreaks.

The online version contains supplementary material available at 10.1186/s12889-025-23621-3.