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Estimation of Transmission of COVID-19 in Simulated Nursing Homes With Frequent Testing and Immunity-Based Staffing

Educational Objective
To identify the key insights or developments described in this article
1 Credit CME
Key Points

Question  What are the associations of cohorting, staffing, and testing interventions with COVID-19 transmission in nursing homes?

Findings  In this decision analytical modeling study in a simulated nursing home with 100 residents and 100 staff, routine screening testing and strategies that prioritized pairing recovered staff and recovered residents with susceptible residents were associated with a reduction in transmission of COVID-19 in nursing homes.

Meaning  These findings suggest that frequent testing and immunity-based staffing interventions may reduce transmission of SARS-CoV-2 in nursing homes and protect this vulnerable population.


Importance  Nursing homes and other long-term care facilities have been disproportionately impacted by the COVID-19 pandemic. Strategies are urgently needed to reduce transmission in these high-risk populations.

Objective  To evaluate COVID-19 transmission in nursing homes associated with contact-targeted interventions and testing.

Design, Setting, and Participants  This decision analytical modeling study developed an agent-based susceptible–exposed–infectious (asymptomatic/symptomatic)–recovered model between July and September 2020 to examine SARS-CoV-2 transmission in nursing homes. Residents and staff of a simulated nursing home with 100 residents and 100 staff split among 3 shifts were modeled individually; residents were split into 2 cohorts based on COVID-19 diagnosis. Data were analyzed from September to October 2020.

Exposures  In the resident cohorting intervention, residents who had recovered from COVID-19 were moved back from the COVID-19 (ie, infected with SARS-CoV-2) cohort to the non–COVID-19 (ie, susceptible and uninfected with SARS-CoV-2) cohort. In the immunity-based staffing intervention, staff who had recovered from COVID-19 were assumed to have protective immunity and were assigned to work in the non–COVID-19 cohort, while susceptible staff worked in the COVID-19 cohort and were assumed to have high levels of protection from personal protective equipment. These interventions aimed to reduce the fraction of people’s contacts that were presumed susceptible (and therefore potentially infected) and replaced them with recovered (immune) contacts. A secondary aim of was to evaluate cumulative incidence of SARS-CoV-2 infections associated with 2 types of screening tests (ie, rapid antigen testing and polymerase chain reaction [PCR] testing) conducted with varying frequency.

Main Outcomes and Measures  Estimated cumulative incidence proportion of SARS-CoV-2 infection after 3 months.

Results  Among the simulated cohort of 100 residents and 100 staff members, frequency and type of testing were associated with smaller outbreaks than the cohorting and staffing interventions. The testing strategy associated with the greatest estimated reduction in infections was daily antigen testing, which reduced the mean cumulative incidence proportion by 49% in absence of contact-targeted interventions. Under all screening testing strategies, the resident cohorting intervention and the immunity-based staffing intervention were associated with reducing the final estimated size of the outbreak among residents, with the immunity-based staffing intervention reducing it more (eg, by 19% in the absence of testing) than the resident cohorting intervention (eg, by 8% in the absence of testing). The estimated reduction in transmission associated with these interventions among staff varied by testing strategy and community prevalence.

Conclusions and Relevance  These findings suggest that increasing the frequency of screening testing of all residents and staff, or even staff alone, in nursing homes may reduce outbreaks in this high-risk setting. Immunity-based staffing may further reduce spread at little or no additional cost and becomes particularly important when daily testing is not feasible.

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Article Information

Accepted for Publication: March 21, 2021.

Published: May 14, 2021. doi:10.1001/jamanetworkopen.2021.10071

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Holmdahl I et al. JAMA Network Open.

Corresponding Author: Rebecca Kahn, PhD, Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Dr, Boston, MA 02115 (

Author Contributions: Ms Holmdahl and Dr Kahn had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Ms Holmdahl and Dr Kahn contributed equally to this work, and Drs Buckee and Mina contributed equally to this work.

Concept and design: Holmdahl, Kahn, Buckee, Mina.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: All authors.

Critical revision of the manuscript for important intellectual content: Holmdahl, Kahn, Buckee, Mina.

Statistical analysis: Holmdahl, Kahn, Hay.

Supervision: Buckee, Mina.

Conflict of Interest Disclosures: Dr Kahn reported receiving grants from the National Cancer Institute during the conduct of the study and personal fees from Partners In Health outside the submitted work. Dr Mina reported receiving personal fees from Detect, LivePerson, Abbott Diagnostics, and Roche Diagnostics outside the submitted work. No other disclosures were reported.

Funding/Support: Drs Mina and Kahn are supported by the U01 Serological Centers of Excellence Grant. Drs Mina and Hay are supported by the DP5 National Institutes of Health Director’s Award.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: Rachel Slayton, PhD (Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, US Department of Health and Human Services), provided discussions and feedback and was not compensated for this work.

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