Testing rate and contact tracing key to successful re-opening of Ontario


TORONTO, May 21, 2020 – Enhanced testing and contact tracing for the coronavirus in Ontario could allow physical distancing measures to be relaxed, while keeping the reproduction ratio under one and preventing a second wave of infections, says corresponding author of a new modelling study Distinguished Research Professor Jianhong Wu of York University’s Faculty of Science.

The de-escalation would include three phases – a re-opening of workplaces, a resumption of public events and activities, followed by the opening of schools. The researchers modelled the requirement for testing, contact tracing and quarantine for each phase.

To be successful in the first two phases, the current time for diagnosis needs to be maintained and almost 60 per cent of exposed contacts would have to be traced, quarantined and isolated. Although, if some level of social distancing is maintained, that could counter any decrease in quarantining.

In the third phase, the researchers found that 70 per cent of exposed contacts would need to be isolated to avoid a rebound, a value they say is unrealistic. The use of masks and personal protective equipment during de-escalation, however, could be an important tool in helping to prevent a rebound.

“Our analysis can help inform public health and policy makers on best future actions and interventions to control the outbreak while relaxing physical distancing,” says Wu, director of the Advanced Disaster, Emergency and Rapid Response Simulation Program.

The researchers looked at different possibilities and scenarios involving de-escalation of the current physical distancing and isolation rules for all of Canada, but particularly in Ontario. The province closed schools on March 14 and declared a state of emergency on March 17 with the closure of non-essential workplaces as of March 24.

The study estimated the effectiveness of interventions in terms of contact rate, probability of transmission per contact, detection rate, and proportion of isolated contacts. They concluded that a feasible de-escalation approach is to reverse the steps taken that led to most workplace and school closures.

In the future, the researchers say a transmission model involving age-specific contact mixing could be used to determine logistic implementations of a wider range of de-escalation strategies that would be dependent on a person’s age and the setting, whether a school, workplace, the home or community.

The research was published in the journal Biology.

Find out more about how York University is creating positive change in the COVID-19 pandemic here.


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Sandra McLean, York University Media Relations, 416-272-6317, sandramc@yorku.ca