Skip to main content

Optimal COVID-19 quarantine and testing strategies

Our take —

In this study, available as a preprint and thus not yet peer reviewed, authors used a mathematical model to quantify how different testing strategies could be used to reduce the probability of transmitting SARS-CoV-2 to others after leaving quarantine. Any testing during the quarantine period, especially toward the end, contributed to a reduction in the probability of post-quarantine transmission (pPQT). The pPQT was reduced by 98% and 93% for 7-day and 5-day quarantines respectively with PCR testing for SARS-CoV-2 upon entrance and exit into quarantine, as compared to a 3-day quarantine with only entrance testing. Many assumptions in the model, such as an optimistic diagnostic sensitivity and just a 24-hour delay from sampling to returning a test result, may not be realistic or feasible in most settings. However, this work provides a framework to explore how quarantine measures could be adapted to incorporate additional information from test results.

Study design

Modeling/Simulation

Study population and setting

Using a mathematical model, authors explored if different quarantine durations combined with testing at the start and/or end of the quarantine period could have the equivalent reduction in the probability of post-quarantine transmission (pPQT) as the standard 14 day quarantine period with no testing. They explored three scenarios for which quarantine may be needed: ii) for travel regulations; ii) quarantine of contacts identified through contact tracing; and iii) case isolation upon symptom onset. Authors then used a dataset of 4,040 PCR test results from tests administered between April 11 to August 26, 2020 at an offshore oil rig to test their model. They assumed an 8.29 day incubation period and a 24 hour delay between sampling and test results being returned.

Summary of Main Findings

Any testing during the quarantine period contributed to a reduction in the pPQT, with the reduction dependent on the timing of the test and the duration of quarantine. A single test at the end of quarantine of any length consistently resulted in a lower pPQT compared to a single test conducted at the start of quarantine. Optimum time for testing was upon exit from quarantine, day 5, and day 6 for quarantine lasting ≤7 days, 8-13 days, and ≥14 days respectively. In an optimistic scenario with minimal delays to test results, testing at the end (or beginning and end) of quarantine could halve the duration to 7 days. Analysis of the 4,040 PCR test results conducted on an oil rig where workers were tested at the start of a 3-day quarantine, using this framework found that adding a test at the end of a 7 day or 5-day quarantine could reduce the pPQT by 98% and 93% respectively. Authors estimated that 9 offshore transmission events could have resulted in the absence of testing on exit.

Study Strengths

Authors consider several real-world scenarios where quarantine is currently implemented and explore several scenarios for testing and quarantine duration. Their framework is then validated using a large dataset of 4,040 PCR test results conducted amongst employees of offshore oil rigs. Authors also tested if the duration an individual is infected but less likely to infect contacts had an impact on their results.

Limitations

Authors assumed that the incubation period is fixed at 8.29 days which may be unrealistic given the mean incubation period estimated from multiple studies is shorter at 5 – 7 days. The incubation period can also vary between individuals which the authors do not account for in this study. Authors also extrapolated test sensitivity estimates early after contact exposure based on data from hospitalised patients; the diagnostic sensitivity assumptions appear quite optimistic relative to other available data based on more comprehensive data from clinically diverse patient populations. Given their study focuses on the use of testing for release from quarantine we would expect this would also include asymptomatic and/or mild individuals where test sensitivity may differ substantially. Finally, they also made an optimistic assumption that the delay from sampling to receiving test results is 24 hours which may not be realistic or feasible in many settings. The data set used to validate their framework represents a unique closed population which is not representative of the wider population.

Value added

With many countries adopting testing on arrival or as a prerequisite for travel, this study quantifies the value of testing at the end of the quarantine period in addition to, or in place of testing at the beginning of the quarantine period.

This review was posted on: 3 January 2021