Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Endo, Akira; Leclerc, Quentin J.; Knight, Gwenan M.; Medley, Graham F.; Atkins, Katherine E.; Funk, Sebastian; Kucharski, Adam J.

doi:10.12688/wellcomeopenres.16344.3

Cited by 63 publications

(53 citation statements)

References 18 publications

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“…However, even with just forward tracing, epidemic control is still theoretically achievable. Several recent studies have produced similar findings 26 , 29 , 30 .…”

Section: Resultssupporting

confidence: 62%

Controlling COVID-19 via test-trace-quarantine

et al. 2021

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Initial COVID-19 containment in the United States focused on limiting mobility, including school and workplace closures. However, these interventions have had enormous societal and economic costs. Here, we demonstrate the feasibility of an alternative control strategy, test-trace-quarantine: routine testing of primarily symptomatic individuals, tracing and testing their known contacts, and placing their contacts in quarantine. We perform this analysis using Covasim, an open-source agent-based model, which has been calibrated to detailed demographic, mobility, and epidemiological data for the Seattle region from January through June 2020. With current levels of mask use and schools remaining closed, we find that high but achievable levels of testing and tracing are sufficient to maintain epidemic control even under a return to full workplace and community mobility and with low vaccine coverage. The easing of mobility restrictions in June 2020 and subsequent scale-up of testing and tracing programs through September provided real-world validation of our predictions. Although we show that test-trace-quarantine can control the epidemic in both theory and practice, its success is contingent on high testing and tracing rates, high quarantine compliance, relatively short testing and tracing delays, and moderate to high mask use. Thus, in order for test-trace-quarantine to control transmission with a return to high mobility, strong performance in all aspects of the program is required.

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“…However, even with just forward tracing, epidemic control is still theoretically achievable. Several recent studies have produced similar findings 26 , 29 , 30 .…”

Section: Resultssupporting

confidence: 62%

Controlling COVID-19 via test-trace-quarantine

et al. 2021

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“…Once adapted to the UK policy, we used our model to assess the effectiveness of a ‘backwards tracing’ strategy, which aims to identify a case's infector and allows for the identification of more branches of transmission when compared to forwards tracing. We, and other groups [ 35 , 36 ], found that in theory it could improve contact tracing, but also that implementation challenges could reduce this effect. Ultimately, the NHS Test and Trace programme in England continued to use forwards tracing for standard cases not associated with a particular list of high-risk settings.…”

Section: In Contextmentioning

confidence: 89%

“…Backwards contact tracing is when the direction of tracing is opposite to the direction of transmission, which results in the traced individual being the infector of the case who initiated the tracing attempt. For some diseases, backwards tracing can be an important strategy as a backwards step can then be followed by a forwards tracing step again to discover ‘sibling’ infections who share the same infector [ 35 ]. A visualization of backwards and forwards tracing is plotted in figure 1 , where a successful backwards tracing event leads to the quarantine of a sibling chain of transmission.…”

Section: Contact Tracing Isolation Strategies and Considerations Post-lockdownmentioning

confidence: 99%

Using a household-structured branching process to analyse contact tracing in the SARS-CoV-2 pandemic

Fyles¹,

Fearon

Overton

et al. 2021

Phil. Trans. R. Soc. B

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We explore strategies of contact tracing, case isolation and quarantine of exposed contacts to control the SARS-CoV-2 epidemic using a branching process model with household structure. This structure reflects higher transmission risks among household members than among non-household members. We explore strategic implementation choices that make use of household structure, and investigate strategies including two-step tracing, backwards tracing, smartphone tracing and tracing upon symptom report rather than test results. The primary model outcome is the effect of contact tracing, in combination with different levels of physical distancing, on the growth rate of the epidemic. Furthermore, we investigate epidemic extinction times to indicate the time period over which interventions must be sustained. We consider effects of non-uptake of isolation/quarantine, non-adherence, and declining recall of contacts over time. Our results find that, compared to self-isolation of cases without contact tracing, a contact tracing strategy designed to take advantage of household structure allows for some relaxation of physical distancing measures but cannot completely control the epidemic absent of other measures. Even assuming no imported cases and sustainment of moderate physical distancing, testing and tracing efforts, the time to bring the epidemic to extinction could be in the order of months to years. This article is part of the theme issue ‘Modelling that shaped the early COVID-19 pandemic response in the UK’.

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“…It may not be easily extensible to settings such as schools or workplaces. Alternative strategies also exist, including tracing of contacts-of-contacts [ 38 ] and so-called backwards tracing [ 39 ]. The latter approach is part of a fundamentally different way of using contact tracing in disease control that has been used in COVID-19 response in some countries (e.g., Japan [ 40 ]), which focuses on identifying settings that have the potential to facilitate superspreading events or otherwise amplify transmission.…”

Section: Discussionmentioning

confidence: 99%

Maximizing and evaluating the impact of test-trace-isolate programs: A modeling study

et al. 2021

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Background Test-trace-isolate programs are an essential part of coronavirus disease 2019 (COVID-19) control that offer a more targeted approach than many other nonpharmaceutical interventions. Effective use of such programs requires methods to estimate their current and anticipated impact. Methods and findings We present a mathematical modeling framework to evaluate the expected reductions in the reproductive number, R, from test-trace-isolate programs. This framework is implemented in a publicly available R package and an online application. We evaluated the effects of completeness in case detection and contact tracing and speed of isolation and quarantine using parameters consistent with COVID-19 transmission (R0: 2.5, generation time: 6.5 days). We show that R is most sensitive to changes in the proportion of cases detected in almost all scenarios, and other metrics have a reduced impact when case detection levels are low (<30%). Although test-trace-isolate programs can contribute substantially to reducing R, exceptional performance across all metrics is needed to bring R below one through test-trace-isolate alone, highlighting the need for comprehensive control strategies. Results from this model also indicate that metrics used to evaluate performance of test-trace-isolate, such as the proportion of identified infections among traced contacts, may be misleading. While estimates of the impact of test-trace-isolate are sensitive to assumptions about COVID-19 natural history and adherence to isolation and quarantine, our qualitative findings are robust across numerous sensitivity analyses. Conclusions Effective test-trace-isolate programs first need to be strong in the “test” component, as case detection underlies all other program activities. Even moderately effective test-trace-isolate programs are an important tool for controlling the COVID-19 pandemic and can alleviate the need for more restrictive social distancing measures.

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Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Cited by 63 publications

References 18 publications

Controlling COVID-19 via test-trace-quarantine

Controlling COVID-19 via test-trace-quarantine

Using a household-structured branching process to analyse contact tracing in the SARS-CoV-2 pandemic

Maximizing and evaluating the impact of test-trace-isolate programs: A modeling study

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