Perfect as the enemy of good: tracing transmissions with low-sensitivity tests to mitigate SARS-CoV-2 outbreaks

Abstract

Throughout the COVID-19 pandemic, governments and individuals have attempted a wide variety of strategies to limit the damage of the pandemic on human lives, population health, and economies. Contact tracing has been a commonly used strategy, and various approaches have been proposed and attempted. We summarise some methods of contact tracing and testing, considering the resources demanded by each and how features of SARS-CoV-2 transmission affect their effectiveness. We also propose an approach focusing on tracing transmission events, which can be particularly effective when superspreading events play a large role in transmission. Accounting for the best available evidence on a pathogen and for the availability of resources can make control strategies more effective, even if they are not perfect.

Figure 1

Schematic presentation of three approaches to test and trace contacts of infected individuals Transmission tracing (A). Quarantine of all identified contacts (B). Isolation of contacts who are tested and found to be positive for the pathogen (C).

Figure 2

Effectiveness and isolation burden of the transmission tracing strategy in different settings Proportion of secondary cases isolated under the transmission tracing strategy (top row) and proportion of index cases whose contacts are isolated under the transmission tracing strategy (bottom row) versus test sensitivity by R₀ and k. The diagonal line in the top row indicates the proportion of secondary cases who test positive and are isolated under strategy C (figure 1).