Effectiveness of contact tracing

Effectiveness of contact tracing in the control of infectious diseases: a systematic review

CPD Hours: 1
Current as at 06 June 2022
Contact tracing plays an important role in the control of emerging infectious diseases, but little is known yet about its effectiveness. Contact tracing of symptomatic infected patients works on an intermediate level: treatment or quarantine of contactees may be effective because unidentified infected patients are most likely to be found among contactees, and efficient because the resources can be directed towards individuals at risk only.

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Understand what is involved in contact tracing in the management of infectious diseases

Course Content

Research into disease transmission and mobility falls into two broadly distinct topics. The first deals with how long-distance travel drives the spatial diffusion of epidemics across areas (such as cities or regions) and the second with how local travel (within cities and neighbourhoods) drives the local transmission. These two aspects are intertwined, such that they are often considered and modelled simultaneously.

Contact tracing plays an important role in the control of emerging infectious diseases, but little is known yet about its effectiveness. Contact tracing of symptomatic infected patients works on an intermediate level: treatment or quarantine of contactees (by contact we mean the possible transmission event, by contactee the individual that is contacted) may be effective because unidentified infected patients are most likely to be found among contactees, and efficient because the resources can be directed towards individuals at risk only.

Tracing and quarantine have been successfully applied for, for example, smallpox control, where the term ‘Leicester method’ refers to exactly this strategy, with the establishment of specific smallpox hospitals. It was also successful during the SARS epidemic, but not during the British foot-and-mouth epidemic. Contact tracing has played a central role in COVID-19 control in many jurisdictions and is often used in conjunction with other measures such as travel restrictions and social distancing mandates. Contact tracing is made ineffective, however, by delays in testing, calling, and isolating.

The effectiveness of contact tracing for any infectious disease is limited by how quickly contacts can be informed compared with the infectious period. If contact tracing teams reach an individual’s contacts only toward the end of their infectious period, very few further infections will be prevented. Several delays in the process make rapid contact tracing challenging: the time to develop symptoms, to seek a test, to get test results, and for contact tracing teams to reach contacts.

Overall, this study demonstrates the feasibility of using realistic contact networks estimated from contact tracing data to develop scenario projections for understanding the drivers of disease spread. In contrast to other approaches, mobility data makes it possible to explore how contacts contribute to disease spreading. They can further enable us to assess the role played by super-spreading individuals, who infect a high number of other people, and study how epidemics spread within and across social communities.

Learning Outcomes

In this session, you will:

  • Understand what is involved in contact tracing in the management of infectious diseases
  • Investigate the effects of contact tracing methods
  • Discuss the impact of various tracing programs and how contact tracing influences the disease control
  • Review how contact tracing informs public health decision making

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