Contact Tracing for COVID-19

Last Updated: November 18, 2020

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This Briefing Note was completed by the Research, Analysis, and Evaluation Branch (Ministry of Health) based on information provided by members of the COVID-19 Evidence Synthesis Network. Please refer to the Methods section for further information.

Purpose

This note summarizes the evidence and jurisdictional experiences on contact tracing approaches used to contain the COVID-19 pandemic.

*The full version of the Briefing Note including the Appendix can be accessed in the PDF file at the top of the page*

Key Findings

Analysis for Ontario

Implementation Implications

Large-scale manual contact tracing is key in most contexts, but can be further supplemented with digital contact tracing approaches if privacy and usability limitations are addressed.

Context and Terminology

Contact tracing is the process of identifying, assessing, and managing people who have been exposed to a disease to prevent onward transmission. A study (May 27, 2020) on contact tracing for coronavirus disease 2019 (COVID-19) described traditional and digital contact tracing approaches:

  • Traditional Contact Tracing: Public health officials interview an infected individual, identify contacts, and advise exposed contacts to self-monitor for symptoms, self-quarantine, or obtain medical evaluation and treatment. This approach has had success in reducing infection transmission in many epidemics, including severe acute respiratory syndrome-associated coronavirus (SARS-CoV) and Ebola. However, some limitations of this approach include being labour- and time-intensive, making it challenging to scale.
  • Digital Contact Tracing: Electronic information has the potential to address limitations of traditional contact tracing, such as scalability, notification delays, recall errors, and contact identification in public spaces.
    • Bluetooth-Based Approaches: Most COVID-19 contact tracing application (apps) use Bluetooth signal strength to infer distance and define exposure status based on distance from and duration of proximity to an individual subsequently identified as infected.
    • Location-Based Approaches: These contact tracing approaches do not require Bluetooth. Instead, they use cell phone network data, Global Positioning System (GPS), Wi-Fi signals, and other smartphone sensors to identify the geolocations of users and proximity to infected individuals.
      • A Briefing Note on Using Quick Response (QR) Codes for Contact Tracing is available on the Evidence Synthesis Network website.

Supporting Evidence

This section summarizes the scientific evidence and jurisdictional experiences regarding contact tracing approaches during the COVID-19 epidemic. In terms of information on jurisdictional experience, most of the information presented is based on case study findings on how Germany, Iceland, Israel, Singapore, South Korea, and Taiwan contained the COVID-19 epidemic through rigorous contact tracing. Additional information on other jurisdictions was included if available.

Scientific Evidence

  • No relevant evidence-based guidelines have been identified regarding contact tracing for people who have been in contact with a person with a suspected or confirmed diagnosis of COVID-19; thus, no conclusions can be drawn.

International Scan

  • Traditional Contact Tracing Approaches: Germany, Iceland, Israel, Singapore, South Korea, and Taiwan primarily rely on traditional contact tracing approaches, in which contacts are identified through a thorough review of available data (e.g., telephone interviews with the infected individual, family, and/or physician; travel or police records; credit card transactions; closed-circuit television footage). In general, contact tracing teams within local public health units call infected individuals to communicate test results and/or inquire about any contacts that occurred in the days preceding symptom onset.
  • Digital Contact Tracing Approaches: The most commonly used digital approaches involve smartphone apps using GPS (e.g., Israel, Iceland) or Bluetooth data (e.g., Singapore, Australia, United Kingdom, Germany), as well as linked data and cloud-based technologies (e.g., South Korea, Taiwan). Other digital approaches include:
    • Quick Response (QR) Codes added to public venues to enable identification of contacts should an outbreak occur (e.g., Singapore, New Zealand). For example:
      • New Zealand’s NZ COVID Tracer voluntary app creates a digital diary of the places users visit by users scanning QR code posters that contain information about the name and location of businesses. It is meant to support manual contact tracing conducted by public health units and the National Close Contact Service.
    • Germany launched a smartwatch app that collects pulse, temperature, and sleep pattern data to screen for signs of viral illness. Data are presented on an online, interactive map in which authorities can assess the likelihood of COVID-19 incidence across the country
    • Massachusetts Institute of Technology (MIT) Review’s Covid Tracing Tracker is a database that captures details (e.g., mandatory vs. voluntary, number of users and penetration rate, centralized vs. decentralized, data destruction, type of technology) of automated contact tracing efforts backed by national governments around the world.
    • A summary of available contact tracing solutions is presented here (as of November 2020).
  • Maintaining Surveillance and Capacity: Key factors that may have contributed to effective contact tracing include:
    • Mounting an early response: Many jurisdictions began implementing public health measures before the first imported case was detected (e.g., activating taskforces, initiating testing among symptomatic international travellers), which enabled them to coordinate multiple sectors of government for a proactive response.
    • Human resource capacity for contact tracing: Although manual contact tracing is the preferred approach, it is very resource-intensive and may rapidly become overwhelmed. Human resource capacity for contact tracing in most jurisdictions was achieved through redeployment and training of employees and volunteers across governmental and nongovernmental sectors (e.g., health care workers, medical students, armed forces, police)
      • The number of contact tracers range from: five per 20,000 inhabitants in Germany (as of late April 2020), 52 contact tracers in Iceland (as of late March 2020), 200+ in New Zealand (as of May 29, 2020), 240 in San Francisco (as of late April 2020), more than 1,300 in Singapore (as of September 2020), and 1,800 teams, each with at least five members, in Wuhan, China (as of late February 2020).
      • In Taiwan, central and regional governmental epidemiologists lead local health department teams in contact tracing. The first round of case investigation is usually completed within 10 hours, accomplished by teams working extended hours (as of July 2020).
  • Effectiveness: It may not be possible to directly attribute containment of the COVID-19 epidemic to any single public health measure. Nonetheless, Singapore, Iceland, Taiwan, and South Korea did not impose a national lockdown, which supports at least partial effectiveness of contact tracing approaches. For instance, Taiwan and Singapore have had success in containing the outbreak without a lockdown initially and over time. Moreover, Iceland presents compelling evidence supporting the effectiveness of rigorous contact tracing to limit further transmission, with high rates of accurate identification of imported versus community-linked COVID-19 cases and those in isolation or quarantine.
    • Bluetooth, global positioning system, and cloud-based technologies may serve as useful tools for supporting contact tracing, particularly in densely populated areas where not all contacts may be known to the infected individual.
      • However, due to privacy and usability concerns, digital contact tracing tools may best serve as supplementary measures to traditional contact tracing. This approach has been recommended by the World Health Organization.
    • A research commentary noted that Germany, Singapore, and South Korea have successfully adopted and integrated digital contact tracing technologies, which may be associated with the early flattening of incidence curves and low mortality rates.
  • Challenges: Some jurisdictions are experiencing low uptake of digital contact tracing apps due to privacy, technology, and strategy limitations:
    • In South Korea, sharing outbreak data has created public discrimination and prevented people from getting tested.
    • Israelis have started using cellphone holsters to block location tracking.
    • France’s centralized app has been limited by user uptake, as it continues to experience battery drain, collects more personal information than advertised, and is not interoperable with neighbours’ decentralized apps.
    • The US falls behind other countries that have used technology to augment traditional contact tracing strategies in the COVID-19 response as a result of privacy concerns and the absence of a coordinated national strategy (requiring states to develop their own approaches).
    • In Singapore, population uptake of the TraceTogether app was not sufficient to replace manual contact tracing (less than one-fifth of the population had downloaded the app two months after its launch). Issues included privacy concerns, technical limitations, and necessity for a smartphone for participation.

Canadian Scan

  • The Public Health Agency of Canada developed guidance for federal/provincial/territorial public health authorities to support the management of cases and contacts of COVID-19 within their jurisdictions. It includes recommendations for frequency and type of follow-up stratified by exposure risk level (low, medium, or high)
    • For example, British Columbia (May 15, 2020) and Nova Scotia (May 22, 2020) have issued interim guidance on case and contact management for COVID-19.
  • Only one province was identified that has moved towards using a digital contact tracing approach.
    • Alberta’s ABTraceTogether is a mobile contact tracing app using Bluetooth that can be voluntarily downloaded by users to let them know if they have been exposed to or have exposed others to COVID-19. It is a tool to complement traditional manual contact tracing completed by public health officials who work at Alberta Health Services (AHS). Personal data is only stored on the user’s phone for 21 days in an encrypted format; it can only be shared with AHS contact tracers with the user’s permission
  • The Canadian firm, BlueDot, disseminates near-real-time insights on COVID-19 movements to clients, including governments, hospitals, and airlines, based on over 40 pathogen-specific datasets reflecting disease mobility and outbreak potential.
  • According to a review (September 3, 2020), the Directorate of Force Health Protection within the Canadian Armed Forces will be developing training for allied health professionals to assist with contact tracing and follow-up, and will ensure adequate resources are in place to manage surge capacity for COVID-19.

Ontario Scan

  • On April 27, 2020, the Government of Ontario released its framework document for reopening the province, echoing the need to strengthen public health capacity for rigorous testing, timely contact tracing, and case management.
    • One of the criteria being considered for determining when to ease public health measures and for ongoing monitoring of progress is that approximately 90% of new COVID-19 contacts are being reached by local public health officials within one day, with guidance and direction to contain community spread.
  • Public Health Ontario, in collaboration with the Ministry of Health and the federal government, is leading the COVID-19 Contact Tracing Initiative. To date, contact tracing is led by Ontario’s public health units, but additional capacity is required because of the rising number of cases and contacts to manage.

Methods

The COVID-19 Evidence Synthesis Network is comprised of groups specializing in evidence synthesis and knowledge translation. The group has committed to provide their expertise to provide high-quality, relevant, and timely synthesized research evidence about COVID-19 to inform decision makers as the pandemic continues. The following members of the Network provided evidence synthesis products that were used to develop this Evidence Synthesis Briefing Note:

  • Ontario Health (Cancer Care Ontario). (May 18, 2020). Personal Communication to Research, Analysis and Evaluation Branch.
  • Ontario Health (Quality). (May 18, 2020). Personal Communication to Research, Analysis and Evaluation Branch.
  • Unity Health – St. Michael’s Hospital. (May 18, 2020). Personal Communication to Research, Analysis and Evaluation Branch.

For more information, please contact the Research, Analysis and Evaluation Branch (Ministry of Health).