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Contact Tracing Apps to Identify Potential Exposure to SARS-CoV-2

Last updated: May 20, 2020
Project Number: EN0017-000
Issue: 27
Result type: Report

Contact tracing is a public health intervention that prevents the spread of infectious diseases like COVID-19 by identifying, educating, and monitoring individuals who have been in close contact with infected persons.1 Traditionally, contact tracing is performed manually, which is time-consuming and resource-intensive. New digital contact tracing tools that use smartphone apps to complement existing methods are emerging and may be a technological aide in the prevention of new SARS-CoV-2 (the virus that causes COVID-19) infections.2 Use of contact tracing apps is being explored by governments across Canada.3-5

How It Works

Contact tracing apps use technologies in a smartphone to determine where the users have been or with whom they have been in contact.6 While contract tracing apps that use a smartphone’s GPS to track movement or require the user to produce a Quick Response, or QR, barcode to show they are healthy have been developed or are in use globally, apps that use Bluetooth are emerging as a preferred and less intrusive option for public health authorities.6

Alberta’s ABTraceTogether is one app that uses Bluetooth.7 Users turn on the app whenever they leave their home.8 The app uses Bluetooth to detect other phones using the app and exchanges unique encrypted codes between the devices.8 The app measures how close and how long the user is in “contact” with other devices to help public health officials determine with whom the user has been in close contact (within two metres).8 If the user later tests positive for COVID-19, they are contacted by public health officials and asked to voluntarily upload the app’s encrypted data from the last 21 days to Alberta Health Services.8 Public health officials then use the encrypted data to identify probable close contacts and reach out to the contacts using the phone number provided when setting up the app.8

To help standardize the development and approval of apps, Google and Apple created a set of requirements governments must meet when developing contact tracing apps for Android smartphones and iPhones.9 Groups in the European Union and at the Massachusetts Institute of Technology have also released design recommendations and standards.10,11

Who Might Benefit?

Contact tracing apps are intended to complement existing contact tracing systems.2,11 They are not intended to replace existing methods of contact tracing, nor are they to be used in the absence of these methods.2,11 Rather, the apps are designed to augment the ability of public health officials to identify potential cases of COVID-19 and take appropriate follow-up actions to prevent further spread of the disease.2,11

Availability in Canada

As of May 7, 2020, only Alberta has begun implementing a contact tracing app for COVID-19 — ABTraceTogether.7 Officials in New Brunswick and Newfoundland and Labrador have also publicly begun exploring the use of contact tracing apps.4,5

Globally, contact tracing apps have been developed for use in Australia, China, Egypt, India, Israel, Singapore, and South Korea.2,6,11,12

What Does It Cost?

Our literature search did not identify any information about the costs of developing contact tracing apps or costs associated with their implementation, nor information about the impact contact tracing apps may have on the health care costs associated with COVID-19.

Digital contact tracing using smartphone apps is thought to be less costly compared with traditional contact tracing methods, in part due to their ability to automate manual processes and to scale up in large populations.11 However, it is uncertain whether contact tracing apps are effective without being used with traditional contact tracing methods.2

In Alberta, ABTraceTogether is free to download and use for iPhone and Android smartphones.7 The app requires a smartphone with an active data plan.8

Current Practice

The current standard for identifying individuals who have potentially been exposed to SARS-CoV-2 is traditional or manual contact tracing.11,13 Traditional contact tracing uses public health service employees or volunteers to conduct phone or community outreach.11 Traditional contact tracing processes for potential SARS-CoV-2 exposure may vary by jurisdiction11 but follow the three general steps described by the WHO:14

  • identify an infected individual
  • list all the people the infected individual has encountered
  • monitor and follow up with these contacts for symptoms, and testing for infection.

In the case of SARS-CoV-2, traditional contact tracing processes appear most concerned with people who have been in “close contact” with an infected person and encourage these contacts to self-isolate regardless of symptoms.11

Limitations to traditional contact tracing methods include the time and human resources required to effectively identify contacts and the ability of individuals to remember where they have been and with whom they have been in contact — up to 14 days for SARS-CoV-2 exposure.1,11 The quick rate at which SARS-CoV-2 spreads before signs or symptoms appear also poses challenges to traditional contact tracing approaches.13

A CADTH Rapid Response (published on May 1, 2020) found no evidence-based guidelines, systematic reviews, or health technology assessments for contact tracing for potential exposure to SARS-CoV-2.15

What Is the Evidence?

Our literature search identified two rapid reviews2,11 and one scoping review (pre-publication, not yet peer-reviewed)16 about contact tracing apps or digital contact tracing to identify potential exposure to SARS-CoV-2.

The first rapid review (published on April 20, 2020) found insufficient evidence to support the use of digital contact tracing.2 The authors recommended that readiness for implementing a contact tracing app take into consideration evidence of a need for the technology, availability of widespread testing for the public, the ability of the app to be used consistently by 60% of the population, and an understanding of how the app uses the data it acquires.2 The authors also found that a contract tracing app would only be effective if it is used in addition to manual contact tracing and if it is based on a confirmed diagnostic test for SARS-CoV-2, as opposed to the self-reporting of symptoms.2

The second rapid review (published on April 24, 2020), while largely descriptive, found little published literature on contact tracing apps at that time.11 The authors also noted that a lack of available testing may be slowing the potential impact of contact tracing apps.11

Authors of the scoping review found there was no evidence on uptake and engagement with apps, and a “dearth of evidence” on barriers and facilitators to uptake and engagement.16


No evidence on the safety of contact tracing apps was identified in our literature search.

Issues to Consider

Several important issues about the use of contact tracing apps have been raised.11,12 Contact tracing is predicated on widespread availability of accurate testing.11 Additional issues to consider when implementing this technology include accuracy, uptake, data privacy and security, and health equity.2,11,12


The accuracy of contact tracing apps that use Bluetooth has been raised as a potential impediment to their effectiveness.11 Bluetooth has a range of 10 metres to 30 metres and it is possible that contact tracing apps may connect with devices outside the “close contact” range of two metres. Bluetooth signals can also penetrate walls, and older smartphones may have difficulty determining the user’s orientation to other people.11 Each of these issues creates the potential for false-positive contacts.11 Accuracy may also be impacted should a fractured market of different contact tracing apps emerge.2


The successful application of contact tracing apps also depends on widespread, consistent use in the population.2,5 As of May 5, 2020, only approximately 3% of Alberta’s population had downloaded ABTraceTogether below the estimated 56% to 60% necessary for contact tracing apps to be effective.2,5 Greater adoption may be driven by public trust and confidence, which may in turn be driven by transparent rules and limits for the collection, use, and destruction of data, independent oversight, and legislation.2 The mandatory use of contact tracing apps may be necessary to achieve a sufficient level of uptake but may in turn discourage their use.2,13

Data Privacy and Security

Concern has been expressed that, given the extraordinary nature of the COVID-19 pandemic, government actions such as implementing contact tracing apps may have significant impact on the privacy and fundamental rights of individuals.12,13,17 To balance the right to privacy with the need to prevent the spread of COVID-19, the case for implementing contact tracing apps could be strengthened by minimizing any privacy intrusions, ensuring high standards for data security oversight and protection, and being transparent about how the data collected is used.13 To this end, recommendations for data privacy and security for contact tracing apps have been produced by groups around the world.17,18

Steps taken to protect user privacy include an announcement from Apple and Google that the companies intend to allow only public health authorities to develop contact tracing apps and will bar the use of GPS in any apps developed for their platforms.19

Health Equity

Implementing contact tracing apps that require the user to have a smartphone and know how to use a smartphone may exacerbate existing issues of health equity, particularly in groups at higher risk, such as older adults and people with chronic conditions who may be less likely to use the app.2,11,16

Related Developments

Other strategies being explored to improve the ability to trace potential cases of SARS-CoV-2 include:1,11

  • training non-public health staff and volunteers to perform contact tracing
  • repurposing existing resources such as call centres or hotlines
  • enhancing traditional contact tracing methods using digital tools for data collection.

Looking Ahead

Digital contact tracing is only one part of an holistic public health system.2

Success of digital technologies in the COVID-19 context, including contact tracing apps, may depend on the ability of governments to demonstrate transparency and foster public trust through regulation and oversight in the development, deployment, and phasing out of these solutions.2

By Jeff Mason


  1. Baka A, De Angelis S, Duffell E, et al. Contact tracing for COVID-19: current evidence, options for scale-up and an assessment of resources needed. Solna (SE): European Centre for Disease Prevention and Control; 2020: Accessed 2020 May 13.
  2. Exit through the app store?: a rapid evidence review on the technical considerations and societal implications of using technology to transition from the COVID-19 crisis. (Rapid review evidence). London (GB): Ada Lovelace Institute; 2020: Accessed 2020 May 13.
  3. Tunney C. Ottawa pursuing technological approaches to COVID-19 contact tracing. CBC News 2020 Apr 17; Accessed 2020 May 13.
  4. Bogart N. Canadian officials eye digital contact tracing amid surveillance, privacy concerns. CTV News 2020; Accessed 2020 May 12.
  5. Daigle T. More users needed: lessons from Alberta's coronavirus contact tracing app. CBC News 2020; Accessed 2020 May 11.
  6. Abeler J, Backer M, Buermeyer U, Zillessen H. COVID-19 contact tracing and data protection can go together. JMIR Mhealth Uhealth. 2020;8(4):e19359.
  7. Government of Alberta. ABTraceTogether. 2020; Accessed 2020 May 11.
  8. Government of Alberta. ABTraceTogether FAQ. 2020; Accessed 2020 May 11.
  9. Haskins C. Apple and Google have released their paint-by-numbers recommendations for contact tracing apps. BuzzFeed News 2020; Accessed 2020 May 11.
  10. Massachusetts Institute of Technology. PACT: Private Automated Contact Tracing. 2020; Accessed 2020 May 13.
  11. Rimpilainen S. Rapid review of contact tracing methods for COVID-19. Glasgow (GB): Digital Health & Care Institute, University of Strathclyde; 2020: Accessed 2020 May 13.
  12. Anonymous. Show evidence that apps for COVID-19 contact-tracing are secure and effective. Nature. 2020;580(7805):563.
  13. Parker MJ, Fraser C, Abeler-Dörner L, Bonsall D. Ethics of instantaneous contact tracing using mobile phone apps in the control of the COVID-19 pandemic. J Med Ethics. 2020.
  14. World Health Organization. Contact tracing. 2017; Accessed 2020 May 11.
  15. Contact tracing for potential exposure to SARS-CoV-2 virus: guidelines. (CADTH Reference list). Ottawa (ON): CADTH; 2020: Accessed 2020 May 13.
  16. Thorneloe R, Fynn W, Daly M, et al. Scoping review of mobile phone app uptake and engagement to inform digital contact tracing tools for COVID-19 [non peer-reviewed preprint]. PsyArXiv: doi: 10.31234/; 2020: Accessed 2020 May 13.
  17. Office of the Privacy Commissioner of Canada. Supporting public health, building public trust: privacy principles for contact tracing and similar apps. 2020; Accessed 2020 May 11.
  18. Tracking and tracing COVID: protecting privacy and data while using apps and biometrics. Paris (FR): Organisation for Economic Co-operation and Development; 2020: Accessed 2020 May 13.
  19. Nellis S, Paresh D. Apple, Google ban use of location tracking in contact tracing apps. 2020; Accessed 2020 May 12.