Contact Tracing

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This page collects observations, interpretations, and consequences action about the Contact Tracing as an intervention for SARS-CoV2 in general. Please observe the structure of the page, when you add your content. Please use references where possible. Remember to find the relevant page. For example, if your observation is about transmission routes, please use that page, instead of posting your content here.

Principles of contact tracing

Contact tracing .jpg Contact Tracing (Artwork by Nicky Case. Creative Commons)

The idea of contact tracing is to rapidly identify ALL persons who have been in close contact with a patient during the contagious period. Identified contacts should be (self) quarantined and monitored for the maximum duration of an incubation period, and tested as soon as symptoms appear. In some situations, testing can be added to the monitoring, regardless of symptoms. The aim is to identify new cases and isolate them timely.

WHO COVID19 Contact Tracing Guidelines

  • Critical elements of the implementation of contact tracing are community engagement and public support; careful planning and consideration of local contexts, communities, and cultures; a workforce of trained contact tracers and supervisors; logistics support to contact tracing teams; and a system to collate, compile, and analyse data in real-time. [1]
  • Because individuals may transmit COVID-19 while pre-symptomatic or asymptomatic, this guidance also emphasizes the importance of quarantining contacts to further reduce the potential for secondary transmission. [1]
  • Contact tracing may be difficult when the transmission is intense (community transmission) but should be carried out as much as possible. [1]
  • When countries have passed the peak of transmission and case numbers are decreasing, and particularly when stringent public health and social measures are being adjusted, rapid identification of cases and contact tracing are critical to maintain low levels of transmission and rapidly identify and break new transmission chains.[1]
  • In case of public gatherings:[1]
    • Undertake a local risk assessment and collaborate with organizers/leadership to notify potential contacts either actively or passively (for example, through ‘warn and inform’ messages to an audience of potential attendees)
    • Communication with focal points, such as faith leaders, about potential transmission events to raise awareness (‘warn and inform’)
    • For private social events, work from guest registration and booking lists
    • When necessary, consider media release specifying the event day and time, with a request for people to self-identify as a potential contact
  • Managing Contacts [1]
    • Contacts should ideally be contacted over the phone or in person, although alternative approaches such as text messages and emails could be considered when direct contact cannot be made.
    • Each contact should go in Quarantine for 14 days after the last contact
    • Daily monitoring:
      • Direct monitoring by the contact tracing team; monitoring potential signs and symptoms by phone or visiting them in person. Contact tracers should implement standard precautions and physical distancing.
      • Self-reporting, whereby contacts self-monitor and report any signs and symptoms to the contact tracing team. Self-reporting should be conducted daily, even if no signs or symptoms are present (so-called zero reporting).
      • Contact tracers collect information on signs and symptoms from each contact on a contact tracing form on a daily basis. Electronic data capture tools should be used wherever possible (see section on Information technology). Table 2 outlines the minimum information that should be captured on the contact tracing form.
      • If contacts cannot be reached, the contact tracing team should ask relatives and friends or explore other means to find them. If contacts relocate to known locations in the same catchment area, the contact tracing team should visit them. If contacts move to another catchment area, the contact tracing team responsible for that catchment areas should be informed and follow up.

Contact Tracing Apps

Some public health groups have developed Apps and other digital tools for Contact Tracing, some dating back to the SARS outbreak (2003). Here is an overview, followed by our usual observations, interpretations, and actions.

Overview of apps

  • TraceTogether, developed in Singapore, with recently all coding being published online for the common good. [2]
    • At the writing of this version of the page, over 62000 people have installed the app on their cellphone. For the app to start tracing, the Bluetooth setting on mobile phones has to be turned on. If a user gets infected, the authorities will be able to quickly find out the other users he has been in close contact with, allowing for easier identification of potential cases and helping curb the spread of the virus. [2]
  • Go.Data by GOARN: an outbreak investigation tool for field data collection during public health emergencies. The tool includes functionality for case investigation, contact follow-up, visualization of chains of transmission including secure data exchange and is designed for flexibility in the field, to adapt to the wide range of outbreak scenarios. The tool is targeted at any outbreak responder. [3]
  • WeTrace: Once a person logs in and uses the “WeTrace” app, it will trace his/her timeline and movements including the places he/she visited and the people who were with him/her on a particular timeline. The app does not ask for any personal/private data. What is visible is the individual’s unique ID number. [4]
  • Close Contact Detector: The 'close contact detector' tells users if they have been near a person who has been confirmed or suspected of having the virus. Once the new app is registered with a phone number, users are asked to enter their name and ID number. Every registered phone number can then be used to check the status of up to three ID numbers. [5]
  • Corona 100m: The Corona 100m (Co100) app, was launched on February 11 and, using government data, alerts users when they come within 100 meters of a location visited by an infected person. It had a million downloads in its first ten days after launch, according to South Korean government website, which said the app “allows users to conveniently avoid potentially dangerous locations without checking the travel histories of those infected”.[6]
  • CommCare: App that was used during the West Africa Ebola outbreak in Guinea. Built on the mobile application CommCare and business intelligence software Tableau, allows for real-time identification of contacts who have not been visited and strong accountability of contact tracers through timestamps and collection of GPS points with their surveillance data. [7]
    • Deployment of this system began in November 2014 in Conakry, Guinea, and was expanded to a total of 5 prefectures by April 2015. To date, the mobile system has not replaced the paper-based system in the 5 prefectures where the program is active. However, as of April 30, 2015, 210 contact tracers in the 5 prefectures were actively using the mobile system to collectively monitor 9,162 contacts. With proper training, some investment in technical hardware, and adequate managerial oversight, there is opportunity to improve access to surveillance data from difficult-to-reach communities in order to inform epidemic control strategies while strengthening health systems to reduce the risk of future disease outbreaks. [8]
Name Feature Developer Outbreaks Create tailored investigation form, chain of transmission, info can be adapted according to the diseases GOARN Ebola, Diphtheria
TraceTogether used to identify close contacts based on the proximity and duration of an encounter between the two users. Singapore Gov. and SGUnited Covid-19
WeTrace via mobile data, generates a unique QR code per user and traces their timeline, movements, locations, and even other users Department of Health, the Philippines Covid-19
Close contact detector indicate each person’s status: green for people who can leave their homes, yellow for people who need to quarantine themselves at home for seven days, and red for those who need to quarantine themselves at home for 14 days. The app tracks people’s movements. Having contact with people known to be infected or traveling to affected areas changes a person’s status. Only those with a status of green are allowed to enter businesses or to use public transportation or public facilities. China Covid-19
Corona 100m Not specific for contact tracing but informs citizens of known cases within 100 meters of where they are. South Korea Covid-19
CommCare App that was used during the West Africa Ebola outbreak in Guinea. DiMagi Ebola (Now offered for free for COVID19


  • Use of a mobile application for Ebola contact tracing and monitoring in northern Sierra Leone: a proof-of-concept study (Danquah et al, BMC, 2019): despite challenges, the study demonstrated that it was possible to implement mobile health (mHealth) in this emergency setting. [9]
    • The app had the benefits of improved data completeness, storage and accuracy, but the challenges of using an app in this setting and epidemic context were substantial. [9]
  • Oxford University provides evidence for coronavirus mobile app for instant contact tracing. [10]
    • The Oxford University team has provided European governments, including the UK, with evidence to support the feasibility of developing a contact tracing mobile app that is instant, could be widely deployed and should be implemented with appropriate ethical considerations. The Oxford University team recommends that the mobile application should form part of an integrated coronavirus control strategy that identifies infected people and their recent contacts using digital technology. [10]
    • Visit: for the science behind this work.

Analysis and interpretation

  • Anyone who has gone through the painstaking, frustrating process of contact tracing, encountering memory fallacies, wrong phone numbers or addresses, refusal to cooperate, must have thought: "If ever there is a time for Big Brother, it is now. Please help". Digital tools CAN help. Technically, it is no longer a big deal. The key issue popping up is privacy: a society value that varies in weight across the globe. In the EU, where the older generation still carries scars of a totalitarian regime that meticulously registered individual traits, in order to exterminate large groups based on that registry as a next step, you can imagine that the protection of the individual, personal data is paramount. Only a few weeks into the Coronavirus Pandemic, the Dutch parliament voted against the proposal of the EU to use mobile phone provider tracker data, to identify risk areas and populations at risk. [11]
  • Contact Tracing takes more than having tools (paper-based or digital) to find a risk contact. Then the hard work begins, communicating the risk to an individual, convincing them to cooperate, change behavior, change a way of living. So, it is not a one of contact: that too needs to be managed over time. You need to handle contact data in the same secure way as you handle case data. During outbreaks, a data manager is not a luxury but a necessity to have in any outbreak investigation team. For example, the WHO guideline on Ebola contact tracing (2015) describes this well. [12]
  • For COVID19, the mantra is Testing, Testing, Testing. Any registration support (paper or digital) for contact tracing needs to be combined with reliable testing of contacts and suspect cases.

Consequences for action

Comparing Contact Tracing in Europe


Comparing contact tracing protocols of EU countries with ECDC and WHO guidance:

Topic WHO Interim Guidelines (10 may) ECDC recommendaton (8 April) DE (4 may) NL (6 may)
Start infectious period COVID case 2 days before onset 48 hours before onset 2 days before onset 2 days before onset
End infectious period COVID case 14 days after onset 14 days after onset unknown 24 hour after symptoms disappear or "after at least 7 days since onset"
Start infectious period asymptomatic COVID 2 days before first positive sample 48 hours before first positive sample
End infectious period asymptomatic COVID 14 days after positive sample 14 days after positive sample
Face to face contact within 2 meters for > 15 minutes Risk (<1 meter > 15 mins) High risk High risk High risk (note: in NL the distance is 1.5 m)
Physical contact with COVID case Risk High risk High risk High risk
Unprotected, direct contact with secretions of COVID case Risk high risk High risk High risk
In same closed environment (e.g. Waiting Room) for more than 15 minutes Risk High Risk Medium risk Low risk
In same aircraft 2 seats removed from covid case Risk High risk High risk
HCW providing care to COVID without proper PPE Risk High risk High risk
Lab worker handling COVID samples without proper PPE Risk High risk High risk
Other high risk events Aerosol procedures
Face to face contact within 2 meters for <15 minutes Low risk
In same closed environment (e.g. Room) for <15 minutes Risk Low risk
Travelling with COVID case in any mode of transport Low risk
HCW providing care to COVID with proper PPE Low risk low risk No Risk
Source tracing Not mentioned No priority Identify possible source of infection:
Contact identification and listing Develop a contact list. Contact Each by phone or in person at first Immediately after confirmed or probable case was identified Immediately after confirmed or probable case was identified Immediately (<24 hrs) after confirmed (probable or suspect cases are not reported) case was identified
Follow up high risk contacts Active, Daily OR: by self-reporting WITH zero reporting Actively, daily Actively, daily Passive, via mail.
Follow up low risk contacts Self-monitoring Self-monitoring Self-monitoring
Contact definition Time, Place, Person Time, place person Time, place person Place, Person
Intervention high risk contacts 14 days quarantine (home) Stay at home, avoid contacts Household members of covid cases stay at home "as much as possible" for 14 days. Note: Children may go to school, and adults may leave the house for shopping (!)

Analysis and interpretation

Consequences for action


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Contact tracing in the context of COVID-19. Interim guidance 10 May 2020
  2. 2.0 2.1 Coronavirus: S'pore Government to make its contact-tracing app freely available to developers worldwide. PUBLISHED MAR 23, 2020, 5:58 PM SGT
  3. WHO. About Go.Data.
  4. Cebuano IT expert develops mobile app for COVID-19 contact tracing. Published March 23, 2020, 12:07 PM. By Minerva Newman. Manila Bulletin.
  5. China launches the coronavirus 'close contact detector' app. BBC News. 11 February 2020.
  6. South Korea to step-up online coronavirus tracking. News. 12 Mar 2020 by Sarah Wray: Editor, SmartCitiesWorld
  7. 3 Lessons from Contact Tracing During the Ebola Outbreak. Blog. DiMagi Website. March 7, 2016
  8. Sacks, Jilian A., et al. "Introduction of mobile health tools to support Ebola surveillance and contact tracing in Guinea." Global Health: Science and Practice 3.4 (2015): 646-659.
  9. 9.0 9.1 Danquah, Lisa O., et al. "Use of a mobile application for Ebola contact tracing and monitoring in northern Sierra Leone: a proof-of-concept study." BMC infectious diseases 19.1 (2019): 810.
  10. 10.0 10.1 OXFORD UNIVERSITY BIG DATA INSTITUTE. NEWS RELEASE 17-MAR-2020. Oxford University provide evidence for coronavirus mobile app for instant contact tracing
  11. REF
  12. EMERGENCY GUIDELINE. Implementation and management of contact tracing for Ebola virus disease. September 2015