Contact tracing for COVID-19

ECDC has provided contact tracing guidance, which should be considered together with the options for adapting quarantine and isolation when there is a high or extreme pressure on healthcare systems and other functions in society.

Contact tracing is a public health practice used to identify and notify people who have been exposed to someone with an infectious disease such measles, tuberculosis, syphilis, and HIV/AIDS. Contact tracing has been extensively used during the COVID-19 pandemic and other infectious disease outbreaks to support early diagnosis and interrupt onward transmission by rapidly identifying and managing any secondary cases that may arise following transmission from primary cases.

Principles of contact tracing

The aim of identifying and managing the contacts of COVID-19 cases is to support early diagnosis and interrupt onward transmission by rapidly identifying and managing any secondary cases that may arise following transmission from primary cases. This is achieved by:

• promptly identifying the contacts of a COVID-19 case;
• providing contacts with information on self-quarantine, proper hand hygiene and respiratory etiquette, and advice on what to do if they develop symptoms;
• testing all contacts who have had high-risk exposure to COVID-19 cases, whether or not they are symptomatic, as soon as possible after they have been identified, to allow for further contact tracing;
• testing all contacts who have had low-risk exposure to COVID-19 cases in settings where transmission is likely and/or the population is vulnerable to severe COVID-19;
• testing all contacts that become symptomatic.

Contact tracing is a key tool for breaking transmission chains. For countries with high transmission, contact tracing will complement other measures, such as physical distancing, and help reduce transmission. For countries with lower levels of transmission, contact tracing is the key to outbreak management and control of transmission.

For contact tracing to be effective it needs to be prompt. This includes testing cases as soon as possible after symptom onset – which requires a high level of public awareness and easy access to testing. Test turnaround time should be minimised, and contacts traced as soon as possible after a positive result. While awaiting the results of their test, those who are symptomatic can be encouraged to inform their close contacts and suggest to them that they adhere to physical distancing measures until the result is known.

Additional information on different settings can be found below.

Monitoring

ECDC and WHO encourage countries to monitor the effectiveness of their contact tracing operations in order to identify where coverage or timeliness needs to be improved (See ECDC’s publication Monitoring and evaluation framework for COVID-19 response activities in the EU/EEA and the UK). To learn more about the transmissibility and characteristics of VOCs, countries are encouraged to collect and analyse contact tracing data from these cases and to share findings with ECDC, WHO and other EU/EEA countries.

Data collection

The TESSy reporting protocol describes the collection of data regarding contact tracing. The data collection aims to help assess the effectiveness and efficiency of contact tracing operations, to provide information on transmission of SARS-CoV-2, and to provide contextual information on the progression of the pandemic to tailor response measures.

An example of analysis of contact tracing data in three countries (Italy, Ireland and Spain) can be found in this report. The report describes the main challenges that arose during this analysis and how these challenges were overcome, and also suggestions for best practice.

Mobile apps

Countries using mobile apps for contact tracing are also encouraged to refer to ECDC’s guidance on mobile apps in support of contact tracing and to monitor their effectiveness using the joint WHO-ECDC indicator framework.

With regard to VOCs, countries are encouraged to monitor the number of contacts testing positive of those notified, or apply similar measures in order to understand whether the parameter settings need calibration – e.g. due to a more transmissible variant. ECDC’s guidance on mobile apps has further details on evaluating and calibrating settings.

International collaboration 

When contact tracing investigations identify contacts or a potential source in another country, public health authorities should collaborate across borders and exchange data in a secure way (through, for example, the selective exchange messaging function of the Early Warning and Response System (EWRS) of the European Union or share data using the European Digital Passenger Locator Form).

Passenger Locator Forms

On 27 May 2021, the European Commission published the Implementing Decision 2021/858 outlining the function of the digital Passenger Locator Form (dPLF) in the EU/EEA.

Documents on contact tracing, including those related to special settings or populations