Dr Helen Dodson
- May 27, 2020
- 5 min read

Track and Trace.

As the UK begins to ease its lockdown we are hearing more about the programme of “Track and Trace” that will be implemented in an attempt to keep COVID-19 under control.

Contact Tracing.

Usually referred to as “Contact Tracing”, this is not a new concept in infectious disease control. It is common practice in many countries, including the UK, to try and control the outbreak of infectious diseases by finding who has been in contact with the sufferer and treating and/or isolating them.

In the UK this is routinely carried out in cases of sexually transmitted infections and notifiable infections such as measles and tuberculosis. (1) (2)

Done quickly, contact tracing can help contain disease outbreaks and stop more widespread infections.

At the beginning of the COVID-19 outbreak in the UK contact tracing was being carried out. However as numbers of cases rapidly rose this was abandoned on 12 March 2020 when it could no longer keep up with the pace of infections.

How does it work?

When a person has been diagnosed with an infectious disease they may have transmitted to others they are asked about all their recent contacts.

For sexually transmitted diseases this means only sexual partners need to be traced and for diseases such as measles or tuberculosis the number of close contacts is usually relatively small and localised to one area of the country.

Once traced, the contacts are telephoned and the necessary advice and/or treatment organised. Public health can usually cope with these scenarios because at any one time the numbers involved are very small. This method is referred to as manual tracing.

It is laborious work as the patient has to remember all their recent contacts, give their details to public health staff who then in turn contact each individual on a one-to-one basis. Each call takes around 15 minutes and is done confidentially. The information is not shared with anyone, not even the person’s GP.

With COVID-19 the combination of a highly infectious virus and the fact is it widespread throughout the country means the whole process of contact tracing has to be scaled up to levels beyond the usual capacity.

What is the Definition of a Contact in COVID-19?

The European Centre for Disease Prevention defines a high risk contact as someone who has been within two metres of a COVID-19 infected person for at least 15 minutes.

Low risk is defined as contact of less than 15 minutes and/or at more than a two metre distance. There is therefore some variation within these definitions and ideally each case needs individual assessment.

For example, face to face exposure with an infected individual at less than two metres distance and for less than 15 minutes is classed as low risk but if the same scenario lasted for 20 minutes it becomes a high risk situation. The 15 minute cut off has been set for practical reasons to guide practice. The two metre distance is based on how far droplets spread when a person coughs or sneezes but studies have shown that some droplets travel further than this. It is important to remember that being classed as “low risk” does not equate with “no risk”. (3) (4)

South Korea has been seen as the exemplar model of contact tracing. However some of its effectiveness was down to other methods that were used such as examining CCTV footage, and analysing mobile phone GPS data and credit card transactions to find contacts of an infected individual. These sorts of measures work extremely well but would not be tolerated in many other countries. (5)

What is the Smartphone App?

Here in the UK smartphone users will be encouraged to download an NHS app that will have several uses. Firstly, it can be used to report any symptoms of COVID-19 the user may have and the app will explain where and how to get a COVID-19 test. Secondly, if the test is positive, the onus is on the person to notify the app which will then identify and notify the owners of other phones that were nearby by sending an alert to their phones.

At the time of writing it is not clear how far back in time the app will “look” for contacts. The software is equipped to differentiate between different levels of contact risk so in theory, the person sat next to an infected person on the bus for 30 minutes should receive an alert, but not the person they passed in the street for a matter of seconds.

Manual tracing has better results in terms of reducing disease transmission. The Centre for the Mathematical Modelling of Infectious Diseases compared manual and app contact tracing models and found that manual tracing was 61% effective compared to 44% for app tracing. However the app method is much more efficient in terms of manpower. The mathematicians made an assumption that 53% of the population would download the app in arriving at their figures and this highlights what could be one of the main problems with the app, it will only work if enough people download it and use it. It will require around 80% of people who own a smartphone to download it which in turn represents 56% of the total UK population. (6) (7)

The reality is that both methods of contact tracing will be needed, manual and app, and an estimated 25,000 people have been recruited to handle the manual aspect. The government had expected the whole system to be up and running by 1 June 2020, just five days away at the time of writing. Instead the manual tracing scheme starts tomorrow (28 May) with no date for the app announced yet. (8)

Possible Problems.

The NHS app was trialled on the Isle of Wight and encountered various technical problems, not least that it did not work well with Google and Apple operated phones which make up a substantial part of the mobile phone market. (9)

Contact tracing also works on the good will of the people contacted who are asked to self-isolate for 14 days because they have been in the vicinity of a person with COVID-19 and are now deemed "high risk". As people go back to work, and with so many businesses on the brink of economic collapse as a result of the lockdown, people may not want to lose another two weeks’ of earnings.

The UK COVID-19 contact tracing is a centralised scheme, meaning that all the data goes to a central base. Some public health doctors have suggested that the system would work better if run locally within the community as has been done in the past with other infectious diseases.

Professor Allyson Pollock, Clinical Professor of Public Health at Newcastle University, has said that “local teams would be able to decide for themselves how to deploy contact tracers because they have a clear understanding of what parts of the local community are most vulnerable.” (10)

Concerns around civil liberties and the track and trace scheme have also been raised. Although the Health Secretary, Matt Hancock, has said all the data would remain anonymous and would be deleted after 28 days, Michael Veale, a lecturer in Digital Rights and Regulation at University College London, has pointed out that the way in which the app anonymises data does not even meet the UK legal definition of anonymisation and there are concerns that it will be possible to trace the data back to individuals through their NHS records. (11)

In Conclusion.

To be able to come out of lockdown successfully, the UK needs to have robust methods of identifying further COVID-19 outbreaks. Tracing the contacts of known cases is a vital cornerstone in that process and is the way many other disease outbreaks are already handled in the UK. Although there are justifiable concerns about data protection and civil liberties with the rolling out of a nationwide track and trace scheme, the reality is that without the ability to closely monitor and respond to ongoing cases of infection, the UK would need to remain in a restrictive lockdown for much longer.