The importance of test and trace: solutions from the private sector
Lockdown is not sustainable, mentally, physically and financially. We must plan to live with covid-19 circulating. At the start of the outbreak, we were racing against a threat with so many unknowns. Due to an unprecedented volume and speed of international research, we now know so much more about the virus (and have more of an idea about the known unknowns). Therefore, as we emerge past the (?first) peak of covid-19, we can devise evidence-based strategies to re-open society whilst the very real risk of infection is present. Crucially, to suppress transmission, we must rapidly detect and isolate new cases and their contacts: effective test and trace must be a cornerstone of any successful policy. Unfortunately, the process in the UK has been less than smooth. Here we outline the importance of test and trace and potential solutions offered by the private sector.
Lifting lockdown, R and the importance of testing
Modelling1 suggests that removing covid-19 restrictions too quickly and having to re-introduce lockdowns will be worse for the global economy than a more gradual approach. There is a delicate balance: the health effects of economic destruction are huge, but the virus has not disappeared and we still have a large proportion of the population that is vulnerable to infection and onward transmission. The R number we have heard so much about teeters around 1 (nationally, though there are regional variations). There are understandable concerns that relaxing the lockdown will lead to a rise above this and therefore a re-start of exponential growth of infections and a second peak or wave. Indeed, countries that have relaxed measures before us have seen local outbreaks.
To prevent these outbreaks and manage them early, it is crucial to rapidly identify and isolate new cases of covid-19. This is where the government “test and trace” system2 comes in. It aims to test and isolate all symptomatic individuals. Their contacts will be traced and isolated as well. In this way (in theory), chains of transmission are broken.
Test and trace
The test and trace programme for covid-19 is based on the contact tracing system used in Public Health for decades. The idea is to identify infectious individuals and isolate (and treat if there is a treatment). The individual’s contacts are traced and these individuals are isolated and/or treated. The system has been successful and is well established for these communicable diseases. However, covid-19 is a different entity and there are several potential stumbling blocks.
Asymptomatic spread
We know that individuals with covid-19 can spread disease asymptomatically. Therefore testing only symptomatic people will miss these silent spreaders. Of course, if the asymptomatic carrier is a contact of a symptomatic individual, we hope the test and trace system will identify them. We also know that individuals spread covid-19 pre-symptomatically, possibly 2-3 days before symptom-onset. Therefore, contact tracing must go back to the time before symptom-onset: will individuals remember all of their contacts when they were not on high alert to mentally document this?
Some institutions are swabbing staff regularly to identify asymptomatic carriers. Indeed Imperial College modelling suggests that weekly screening of healthcare workers by PCR would reduce onwards transmission by a further 16-23% on top of self-isolation based on symptoms if results were available at 24 hours3.
Accuracy of the test and test result interpretation
The test results for covid-19 should be interpreted within their clinical context considering the accuracy of the rest and the pre-test probability (estimated risk of the disease before testing). These same principles hold for all other medical tests- they should be performed by someone who is able to explain the results and interpret them appropriately.
However, with test and trace, individuals are able to gain access to tests and follow an algorithm for the outcome. Of course, this is because of the vast numbers of tests likely to be performed. But the risk of misinterpretation and incorrect action is huge.
The PCR test is highly specific, which means that the rate of false positives is low. However, there are big doubts over the sensitivity of the test- the false negative rate is up to 30%. Many of the tests are self-tests (even at the drive-through centres, people are asked to test themselves): we know this raises the probability of a false negative due to poor technique.
Yet the test and trace programme actions negative results by allowing individuals and their households out of isolation and back to work. Contacts are not traced. With a 30% (and possibly) higher false negative rate, that is extremely worrying. False reassurance would enable people to continue to spread covid-19.
What can we do to mitigate this? Hopefully new tests will be developed which are less operator-dependent (e.g. salivary tests that provide rapid results) with greater sensitivity. Having access to clinical advice is important: the results should be reviewed in clinical context. If someone has a high pre-test probability (classic symptoms and signs), a negative result should be viewed with caution.
Tracing
According to the new test and trace system, there are multiple steps each with their own time-delay. Expedience is crucial as we need to track cases as quickly as possible to reduce spread, particularly as people are most infectious around the time of symptom onset.
The steps are as follows:
- Index case has symptoms
- Case applies for a test
- Test performed
- Results received
- If positive, contact tracing begins
- Contacts isolated for 14 days
As you can see, there are many steps to this process, each with potential pitfalls and delays. Time is critical- to reduce spread this needs to be as rapid and frictionless as possible.
For the government system, the tracing process begins once a positive result is received rather than when a person has symptoms. If there is a significant time delay from symptoms-test-result-trace, this leaves a number of potential spreaders to transmit disease. Therefore places where outbreaks are likely e.g. office environments need to ensure their systems are honed and efficient: employees must be able to access tests and results quickly. At the moment, that process is too slow- publicly accessed tests can return results at 48hrs if not longer.
The contact tracing that follows must also be rapid: experts agree that in order for contact tracing to work, it has to be fast. Indeed, Professor Mark Woolhouse, from the Infectious Disease Epidemiology department at the University of Edinburgh states that speed is actually more important than making sure to track down every last contact.
At present, the much-lauded (but subsequently highly questioned) contact-tracing system is manual (though an app is planned for release), which will again add in a delay. But will people even comply with the process?
For example, in a pilot study in Sheffield, set up by a group of retired doctors and public health officials, only one-third of people identified as contacts agreed to self-isolate. There are also concerns about actually making contact- tracing efforts were paused in Washington State after many simply did not answer the phone to an unknown number.
In the UK, for data protection reasons, tracers will not be able to provide much information about where and when an individual might have been exposed. This is may well affect compliance.
Another huge issue is remembering significant interactions, which affects how many contacts can actually be traced. In normal life, according to Dr McLachlan at Queen Mary University, London, it is estimated the average person will only remember around 35% of their daily interactions.
This is why leveraging technology via, say, an app is so important. Of course, uptake and involvement has to be high to be of any use and the technology has to be good enough to be worthwhile.
How can we optimise this process?
We can target every stage of the symptoms-test-result-trace process to ensure that it is as efficient and effective as possible. Again, speed is one of the most important factors here.
The most accurate tests should be provided rapidly with very quick turnaround times to ensure potential cases are isolated as quickly as possible. Discussing cases with clinical teams in order to evaluate the results in clinical context will be very useful to mitigate against sensitivity issues. Effective contact tracing should be rapid in order to isolate all significant contacts quickly.
An efficient contact tracing system should leverage technology but this is not happening in the UK at present and the proposed solutions are less than ideal.
The UK government are planning to deploy a mobile-based bluetooth solution. It is currently being trialled in the Isle of Wight with no set release date. Already, it has been fraught with problems some which include:
- Mobile based bluetooth solution
- Issues with mobile variations (devices react differently to applications working in background and can stop them from working)
- Inaccurate distance measuring (devices can't measure the distance from each other accurately creating a large error in measurement) which could cause flagging of false positives
- Requires 60-70% of population to adapt, which is difficult with a whole country
- Data collected is currently centralised
- Application frequency of operation in background is unreliable due to the device variation (can be 15minutes for every scan cycle - issues arise especially with iPhone devices)
- Affects devices battery life
- Requires the person to have their phone on them at all times.
In response to these issues, private companies are creating more efficient and effective solutions to allow localised accurate, thorough and rapid contact tracing in, for example, office environments. Alongside clinical services, we can offer a solution that allows companies to quickly and reliably react to a positive result (or symptoms). This product is a standalone wearable device, which stays attached to employees, guests and contractors. It does not suffer issues associated with mobile devices such as battery life and integration with different operating systems. As it is wearable, it can stay on for the duration inside offices rather than missing important contacts if phones are separated from a person. Importantly, it has improved indoor accuracy compared with other solutions and measures distance accurately. Concerns about data collection are accounted for: the data is completely anonymous and decentralised. No medical data is stored. Overall, it gives a rapid method to identify significant contacts rapidly (may of which an individual may not recall) enabling effective tracing and localised action, preventing lockdowns of whole buildings.
Employers have a duty to make their workplaces as safe as possible.This will involve changes to the environment and behaviour alongside a robust clinically managed testing and tracing programme. Although this may seem disruptive for businesses, it is less disruptive than an outbreak of COVID-19 in the workplace will be.
1. https://www.nature.com/articles/s41562-020-0896-8
3. https://www.imperial.ac.uk/media/imperial-college/medicine/mrc-gida/2020-04-23-COVID19-Report-16.pdf