Bringing contact tracing home: household changes enable a more accurate picture of performance

Much of the criticism regarding the NHS Test & Trace system has focused on its effectiveness in reaching people who have come into close contact with those who have tested positive for Covid-19. A superficial glance at the statistics leads to the perception that between 30-40% of these people have not been reached. However, as the detail of the official NHS Test & Trace tables themselves shows, this isn’t the real picture.

Digging a little deeper into the official Excel data files you find, arguably, the most striking statistic of the tracing data – 75-80% of close contacts not reached by the central system actually live in the same household as someone who has tested positive and who has already been made aware of their diagnosis.

But why does this matter? Well, this means that 75-80% of the people who are reportedly not reached are in fact in the same house as someone who has tested positive, already been reached, and been told to self-isolate by NHS Test and Trace. These people are therefore likely to be already well aware that they have come into contact with someone who has tested positive, and if this 75-80% are already following the widely-understood guidance and self-isolating, this means that in fact 90-95% of people who genuinely need to hear from the central tracing system do so.

Other UK jurisdictions, for example Wales, have, since the start, in some cases counted as reached individuals in a household when only one member has been contacted.  The Scottish system has a lower threshold again for defining someone as reached – with an SMS text message being sent to the individual enough to qualify.  This is unlike the English system where a person has only been counted as reached if they themselves respond to online or telephone communications with a tracer.

Who are these people in a household that should now be counted reached? In large part it is likely to be the family of the person who has tested positive, including children. Until now, the need to contact every individual led to the unusual statistical requirement of a tracer only being able to say a child who lives in the same household as their positive-tested parent was reached if the tracer spoke directly to the child – be they toddlers, tots or teens.

For example, a parent tests positive, is told to self-isolate and is asked to identify people they have been in close contact with. Quite rightly they identify their 5-year-old child who lives in the same house.  If that child was not directly spoken to by a contact tracer, they were counted as ‘not reached’, even though the parent will have been given the necessary information and the household is following the guidance to isolate.

This change is not about a statistical tweak, but an improvement to the service for people who come into contact with it.  It means that households will not now feel pestered by multiple repeat calls to its different members as tracers seek to speak to children to ensure they can be counted as ‘reached’. 

In a system where public goodwill towards this service is paramount to success and compliance, this improvement to the citizen experience should also reap wider rewards not just for families, but also public health.

Finally, it means the tracers and system can be more efficient, reducing the time they spend on repeat calls to households, and instead focussing on those harder to reach and genuinely new and separate cases.

In addition to this recent change relating to children, further improvements on how households are contacted look to be on the horizon. For example, adults sharing a household could also be, where appropriate, traced through a single telephone call to the household. To continue the above illustration, this means, if a household is made up of two parents and 5-year-old child and one parent tests positive, the whole household could be reached by speaking to one parent who can confirm the isolation of the entire family. 

This could be further enhanced if multiple close contacts who share a household, but do not live with the original positive case, could also be contacted on a household-by-household basis.

The changes we have now seen in relation to the tracing of under 18s is a sensible step. With further improvements on the horizon for tracing over 18s in a similar fashion, the accuracy of the picture of how NHS Test & Trace is - and has been - operating is likely to continue to improve. This will also ensure a more efficient service for the public.

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