Coronavirus: contact tracing explained

A government worker demonstrates Singapore’s contact-tracing smartphone app. Photograph: Catherine Lai/AFP via Getty Images

WHO says Covid-19 patient tracing should be ‘backbone of the response’

What is contact tracing?
This is one of the most basic planks of public health responses to a pandemic. It means literally tracking down anyone that somebody with an infection may have had contact with in the days before they became ill.
It was – and always will be – central to the fight against Ebola, for instance. In west Africa in 2014/15, there were large teams of people who would trace relatives and knock on the doors of neighbours and friends to find anyone who might have become infected by touching the sick person.
Is it harder to do in the case of a respiratory infection?
Most people who get Covid-19 will be infected by their friends, neighbours, family or work colleagues, so they will be first on the list. It is not likely anyone will get infected by someone they do not know, passing on the street.
It is still assumed there has to be reasonable exposure – originally experts said people would need to be together for 15 minutes, less than 2 metres apart. So the contact tracer will want to know who the person testing positive met and talked to over the two or three days before they developed symptoms and went into isolation.
What do the contact tracers do then?
In the way it was operating in February, the tracer would call the contacts and ask them how close they had been to the person with symptoms and establish whether they were low-risk or high-risk. If the latter, they would be asked to isolate themselves for 14 days at home.
The contact tracers would either call each day to check how they were or ask them to phone if they felt ill. If they developed symptoms, the tracers would start again, looking for their contacts in turn.
Who does the contact tracing?
It is organised by Public Health England, which had 290 staff doing it before community testing stopped in mid-March. Public health in recent years has been the responsibility of local government, so any increase in contact tracers might come from councils.
Which other countries have done this to scale?
South Korea has large teams of contact tracers and notably chased down all the contacts of a religious group, many of whose members fell ill. That outbreak was efficiently stamped out by contact tracing and quarantine.
Singapore and Hong Kong have also espoused testing and contact tracing and so has Germany. All those countries have had relatively low death rates so far. The World Health Organization says it should be the “backbone of the response” in every country.

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