MUCH attention in the UK was last week focused on whether the country could meet its end-of April target of conducting 100,000 tests for coronavirus a day. While increasing testing capacity is important for countries that failed to contain the virus and now have massive outbreaks, how testing is used is even more important than how many tests are done.
To reduce the spread of the virus, many researchers think countries need to move to testing those without any signs of disease instead of focusing on those with symptoms.
“A good strategy would be to devote part of the resources for identifying asymptomatic infected too, starting with random testing in the population,” says Giulia Giordano at the University of Trento in Italy. People with mild symptoms can be isolated without wasting a test that could be instead used for identifying hidden outbreaks, she says.
Early on, most countries tested any individuals suspected to be infected. Anyone these people had come into contact with was then traced, isolated or quarantined, and tested too. But only a few countries such as South Korea managed to scale up this approach fast enough to keep pace with the outbreak. It works: on 30 April, South Korea reported no new infections within the country.
Many other countries, including the US and UK, failed to keep up with testing and contact tracing as their national outbreaks took off. Testing has instead been mainly restricted to use in hospitals to confirm that seriously ill patients have covid-19.
The UK government decided to limit testing to hospitals early in March. Critics denounced this as a blunder, arguing that more widespread testing was essential to being able to ease lockdown restrictions. The UK has since begun increasing testing and has announced plans to resume contact tracing.
“All the countries are stepping up their capacities to test,” says Francesca Colombo at the Organisation for Economic Co-operation and Development (OECD), and one of the authors of a report published last month on how testing can help lift restrictions. “Testing is going to be a key intervention as part of an exit strategy,” she says. “It is one element but a very important one.” Other elements include contact tracing and some continued social distancing measures to limit spread.
In countries with large outbreaks and limited testing capacity, the OECD report calls for testing to be extended to healthcare workers before being used as part of contact tracing. Where little contact tracing is being done, testing could instead be extended to key workers who come into contact with lots of people, such as those working in supermarkets, public transport and in delivery services.
The UK is now offering testing to healthcare workers, care home staff and residents, plus people who are over 65 or who have to leave home to work, and those they live with. But rather than offering testing to key workers who want it, the OECD recommends a strategy of regular testing of people in these groups, regardless of whether they have symptoms.
This is because people who think they may be infected should already be isolating themselves at home anyway. Testing such people would only help reduce the virus's spread if it were followed up by tracing and informing anyone they had been in contact with, something that many countries, including the UK, haven't yet resumed.
However, testing regardless of symptoms can identify people who don't realise they are infected because they don't have obvious symptoms or have only just been infected. Immediately isolating these people can then prevent further infections.
The issue is that people can be infectious for several days before showing symptoms, says Martin Hibberd at the London School of Hygiene & Tropical Medicine. “Getting tested once a week would be a good strategy,” he says.
Modelling by Nicholas Grassly at Imperial College London and his colleagues backs the idea of weekly screening of healthcare workers irrespective of symptoms. If the weekly test were done at the end of a shift and people told if they need to self-isolate before the start of their next shift, the analysis suggests that this could reduce the risk of them spreading the coronavirus by up to 33 per cent.
Weekly testing of the 35,000 people working in intensive care in the UK would require just 5000 tests a day. However, regular screening of all healthcare workers would require about 170,000 tests per day. On 3 May, 62,956 people in the UK were tested. Ideally, all those working in care homes or who care for vulnerable people should be screened weekly too.
For some, the idea of gradually extending weekly screening to healthcare workers and then to other essential workers isn't radical enough. To end the lockdowns quickly, the aim should be to test every single person once a week, says Julian Peto at the London School of Hygiene & Tropical Medicine.
“It's certainly feasible,” he says. “Everybody just takes it for granted that this is impossible.”
In a 17 April letter to The Lancet, Peto and others called for universal weekly screening to be trialled in a small town.