TThe constant flow of people in the two surge test units in Finchley, north London, last week suggests that, more than a year after the outbreak of the pandemic, the public spirit to do something about it Covid is still strong.
The effectiveness of surge testing is, however, a more open question. The rapid test of 5,000 households last week was an attempt to isolate the South African variant and other sources of concern. Yet although standard PCR tests return within 24 hours, genomic sequencing tests to identify a variant of Covid take 14 days – by which time the period of infectivity is usually over.
Speaking with folks in North London, it was clear that public awareness of the distinction between regular testing and surge testing was not always evident, despite the strong desire to help.
“There’s been something here – they’re having a push from the South African variant,” Avril Endfield said on Friday, before taking one of the tests offered in the black tent outside Tesco. “I received a vaccine and I have another in 10 days. My daughter is about to give birth and I really wish I could see her. Hope this helps me do it. “
Rino Sampieri’s motivation for testing was similar. “I have been semi-armored for my mother and I am on flexible leave,” he said. “I have no symptoms and don’t think I have it, but… anything to get the economy back on its feet.”
Barnet’s board was doing a surge test due to evidence that a person in the Finchley postcode area had the South African variant. Existing vaccines are currently less effective against it and may spread more easily than others.
Dozens of regions around England have been subjected to surge tests since February. Most, like Finchley’s test, only involve one or two confirmed cases, and so far none of the variants have spread.
But public health officials were concerned last week when 44 cases were identified in the boroughs of Lambeth and Wandsworth in south London, along with 30 other suspects, triggering a massive spate of localized testing. The Finchley case is unrelated.
Barnet has set up two mobile testing units and sent a team of seven door-to-door to distribute kits, which are used at home and then returned the next day. About 5,000 kits have been distributed and 80% have been returned.
Despite the 14-day delay, the surge tests were still helpful, said Dr Tamara Djuretic, director of public health at Barnet. “There is no better way to do it, and the important thing is that we still contain the infection and you treat them as if they are all a variant,” she said. “Once you start looking in this area, everyone becomes more aware that something is going on and that their behavior is changing. “
This is the third surge test performed by Barnet. The first, of around 10,000 people in East Finchley and Hendon at the end of February, found no variants of concern. “It was good, because it was opportunistic testing and we found positive cases that would not have been discovered otherwise,” Djuretic said. But it seemed that the variant had not spread.
The second test, at Muswell Hill, looked for possible transmission of the Brazilian variant from someone who arrived in the UK. “We have found evidence of transmission of the variant in a few households,” she said. “It was during the first lockdown, so the contact was pretty limited.”
The surge test is “an important tool in the arsenal of public health,” according to Jim McManus, vice president of the Association of Directors of Public Health.
“You can’t expect residents to do this all the time,” he said. “You have to discern when it’s worth it.” He said he was “frankly amazed” by the heavy use of surge testing. “Our efforts with the South African variant are always focused on containment,” he said. “Surge testing can be extremely useful when you believe there is a possibility of community spread and you are having difficulty contacting-tracing people beyond the immediate network of contacts.
A third technique used by a number of public health officials is network analysis. When an infected person talks to contact tracers, they give out information about where they have traveled, and analysts will look for cases where zip codes overlap, to try to find how a virus has spread.
“It takes time, but it definitely produces results,” said McManus. “We found one person who was moving to three different offices in a company, who was the common factor in the spread of the virus.”
Allowing people to self-isolate was always crucial, he said. And surge testing and tracking variants using wastewater analysis are both useful, but they also rely on genomic sequencing. “Our ability to do genome sequencing in this country is by far one of the best in the world,” he said. “But it is taking too long and needs to be speeded up.”