COVID-19 testing

"The textbook version of contact-tracing starts with someone testing positive for COVID-19 and isolating themselves. A contact-tracer interviews this person to find out who they might have exposed while infected, usually from 48 hours before the positive test, or before symptoms appeared (if there were any). Close contacts — those who’ve spent more than 15 minutes close to the infected person — are of special interest, but anyone who shared public transport or an office space might qualify. Tracers then call or visit those contacts to tell them they need to quarantine, so that they don’t pass the virus on to more people. The chain of transmission is broken. In reality, failures occur at every stage of this test–trace–isolate sequence. People get COVID-19 and don’t know it, or delay getting tested. Positive results can take days to be confirmed. Not everyone who tests positive isolates when requested; one survey in May found that in the United Kingdom, 61% of people who were self-isolating said they’d left their house in the past day. People can’t always be reached for an interview or don’t provide details of their close contacts. And not all contacts are reached, or are willing to comply with quarantine orders."

"The United States is in a particularly dire situation. “Public-health authorities are struggling to reach cases and contacts” despite aggressive efforts, says John Oeltmann, head of contact-tracing assessment at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. He and his team evaluated two counties in North Carolina. In June and July, 48% of cases in one county and 35% in the other reported no contacts. Of the contacts whose details were provided, one-quarter in one county and almost half in the other couldn’t be reached on the phone after three attempts over consecutive days. In New Jersey, just 49% of cases between July and November were contacted; only 31% of those provided any contact details. “These results are not rare,” says Oeltmann."

"In South Korea, authorities use data-surveillance techniques to get around the problem of people being unwilling to disclose — or unable to recall — close contacts. “We need to double-check,” says Daejoong Lee at the South Korean Ministry of Economy and Finance. A law passed in response to an outbreak of Middle East respiratory syndrome (MERS) in 2015 allows authorities to use data from credit cards, mobile phones and closed-circuit television to trace a person’s movements and identify others they might have exposed to the virus. Information about cases is published online, an approach that allowed the country to avoid broad lockdowns and “worked very well”, says Lee. Still, in March, the Korea Centers for Disease Control issued guidelines limiting the release of ‘excessive’ information, after regional governments published maps of infected people’s routes in too much detail. In one case, a person was wrongly accused of having an affair with his sister-in-law because their overlapping maps revealed they dined together at a restaurant. Tracers in Vietnam also use extra data — such as Facebook or Instagram posts and mobile-phone location data — to check a person’s movements against those reported to contact-tracers. But the country’s success was down to “the boots on the ground”, says Todd Pollack, an infectious-disease specialist at the Partnership for Health Advancement in Vietnam, a collaboration that provides training and support for the nation’s health system. Contact-tracers interview people face-to-face and use the extra surveillance data to prod for more details."

"The WHO’s benchmark for a successful COVID-19 contact-tracing operation is to trace and quarantine 80% of close contacts within 3 days of a case being confirmed — a goal few countries achieve. But even that’s not quick enough, says Christophe Fraser, a mathematical biologist at the University of Oxford, UK. Transmission is too rapid and the virus can spread before symptoms emerge, he points out. Modelling by Fraser and his team suggests that even if all cases isolate and all contacts are found and quarantined within three days, the epidemic will continue to grow. He says that in a single day, 70% of cases need to isolate and 70% of contacts need to be traced and quarantined for the outbreak to slow (defined as each infected person passing the virus to fewer than one other, on average). But there are ways that contact-tracers can get ahead of a rapidly spreading outbreak. One is to cast a wider net around each case, so that second-order contacts — ‘contacts of contacts’ — are traced and quarantined; in Vietnam, tracers sometimes reached out to third-order contacts if a case was identified late in its infectious cycle. As many as 200 contacts for each case are found and tested, says Pham Quang Thai, an epidemiologist at the National Institute of Hygiene and Epidemiology in Hanoi, who leads the national contact-tracing taskforce. “If we want to run as fast as the virus, we have to chase not only the first round,” he says."

"Another useful strategy is to trace a new case’s contacts as far back as a fortnight before they caught the virus, to identify who infected them. This ‘backwards contact tracing’ is extremely effective for the coronavirus because of its propensity to be passed on in superspreading events, says Adam Kucharski, an infectious-diseases modeller at the London School of Hygiene & Tropical Medicine. One study in Hong Kong found that 19% of cases of COVID-19 were responsible for 80% of transmission, and 69% of cases didn’t transmit the virus to anyone."

"For some US allies, the fixation on words at a time when the international order was arguably facing its greatest challenge since the second world war encapsulated the glaring absence of US leadership. And that absence was illustrated just as vividly by news coverage of planes full of medical supplies from China arriving in Italy, at a time when the US was quietly flying in half a million Italian-made diagnostic swabs for use in its own under-equipped health system and Donald Trump was on the phone to the South Korean president pressing him to send test kits."

"A survey of attitudes to contact-tracing across 19 countries in August found that nearly three-quarters of respondents would be willing to provide contact information. But rates varied. In Vietnam, only 4% of participants said that they wouldn’t provide this information. In the United States and Germany, the proportion was 21%, and in France, it was 25%. Concerns around data privacy and tracking are partly to blame, says researcher Sarah Jones at Imperial College London, who co-led the survey. “Many health authorities and governments, especially in North America and Western Europe, may need to urgently improve public-health messaging to mitigate concerns about contact-tracing,” she says. “Public trust in all sorts of institutions is declining,” says sociologist Robert Groves, former director of the US Census Bureau, who notes that this is especially the case in large urban areas where social cohesion has also declined. But the low numbers of people providing details of contacts or responding to calls from contact-tracers, while disappointing, are not surprising, says Mary Bassett, a public-health researcher at Harvard University in Cambridge, Massachusetts. Some communities that have been hardest hit by COVID-19 have a long-standing distrust of public-health authorities, she says. “For the African American community, there’s a history of malfeasance on the part of the public-health system,” she says, “and for the Latino community, there’s a problem of members of the community who are undocumented” — and fear deportation.” Systems are often hampered by a lack of support for people who fall ill or need to quarantine, too. Providing adequate financial compensation for personal hardship as a result of quarantine could shift people’s reluctance to comply. The prospect of being without income for two weeks — or losing a job entirely — is a big burden, says Plescia, and might explain people’s reluctance to provide details for their close contacts."

"As the number of UK coronavirus cases surged in early 2021, the government announced a potential game-changer in the fight against COVID-19: millions of cheap, rapid virus tests. On 10 January, it said it would roll these tests out across the country, to be taken by people even if they have no symptoms. Similar tests will play a crucial part in US President Joe Biden’s plans to tame the raging outbreak in the United States. These speedy tests, which typically mix nasal or throat swabs with liquid on a paper strip to return results within half an hour, are thought of as tests of infectiousness, not of infection. They can detect only high viral loads, so they will miss many people with lower levels of the SARS-CoV-2 virus. But the hope is that they will help to curb the pandemic by quickly identifying the most contagious people, who might otherwise unknowingly pass on the virus. Yet, as the government announced its plan, a furious argument broke out. Some scientists were delighted by the United Kingdom’s testing strategy. Others said that the tests would miss so many infections that, if rolled out in their millions, they could cause more harm than good. Many people might be falsely reassured by a negative test result and change their behaviour, argued Jon Deeks, who specializes in test evaluation at the University of Birmingham, UK. And, he said, the tests would miss even more infections if people self-administered them, rather than relying on trained professionals. He and his Birmingham colleague Jac Dinnes are among scientists who want more data on rapid coronavirus tests before they’re used widely. But other researchers soon fired back, saying that the claim that the tests could cause harm was wrong and “irresponsible” (see go.nature.com/3bcyzfm). They included Michael Mina, an epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts, who says that the arguments are delaying a much-needed solution to the pandemic. “We continue to say we don’t have enough data yet, but we’re in the middle of a war — we really can’t get any worse than we are at the moment in terms of the case counts,” he says."

"Manufacturer data on test sensitivity come mostly from laboratory trials on people with symptoms, who tend to have high viral loads, Dinnes says. In those trials, many of the rapid tests seem very sensitive. (They are also extremely specific: they are unlikely to give a false positive result.) But real-world evaluations have flagged up apparent differential performance on people with lower viral loads."

"Deeks says that a December trial at the University of Birmingham is an example of how rapid tests can miss infections. More than 7,000 symptom-free students there took an Innova test; only 2 tested positive. But when the university researchers rechecked 10% of the negative samples using PCR, they found another 6 infected students. Scaling that up across all the samples, the test probably missed 60 infected students. Mina says that these students had lower levels of virus, so were unlikely to be infectious anyway. Deeks argues that although people with lower virus levels might be in the late phase of a waning infection, they might also be on the way to becoming more infectious. Another factor is that some students might have done a poor job taking swab samples, so that not many viral particles made it to the test. He’s worried that people will falsely think they’re safe with a single negative test — when in fact a rapid test is only a snapshot of likely non-infectiousness at that moment. Remarks that the tests could make workplaces completely safe are not the right way to inform the public about their efficacy, Deeks says. “If people get a false sense of security, they could actually spread the virus around,” he says."

"David Harris, a stem-cell researcher in charge of Arizona’s mass testing programme, says the different types of test have different uses: rapid antigen tests shouldn’t be used to assess the prevalence of a virus in a population, he notes. “If you use it like a PCR, you get a terrible sensitivity,” he says. “But in terms of what we’re trying to do — preventing the spread of infection — the antigen test, particularly when it’s applied multiple times, seems to work great.”"

"At the beginning of the pandemic, overstretched contact-tracers in the United States, Australia and the United Kingdom faced the extra burden of antiquated health-care systems. In Australia, as well as in US states such as Hawaii and Washington, health departments are often notified of new cases by fax or phone. “It’s somewhat embarrassing,” says Plescia, but “we never invested in the systems to allow them to do it differently”. Entering names and other details into a database from faxed notifications causes big delays, he says, so that the window during which contact-tracing might make a difference vanishes."

"Johnson's change of tack was to move finally towards lockdown, advising against mass gatherings and urging people to avoid clubs, pubs, and restaurants — and most travel — as well as advising older people to self isolate. (And of course, it was only 'advisory' – so that finance capital does not have to foot the bill for hundreds of thousands of insurance claims from small businesses.) But this has still left a gaping hole in government virus strategy. First, the World Health Organization (WHO) advice — "test, test, test" — is not being implemented. Health workers who were being organised to take on this role were almost immediately stood down. Everything is being done in secrecy: there is no openness, no transparency, no grown-up debate, no democratic scrutiny, no public accountability. We can only guess at the reason. Perhaps they realised it was hopeless because they didn’t have the testing kits. Perhaps it dawned on them that mass testing would reveal the vast numbers already infected and thus expose the scale of their negligence. What is certain is that willful blindness is central to Tory policy. There is virtually no testing anywhere. The WHO policy that you test, you trace, you isolate, you contain is being TOTALLY ignored by the Johnson/Cummings regime. They are not even testing health workers."

"This is putting thousands of health workers at risk, and essentially abandoning hundreds of them to catch the virus, to spread the virus, and in many cases to die. The experts in a health emergency are, of course, the health workers. But they are silenced by the Tories and the NHS bosses — threatened with dismissal if caught telling the truth to the public they serve — as if we were living in Stalinist China."