Every strategy for releasing Covid-19’s vise-grip on daily life starts with identifying cases and tracing their contacts — the laborious task of public health workers tracking down people who have crossed paths with a newly diagnosed patient, so they can be quarantined well before they show symptoms.
That typically takes three days per new case, an insurmountable hurdle in the U.S., with its low numbers of public health workers and tens of thousands of new cases every day. Existing digital tools, however, using cellphone location data and an app for self-reporting positive test results, could make the impossible possible, the authors of a new analysis argue.
“Traditional manual contact tracing procedures are not fast enough for [the new coronavirus],” researchers at the University of Oxford write in a paper in the journal Science this week. But digital technology “can make contact tracing and notification instantaneous.”
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The “technology to the rescue” idea has been gaining steam as the coronavirus pandemic has outpaced everything Europe and the U.S. have thrown at it, and not because of a deluded belief that digital tech can solve all the world’s woes. Instead, this fix is aimed at a very specific problem: identifying cases of Covid-19 and quickly tracing everyone who came into contact with them before they infect others. That has helped countries such as South Korea, Taiwan, and Singapore beat back the epidemic, though sometimes through measures that trample privacy.
“We have evidence that this works,” said computational epidemiologist Maia Majumder of Boston Children’s Hospital, referring to contact tracing and case isolation. “The public health consensus is clear that this is what we need to do.”
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The U.S. and Europe have hardly attempted contact tracing, however. It requires an army of public health workers or intrusive policies that many of their citizens oppose. But this week brought efforts to circumvent both obstacles.
One high-profile effort is led by Trevor Bedford, an infectious disease modeler and genomics expert at the Fred Hutchinson Cancer Research Center in Seattle. This week, he and his colleagues launched “NextTrace,” a project based on the fact that traditional contact tracing doesn’t scale: With more than 200,000 cases in the U.S., and each case requiring hours of detailed follow-up, doing this by analog methods won’t work.
“So much of this virus’s transmission, maybe 15% of total cases, is from people who don’t feel sick,” said mathematical biologist Lauren Ancel Meyers of the University of Texas at Austin, who is advising NextTrace. “And it’s spreading so quickly, with as few as four days from when one person shows symptoms to when people he infects does. It would therefore take a heroic effort and very fast quarantine and isolation to identify, by traditional methods, every person who’s infected, and every person they contact, and everyone they contact.”
NextTrace therefore plans to build a decentralized reporting system in which anyone with confirmed Covid-19 can choose to register, anonymously, on an online platform. The platform will use cellphone location and proximity data from cellphones, for people who have opted in, to find individuals who might have been exposed to this case and advise them to be tested. The system would build a contact history for each case.
Exposed individuals can be tested and, if infected, isolated. The earlier that happens the more transmission drops: People shed the highest level of virus soon after symptoms appear, scientists in Germany reported on Wednesday in the journal Nature.
Basically, person A’s positive coronavirus test result would trigger an instant notification, again via the app, to individuals who have been in close contact. The platform would recommend isolation for that individual and quarantine of their contacts. The NextTrace team doesn’t specify if the information would be shared with public health departments, or how soon it might be up and running.
Since this approach can “scale massively, it could significantly affect an epidemic even after there is widespread community transmission,” said Meyers. The information on the number of exposed contacts would also allow for better targeting of containment policies, with greater or less social distancing depending on the intensity of community spread. “I do think that massive testing and contact tracing may be the key to lightening the social distancing measures. But it will have to be very aggressive.”
The new research by the Oxford team, led by Christophe Fraser, shows how to achieve that: Speed can substitute for effectiveness. If manual contact tracing takes three days, then it is essentially impossible to drive a disease’s reproduction number — how many cases each patient causes — low enough to stop an epidemic. (The reproduction number, R, needs to be less than 1 for that to happen.) If it takes two days, then about 80% of cases would have to be found and isolated, and 80% of the contacts of their contacts quarantined.
But with the instantaneous tracing promised by digital technology, said Oxford’s Luca Ferretti, an expert in pathogen dynamics and the first author of the Science paper, only 60% of cases would have to be isolated and 60% of contacts traced — and possibly as few as 50% and 40%, respectively.
Even these relatively low rates, he and his colleagues calculated, “could bring R below 1 and therefore effectively control the epidemic.” And they can do so more quickly than today’s stay-at-home orders, business closures, and other social distancing steps alone, and prevent a Covid-19 resurgence after the current pandemic fades — without re-imposing economically crippling social-distancing policies.
People should have the right to participate or not, both the NextTrace and Oxford researchers say. If uptake is too low, however, the digitally enabled instantaneous tracing wouldn’t find enough contacts to stop an epidemic.
A similar platform could serve as an early-warning system for the next outbreak of Covid-19, which may well return later this year even if it fades in the summer. With fewer cases, the level of Covid-19 testing will likely be even lower than it is today. That risks putting the U.S. exactly where it was this winter: with Covid-19 already seeded in a few cities and being spread undetected until it was too late.
“We’d like to identify regions where testing might not be happening and bring it to the attention of health authorities,” said Olivier Elemento of Weill Cornell Medicine, who before the coronavirus epidemic used big data for precision medicine. “Traditional contact tracing is hard to do in the U.S., but we think we can use technology to identify hotspots even before there are confirmed cases and alert their contacts.”
Using a tool he and his colleagues built, people can anonymously report symptoms (dry cough, fatigue, fever, and others) and where they live. It doesn’t collect IP addresses or otherwise track users. “But if we identify new clusters we will let states, counties, and cities know about them,” Elemento said, “so they could increase testing in those areas, put stricter social distancing in place, and alert local hospitals to a potential surge in patients.” A group at Boston Children’s Hospital and Harvard is developing a similar tool, as is one at the University of Alabama at Birmingham.
“These physical distancing measures, these stay-at-home measures, have bought us a little bit of time,” Maria Van Kerkhove of the World Health Organization told reporters on Monday. “[It] has to be used appropriately so that we get systems in place to look for this virus aggressively through testing, through isolation, through finding contacts, through quarantining those contacts.”
Andrew Joseph contributed reporting.
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New digital tools could speed up Covid-19 contact tracing - STAT
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