The phased approach to relaxing New York City’s Covid-19 stay-at-home mitigation strategy requires effective containment to prevent a resurgence of infection. Central to containment is contact tracing. While the city has made significant progress in slowing the pace of new infections, the need for increased contact-tracing capacity remains an obstacle to a rapid, if phased, re-opening.

Ideally, we could test everyone and know for certain who is infected, but that’s an impractical goal. Contact tracing identifies people known to have encountered an infected person, then tests and treats them, thereby stopping further transmission. When infected contacts are found, they are asked to self-isolate for 14 days, because there is no known cure for Covid-19.

Contact tracing for infectious diseases has been a central public-health function for at least 150 years. When notified of a new case, trained contact tracers, working under the aegis of the public-health authority, arrange a confidential interview with the infected person. The contact tracer collects information about places the person has recently visited and people with whom he has been in contact with during the infectious period. In general, the effectiveness of contact tracing is measured by how many undiagnosed contacts are notified, tested, and treated, and by the degree of success in reducing the spread of infection in the jurisdiction.

Probably the most difficult challenge involves the completeness and usefulness of the data collected. People can have a hard time remembering where they have been and with whom they may have been in contact in the past week or so. And some individuals may choose not to disclose all their contacts or travels. Thus, the data on possible spread may be incomplete.

Nonetheless, a growing body of scientific literature supports the effectiveness of Covid-19 contact tracing and contact isolation to contain the spread of infection. Some countries, notably China and South Korea, have complemented the traditional model of contact tracing with sophisticated tracking software to identify potential contacts and isolate them. China, the nation with the most robust (and invasive) regimen of disease surveillance, requires almost everyone to install a tracking app on his mobile phone. Integrated with the user’s social and health profile, the app tracks his every movement, mapping his travels and recording his interactions. The user is notified if he is found to have come into close contact with an infected person. Notification may trigger a contact-tracing investigation; in some countries, notification may lead to severe restrictions on movement.

Apple and Google have announced a major collaboration to develop a version of the integrated surveillance systems that East Asian governments employ, with important concessions to American privacy standards. The Apple-Google software application will rely completely on self-management and will not share information with public-health departments. Integrating contact tracing with mobile phones seems like an obvious and efficient way to obtain real-time data about disease transmission, though this kind of surveillance can also lead to many needless tests and investigations and is not necessarily superior to traditional methods.

The use of software tracking intensifies ethical questions around privacy and liberty that always arise when tracing contacts in a disease setting. The goal of contact tracing, whether by people or software, is to protect the public, so arguments can be made for infringing on individual privacy and restricting traditional liberties. But important safeguards must be put in place, such as ensuring privacy training for contact tracers, securing and encrypting data, and refusing to share information with government agencies outside the health department.

Contact tracing remains an essential element of New York City’s public-health response to Covid-19, especially as the number of new cases continues to decline and the city looks to move from mitigation to containment—and to re-open its economy. While the city has begun hiring and training contact tracers, a political dispute over which municipal department would manage the process appears to have slowed down its efforts. The city estimates that it will have 1,000 tracers in the field by the end of the month and plans to add thousands more. Fortunately, the city is getting funding for hiring and training of staff from the Coronavirus Aid, Relief, and Economic Security (CARES) Act of 2020 and from private philanthropy (e.g., the Bloomberg Foundation in New York City). Current numbers of contact tracers are less than the projected need, but the city looks to be on course to build out a sufficient workforce eventually.

To avoid the risk of a second wave of infection, New York must expand its contact-tracing efforts while deploying enhanced technologies and addressing ethical concerns. Finally, to maximize the effectiveness of contact tracing, the city should continue to use it in tandem with other pillars of mitigation: increased identification of asymptomatic individuals through expanded testing and continued social distancing to reduce asymptomatic spread.

Photo by Justin Heiman/Getty Images


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