Tracking Infection
While state and local officials bear most of the responsibility for policies related to Covid-19 within their jurisdictions, new federal guidelines promulgated by President Trump establish an important national standard for how to organize society during a pandemic.“The President’s Coronavirus Guidelines for America,” released on March 16, stress the importance of working and engaging in schooling from home; avoiding social gatherings of more than ten people; and refraining from eating or drinking at bars, restaurants, and food courts for the ensuing 15 days. The guidance has now been extended through April.
The goal of these restrictions is to slow the transmission of the coronavirus while increasing availability and accessibility of testing. Certain areas—infection hotspots—are experiencing high numbers of cases per 100,000 people and an exponential growth in cases, threatening to inundate local health-care systems and overwhelm health-care personnel. It’s well documented that widespread testing is not occurring, limiting our epidemiological understanding of the infection. At this point, it is unclear which other areas in the country might soon emerge as hotspots (though New Orleans looks likely).
The most effective means of interrupting transmission, of course, is to develop and deploy a vaccine that, by providing high levels of immunity, prevents an uninfected person from acquiring the virus from an infected person. By blocking transmission, vaccines not only prevent infection and complications; they also prevent one person from infecting many others. Unfortunately, we are at least a year away from having a vaccine for Covid-19.
But public-health departments do have tools for battling infectious diseases for which there is no vaccine. Contact tracing, for example, is a focused strategy for breaking transmission chains and controlling the spread of disease. It involves identifying infected persons; taking steps to prevent an infected person from further spreading infection, whether through isolation or treatment, if an effective treatment option exists; identifying those with whom the infected person may have been in close contact while infectious; and, finally, locating and testing these close contacts. If a close contact is found to be infected, the disease-investigation process starts again. The Centers for Disease Control’s Ebola control strategy illustrates how contact tracing can work.
Adapting this process to Covid-19, it’s important to identify asymptomatic or mild cases as well as severe cases because these cases can transmit the virus, too. In addition, we need to apply the CDC’s definition of a “close contact” to Covid-19. Being within six feet of someone for a prolonged period; or caring for, visiting, or living with a Covid-19 infected person, qualifies as close contact. South Korea worked from this definition, and it has been credited with reducing the proliferation of cases there. South Korea’s success so far, Science reports, owes to “the most expansive and well-organized testing program in the world, combined with extensive efforts to isolate infected people and trace and quarantine their contacts.”
To work effectively, though, contact tracing depends on certain preconditions—especially no existing barriers to testing. As long as testing remains incomplete or uncertain, public-health officials cannot draw lines of transmission accurately. The disease burden—its penetrance into the community—also must be low enough that it is practical for public-health officials to investigate people identified as infected, whether symptomatic or not; and the disease must not be so widespread that the chains of transmission become blurred or the area’s hospital system already overwhelmed with cases.
Even after infection has peaked and hotspots cool down, there will likely continue to be sporadic new cases. Contact tracing is most effective as a means of containing flareups. Applying this strategy in low-prevalence communities can prevent exponential growth in new cases, save lives, and protect health-care systems and their frontline workers.
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