The goal of all contact tracing is to slow (and eventually, halt) the spread of a pathogen. It accomplishes this by identifying and informing anyone exposed to that pathogen, so the exposed individual can get tested, self-isolate, and avoid infecting others.
The way contact tracing is done depends upon the pathogen being traced.
In many cases, health workers or dedicated contact tracers interview infected individuals—often by phone—to understand possible points of exposure. This might be followed by public notification (for instance, if someone infected with measles flew on a plane) or private notification (if someone infected with a sexually transmitted disease had unprotected sex).
Contact tracing is especially critical for pathogens like SARS-CoV-2, which can spread even if infected people are asymptomatic. Leveraging experience with HIV, tuberculosis, and other infectious diseases, countries and communities around the world have mobilized unprecedented numbers of contact tracers—tens of thousands of them—to track the person-to-person spread of coronavirus and notify individuals who may have been exposed.
But even these historic efforts are being outpaced by the rapid speed of transmission. In the United States alone, an estimated 100,000 contact tracers would be required to meet health system needs.
Digital technologies—from smartphones to open-source software—could help bridge the gaps.
Contact tracing goes digital
As ministries of health and health departments adapt existing contact tracing systems to meet the needs of the COVID-19 pandemic, many are looking toward digital tools to support their efforts. Existing tools like text message systems and health information systems have long enabled contact tracing for infectious diseases, but addressing an outbreak of this magnitude requires robust tools designed for health emergencies.
Epidemiologists and contact tracers use these systems to record the information they collect during patient interviews, notifications, and outreach. Contact tracers also receive reminders about additional follow-up or outreach that is needed. Data from these systems are then available for health managers and epidemiologists to understand and visualize the spread of COVID-19.
This approach to digital contact tracing can streamline data collection, improve the quality and availability of data, and provide insights that support rapid decision-making. But digital technologies also create opportunities to do something completely new.
Turning everyone into a contact tracer
In May 2020, Google and Apple launched the Exposure Notification System—software that turns Apple and Android phones into contact tracing devices. Using Bluetooth technology, this software allows phones to “talk” to each other and record nearby devices. When a person reports a positive COVID-19 test, any device that has had close contact will be notified of potential exposure. And this approach is being used by other companies and software around the world.
This decentralized approach uses technology, rather than a human contact tracer, to directly notify individuals of their potential exposure. Individuals can more quickly decide whether to isolate or take other preventive steps. Data from these apps can also be used by public health authorities to augment their traditional contact tracing programs.
Limits to the system
Decentralized, digital contact tracing has immense potential—but this potential is tempered by the potential risk and requirements. As this technology becomes more widespread, we must consider how its use may reinforce the digital divide.
- Health data are some of the most personal and sensitive information—and protecting this data is foundational to successful digital health. Combining health data, demographic data, and location data in a single platform increases the potential risk. Because of that, privacy, security, and trust must be at the center of these tools.
- To reach peak effectiveness, at least 60 percent of the population must be actively using these applications. But more than 4 billion people still lack access to mobile internet services—so building a contact tracing system based on Apple, Android, and other “smart” devices will leave whole communities behind.
- Many of these decentralized apps rely on individual reporting. Rather than triggering follow-up conducted by a trained and paid third party, individuals must be willing (and remember) to report positive COVID-19 tests within the app. Users of these apps must also trust that other users will report their positive tests.
- These apps do not replace the need for resources and information. When someone receives a notification of potential exposure, they also need to understand what this exposure means for their risk of contracting COVID-19 and what they should do next.
It will be very important to get this technology right. Digital contact tracing will be a vital tool for future disease outbreaks—and getting it right now means less time wasted during the next health emergency. And while we want to use every tool available, we should apply these technologies in a way that overcomes inequity—instead of adding to it.