Technical Difficulties of Contact Tracing

Abstract

In mid-October, thousands of English and Welsh citizens received phantom alerts that they had potentially been exposed to COVID-19. A quick Twitter tour reveals the spiraling fear, frustration, and confusion that ensued. Even though National Health Service (NHS) later updated the app, built using an Exposure Notification System (ENS) developed by Apple and Google, the incident still amplified mass hysteria and confusion.

The NHS bug demonstrates the real problem of false positives in digital contact tracing. A false positive occurs if the app alerts someone of possible exposure to coronavirus when no such exposure has occurred. A high rate of false positives has two potential problems. First, it could overburden a state’s limited testing capacity, as concerned citizens flood the already overwhelmed testing sites. On the other hand, people could become numb to notifications if the app continues to ping them with possible exposure. Then, people who really have been exposed will ignore the warning and not get tested.

While not as panic-inducing, false negatives can be just as deadly. A false negative occurs when a person who was actually exposed to the coronavirus does not receive a notification. If asymptomatic and unaware of a possible infection, she will continue her daily business and further spread the virus. Medical experts have dubbed such oblivious asymptomatic transmission “the Achilles’ heel” of the pandemic, especially as social distancing restrictions are relaxed.

Therefore, a digital contact tool must sufficiently minimize false positives and false negatives to ensure it does more good than harm. This is especially true as the number of U.S. states deploying digital contact tracing apps grows. In July, Google announced that 20 states and territories were “exploring” apps based on the Apple | Google ENS, which would represent approximately 45 percent of the U.S. population. New York and New Jersey’s recent app rollouts bring the total of state public health authorities currently using the Apple | Google ENS to eleven. In order to understand if the Apple | Google ENS is up for the challenge, we must understand the accuracy of the underlying Bluetooth technology. Long story short, Bluetooth technology simply cannot provide location information that is granular or consistent enough for digital contact tracing apps to reliably function.