Digital contact tracing a valuable complement to manual efforts

Digital contact tracing (DCT) is an effective complement to its manual counterpart, leading to better detection of secondary contacts, particularly with strangers, and may help contain the coronavirus disease 2019 (COVID-19) pandemic, a recent study has found.

Researchers performed a population-based controlled experiment in La Gomera, Canary Islands, Spain, evaluating the national DCT app Radar Covid with respect to two aspects: technical viability and epidemiological impact. The locality of choice had a population of approximately 10,000 people.

After a few days of marketing and communication campaigns to get the residents of the island to download the app, several outbreaks were simulated, such that around 10 percent of the DCT adopters were infected. Key performance indicators included adoption, adherence, compliance, and detection rates.

Through indirect survey data, the researchers found an adoption rate of around 33 percent, basing only on the number of verifiable downloads by offline promoters. This figure could be higher, they said, “and in-depth interviews indeed suggest a much larger adoption estimate.” Adherence was likewise difficult to assess due to privacy concerns, though indirect evidence also suggests high rates.

In terms of compliance, which refers to the percentage of infected individuals that would declare their status to the app, the researchers saw that of 349 simulated infections, 213 entered their status in the app; of an additional 43 secondary cases, 38 did the same. The overall compliance estimate was 64 percent.

Notably, after proper Bluetooth calibration, the DCT intervention was able to identify 6.3 close contacts per each index case simulated. Moreover, between 23 percent and 39 percent of these detected close contacts were determined to be strangers, according to survey forms.

“Overall results of the controlled experiment study are positive and we can conclude that, a priori, this technology works and after appropriate communication campaigns it might have the sufficient level of penetration and compliance to help and serve as a useful complement to manual contact tracing and other nonpharmaceutical intervention,” the researchers said.