As COVID-19 continues to rage around the world, it is increasingly evident that contact tracing is central to managing the pandemic’s human consequences. A recent UK study found that adding effective manual contact tracing to a strategy of self-isolation and household quarantine of those testing positive for COVID-19 could reduce transmission of the virus by 64 percent relative to no intervention. Self-isolation and household quarantine alone would reduce transmission by around 37 percent.
Contact tracing is the process of identifying, assessing, and managing people exposed to a disease to prevent further transmission. When systematically applied, it can break a virus’ chains of transmission and is thus an essential tool in the public health arsenal.
It consists of three parts: contact identification, when everyone who has been in contact with an infected person is identified; contact listing, where all people considered to have been in sufficient contact with the infected individual are contacted to inform them of their contact status and share information about next steps; and, lastly, regular contact follow-ups to monitor for symptoms and test for signs of infection in this group of people.
Contact tracing has thus far been an inherently human-to-human function. In most cases, a significant level of clinical judgement and communication skill is required of those charged with contact identification and contact listing (presuming that close contacts can be located and are willing to engage in the first place).
Clearly, as COVID-19 numbers have exploded in parts of the US, contact tracing staff have come under significant pressure. Increasingly, neither sufficient numbers of trained staff nor funding are available to scale up operations sufficiently. This has led some to claim that US contact tracing systems are broken and that the situation is contributing to the spread of the virus.
Could smartphone applications such as Apple and Google’s joint API, Singapore’s TraceTogether, Australia’s CovidSafe, or New Zealand’s NZ COVID Tracer offer improvements in contact tracing without an army of trained humans? If so, then the case for spending COVID-19 stimulus cash on such a tool would seem to offer a double bounty.
Leaving aside the usual questions of potential privacy violations and the effectiveness of the apps being tied to how many users adopt them, the key question to ask is: How exactly do these apps complement existing contact tracing processes? It seems the apps are unlikely to replace humans but could help categorize contacts by identifying those most likely to qualify for listing. Human attention could then be focused on the most “valuable” cases, making best use of the scarcest resource in the contact tracing arsenal.
To this end, Bluetooth-based contact tracing apps appear to be the most promising. These apps automatically collect information when activated phones come within the requisite distance of each other for sufficient time. When an individual tests positive, the phone record is uploaded to contact tracing authorities, who can notify all relevant phones with information and instructions. Contact tracers can then focus on only those activities requiring their special skills.
However, these apps will not pick up information that only a human interviewer can elicit — for example, locations where the infected person may have left deposits of live virus particles that could subsequently infect someone whose phone never comes within close contact. These omissions could explain why the UK study found that contact tracing apps alone were less effective than human contact tracing systems in reducing transmission.
There is a small chance that the phones will mistakenly identify contact within six feet of each other, but physical barriers prevent virus transmission (e.g., between walls in an office or apartment block). While this may lead to too many alerts being automatically sent and further stresses on testing systems, it does not compromise contact tester time.
By contrast, apps such as New Zealand’s NZ COVID Tracer, which is based on users scanning QR codes, provide a better record of where an infected individual has been but fail to identify individuals encountered. Hence, they do not lend themselves to automated messaging. They may augment a human contact identification process by prompting tracers to try to obtain additional information about who was around when an infected individual was present at a specific location, but this could result in an information overload.
Unless all locations have electronic systems recording who enters and exits and how long they are there, even more manual processing is required for each infection case identified. Plus, these apps do not track activities in locations without codes where people may mingle and virus transmission can occur (e.g., parks and beaches), so they too fail to be comprehensive.
Smartphone apps do not appear to be a silver bullet for COVID-19 contact tracing. Human tracers will remain the hub of these systems even if some apps may assist in streamlining their workload. Smart policies must focus on both app development and training more contact tracers as we continue to battle the pandemic.
This article first appeared in AEIdeas on August 17, 2020.