Contact tracing identifies people who have an infectious disease (cases) and people they came in contact with (contacts) who may have become infected.

This classic public health practice identifies and isolates cases and quarantines contacts until it can be determined they are not infected and cannot transmit the disease.

This has long been the province of government health departments, but the COVID-19 pandemic has shown that private enterprises have the incentives and ideas to perform contact tracing faster, more effectively and at lower cost, while protecting the privacy of both cases and contacts.

To reopen and restart our economy, employers must make it safe for workers to return to work. Their immediate goal is to limit absenteeism due to employee illness or fear of returning to work. But classic, government-run, contact tracing is ill-suited to accomplishing these goals for COVID-19.

Historically, contact tracing interviews infected persons to ascertain possible contacts and then employs armies of tracers to track down these contacts. A pandemic already as widespread as COVID-19 will require enormous numbers of contract tracers — 180,000 additional tracers could be needed.

Even if these tracers can be hired and trained, peoples’ memories are highly fallible — they may not remember who they were in contact with or have even be aware of some contacts. Like pandemic influenza, COVID-19 likely has a high rate of pre-symptomatic transmission.

Approximately half of COVID-19 patients are asymptomatic and can transmit the virus to others for an extended period, 14 days or more. In addition, a large number of infected people are pre-symptomatic — they have no symptoms at the time they test positive but go on to develop symptoms later.

Viral loads were similarly high in symptomatic, pre-symptomatic and asymptomatic persons, indicating that both pre-symptomatic and truly asymptomatic people play a role in transmitting the virus.

By the time asymptomatic, pre-symptomatic, or mildly symptomatic cases are identified and isolated, if they are identified at all, the virus will have been widely transmitted. Contact tracing will be delayed and ineffective.

There are too many infected people to think that widespread testing and in-person contact tracing can identify and find every cases’ contacts.

Luckily, private sector initiative and innovation are coming to the rescue. Multiple large companies are exploring novel means to ensure workplace safety and to make contact tracing more efficient.

Amazon has functioned as a safe source of critical supplies to Americans sheltering in place. Their large indoor warehouses employ thousands of workers.

Amazon has supplemented screening employees and mask requirements by repurposing security cameras to identify close contacts of people who test positive to facilitate contact tracing. Amazon is also testing wearable devices that alert employees in real time when they come too close to another.

These techniques can be scaled down for smaller employers to ensure greater workplace safety at minimal marginal cost. It is likely most workers will consent to these measures since they prefer working in a safe, if more intrusive, workplace.

Another approach relies on smartphones — 81 percent of Americans own one and ownership is especially high in working-age populations (92 percent or more in ages 18-49 and 79 percent in ages 50-64).

Smartphones already have technology for large-scale contact tracing through location data, which fuels many applications such as traffic information in navigation apps. Korea relied on this capability to publish the routes cases had taken and to notify contacts who were in the locations.

However, aggregating precise location data for specific individuals smacks of surveillance and creates the potential to expose the case’s identity.

To allay these privacy concerns, Apple and Google, whose operating systems control nearly all U.S. smartphones, worked together to create an “exposure notification” tool, using Bluetooth technology already in the phones.

Bluetooth excludes location data, which is why you can listen to your wireless headphones while in “airplane” mode. The Apple/Google system allows nearby phones that have opted into the system to passively exchange and store randomized, anonymous identifiers with one another.

If a person tests positive for COVID-19 they can report it anonymously to the system.

An alert is then sent out to all the phones opted-in to the system that came in close contact with the case’s phone over a given period, encouraging the recipients to get tested while preserving the anonymity of the positive case. There is no way for the contacts to connect up a particular location to where they might have seen the case.

Government could use the location data features of smartphones for contact tracing as has been done abroad or use the new Apple/Google exposure notification tool.

But digital contact tracing cannot work without the cooperation of the population; otherwise, people will opt out by shutting down the location and Bluetooth features on their phones. Suspicion of government use of these tools may further limit their acceptance.

Voluntary uptake can be enhanced by businesses with an incentive to create safe workplaces offering digital contact tracing to employees who want to be assured of safety and privacy.

Employees and employers can collaboratively experiment with the Apple/Google system to create the best contact tracing apps for their particular circumstances, leading to greater buy-in and efficacy.

People 20 and older in the labor force account for about two-thirds of the population 20 and older.

If a high percentage of employees opt into the Apple/Google system, we will have an efficient, low-cost, contact tracing platform covering a high percentage of the population instead of the labor-intensive programs governments currently employ.

Relying on old-fashioned contact tracing will not get Americans back to work.

But American innovation will.