Contact tracing has traditionally meant methodical, shoe-leather detective work. Tracers and epidemiologists interview people with infectious diseases to find out who they had contact with in the recent past and get those people to quarantine and to report who they in turn had contact with. Eventually tracers can track who actually brought a virus into a community and who might also be infected.
But today, the hope is that the shoe-leather work could be supplemented and made more accurate by the use of mobile phone apps.
A few states already have deployed GPS location technology to assist in such tracking while an alternate technology using Bluetooth signals is still in development.
In a series of TV interviews, mayors from New York City to Los Angeles, including both Democrats and Republicans, said they would ramp up contact tracing efforts to isolate infected individuals and allow the uninfected to go back to work.
States may use either the GPS-based approach or the Bluetooth route, or a combination of both, to track infected patients and people with whom they have been in contact. Although privacy advocates have raised fears about using GPS location tracking for contact tracing, some technologists and public health experts say that knowing the places that infected patients may have visited could be very useful to curb the spread.
Around the country, efforts are underway to use mobile phones to assist in contact tracing without hurting privacy.
Apple and Google are collaborating to develop a Bluetooth-based system that will serve as a template for programmers to build new tracing apps that would work on iPhones and Android devices. Researchers at the Massachusetts Institute of Technology’s Lincoln Laboratory also are developing and testing Bluetooth signals to assess the effectiveness of the approach. North and South Dakota have started using a GPS-based app called Care 19. Utah is using an app called Healthy Together that uses both Bluetooth and GPS location data.
Technologists and public health experts agree that no matter which approach is used it must guarantee users’ privacy, which is key to large-scale voluntary adoption of smartphone tracing apps. The American Civil Liberties Union in April backed the Bluetooth approach by Apple and Google, calling it a “strong start.”
Typically, when someone tests positive for the virus, their details, including a phone number, go into a public health database — many states use cloud-based software called Maven to track the spread of the disease — and that information is then shared with the Centers for Disease Control and Prevention.
State public health officials then call the infected person to map their movement during the previous two weeks to try and identify all the individuals the patient may have been in contact with. They then alert those people about possible exposure and try to isolate anyone with symptoms.
Tim Brookins, a Microsoft engineer, has developed the GPS location-based app that’s already in use in North and South Dakota. Brookins, who built the app on his own without his employer’s involvement, earlier had worked with North Dakota Gov. Doug Burgum when the latter was a technology entrepreneur.
For contact tracing to be effective, infected individuals must be able to recall all the places they may have visited in the two weeks before testing positive for COVID-19, Brookins said.
The Care 19 app serves as an electronic “diary of places you have been” and can help people recall their movements, Brookins said. When a user downloads the app, it assigns a random number to the device, which is then used to track the movement of the individual, Brookins said.
The app is compliant with the California Consumer Privacy Act, or CCPA, and collects location information only with the user’s consent, Brookins said. The data is then stored on a secure database managed by Brookins. The GPS coordinates of places visited by the user are then compared with a database of commercial establishments maintained by Foursquare, he said.
If a user consents, then the location data collected by the app would be electronically shared with state public health officials to help with identifying people who may have been exposed, Brookins said.
Not just whom but whereKnowing the location of infection transmission is as important in some cases as the person infected, said Louise Ivers, the senior medical adviser to the MIT program called Private Automated Contact Tracing.
“We know transmission happens through droplets and also through environmental contamination, and in some cases the actual location is involved in the transmission, such as a meatpacking plant, or a Walmart location,” said Ivers, who is the executive director of the Massachusetts General Hospital Center for Global Health and an associate professor of medicine at Harvard Medical School. “The actual location of transmission is an important part of the vector.”
Unlike the Care 19 app being used in the Dakotas, the MIT program is based on an approach developed by Ron Rivest, a world-renowned expert on cryptography, using Bluetooth signals and has become the “inspiration for the effort by Apple and Google,” said Israel Soibelman, chief strategy officer of MIT’s Lincoln Laboratory.
Anyone who voluntarily downloads a contact tracing app using the Bluetooth approach would enable their phone to send out a Bluetooth signal in the form of a random number every few minutes that is then recorded both by the user’s phone and by nearby phones that have similar apps. A record of what has been transmitted and received is stored on phones for a few weeks.
When a person using the app tests positive for COVID-19, the user can then voluntarily upload a log of their Bluetooth signals to a so-called exposure database, where only the random numbers are stored with no other identifying information. Uninfected individuals can check the database to see if any of the random numbers stored on their devices match any of the numbers identified as those of an infected person. If they match, then the healthy person can decide to get tested or isolate themselves to stop the spread.
Researchers are still grappling with fine-tuning Bluetooth signals to assess how accurately they measure the distance between two devices as well as the time two phones were near each other, said Marc Zissman, one of the principal investigators on the MIT project.
MIT researchers are working with data from more than a dozen national labs as well as smartphone makers to understand how far Bluetooth signals can travel from one device to another and how well the distance between two devices can be measured with those signals, Zissman said.
The lab is using robots to move phones around and measure signal strength, Zissman said, because the Bluetooth waveform was designed to communicate, not to measure distance.
Apple and Google have specified standards that apps must adhere to in order to be allowed on the App Store for iPhones and for Google Play store for Android devices. These rules stipulate that apps must be created by or on behalf of public health authorities, require users’ consent to send and receive signals, and must not allow any advertising through the apps.
Although mobile phone technologies may assist in the contact tracing effort, states will still need to hire thousands of public health workers to call and track infected patients the old-fashioned way. The Association of State and Territorial Health Officials has estimated that the United States would need 300,000 contact investigators, or roughly about one caseworker per 1,000 people.
Congressional Democrats, led by Delaware Sen. Chris Coons, proposed legislation last week that would expand national service programs by creating 750,000 positions, including the 300,000 public health jobs identified by state officials as needed for contact tracing.
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