Assess plans to conduct contact tracing at scale

Contain and Control COVID-19

Lorene Nelson and Kevin Schulman on assessing plans to conduct contact tracing at scale

The COVID-19 pandemic has spotlighted a centuries-old practice for preventing transmission of communicable diseases. Public health workers around the United States are well-trained in contact tracing — tracking down people who interacted with someone diagnosed with a contagious illness, and providing those contacts with evidence-based advice for staying healthy.

The system is totally dependent on testing and the return of test results

Now, physicians, government officials and others in the public and private sectors are working to expand contact-tracing strategies to assist in containing the novel coronavirus. But in order for these practices to be effective, testing must be widespread and results must be available in a timely manner, says Kevin Schulman, MD, professor of medicine: “The system is totally dependent on testing and the return of test results.” Lorene Nelson, PhD, associate professor of epidemiology and population health, notes that it’s been a challenge for public health departments to hire and train enough people for contact-tracing efforts on the scale needed for COVID-19. However, she says, technologic solutions in development may help.

Below, Nelson and Schulman describe current efforts, along with promising innovations on the horizon.

What did contact tracing systems look like at the beginning of the COVID-19 pandemic?

Nelson: Contact tracing has been in place as a tool since the early 20th century to contain diseases, such as tuberculosis, yellow fever and, most recently, Ebola. It’s highly effective in those applications, but until recently, it hadn’t been used widely in a pandemic flu-type situation. That’s where the challenge really comes in.

Here in California, there are 61 public health departments for the 58 counties, and each of those has its own cadre of epidemiologists, who carry out contact investigations in routine public health outbreaks such as tuberculosis. However, with COVID-19, it became very obvious that more people were needed because the existing health department personnel couldn’t handle the increased workload.

Schulman: There are certain diseases that health care providers are required to report to the county, and that’s how the county finds out that somebody has, for example, tuberculosis; then they would get to work with contact tracing.

If you go back to the beginning of the COVID-19 pandemic, we didn’t have any tests. So, the first issue was how do you identify someone who’s infected with COVID-19 when we don’t have any good tests? And even as testing came online, it was restricted; we were testing patients in the hospital, but we weren’t testing patients in the community, so the health department wasn’t finding out about all of the cases.

After the pandemic began, how did officials in California adjust contact-tracing resources to better meet the growing need?

Nelson: Ultimately, the decision on how to do contact tracing is a county-by-county decision, and the counties vary widely in how they do that. In California, Gov. Gavin Newsom said his goal was to have at least 15 contact tracers for every 100,000 people in a county, and he wanted to have those people in place before he would consider reopening a county.

But it’s been very hard for counties to ramp up to that level of coverage. Newsom is providing counties with state employees that have been trained for contact tracing. He’s also offering other resources, such as software that enables health departments to track large numbers of people, record data about those individuals and follow those contact leads to other potentially infected individuals. Additionally, the state gave an $8.7 million contract to UC San Francisco to set up a sort of contact tracer training academy; this has helped counties throughout California to rapidly scale up the training of contact tracers.

Santa Clara County, where Stanford is located, has had a very robust response; their goal was to hire and train 1,000 contact tracers, and they were able to do that by July 31. Their contact tracers are primarily volunteers, along with some county and state employees.

Santa Clara County has the goal to reach the contacts of each infected COVID-19 (“index”) case within 24 hours of when the county receives notification of the laboratory test result. Unfortunately, in some counties, the lag time for reaching the contacts of infected cases is much longer, and a large percentage of contacts may ultimately not be reached.

What are some of the obstacles for successful contact tracing during this pandemic?

Schulman: The system is totally dependent on testing and the return of test results. One issue is that there may be some people who don’t want to be tested. For example, a service worker may want to be able to tell their boss that they’re not COVID positive because they need the paycheck. We also have asymptomatic people who aren’t getting tested or even evaluated by the health care system, so their contacts won’t ever be traced.

For those who are tested, if the test results are delayed — you find out that a patient got a positive test last week — well, they may or may not remember who they were in contact with when they were the most contagious. It takes four to five days from exposure to the virus to experience symptoms, and that’s if you even experience symptoms. How well you’re going to recall who you saw or where you were really is going to depend a lot on how quickly we get test results back to you.

Also, there’s no obligation for the index case to talk to the health department. There’s also no obligation for a contact to pick up their phone when a tracer calls. I think people are doing an amazing job with what we have. But it’s a really uphill battle.

What technologies have the potential to improve COVID-19 contact tracing?

Nelson: There are some digital contact-tracing apps that might provide an additional advantage when combined with contact tracing.

One is location based. It uses the GPS feature of your phone to retrieve the location history of where you have been. Once you’re diagnosed, public health workers can look back and see where you’ve been in recent days.

The other one is a privacy-protected approach that uses the Bluetooth-enabled capabilities of a cellphone. When someone with the app comes within a certain distance of another individual with the app — say within 6 feet for a minimum of 10 minutes — then the two cellphones exchange pings. Other than that, there’s no other data exchange. There’s no identifying data. There’s not even any location data; it doesn’t say where you were when your phones came in contact with each other.

If an individual with this app gets diagnosed with COVID-19, that person then notifies the system. Then everybody who has been within that threshold level of contact with the person gets notified. They don’t know who that person is. They don’t know where they encountered that person. They just know that they met the minimum threshold of contact with someone who’s since been diagnosed with COVID-19.

These are programs that have been developed by three main groups in the world: one in Oxford; one at MIT/Harvard; and one here at Stanford, called COVID Watch. It was developed by a graduate student in civil engineering, and it’s the first to be used in the United States in any systematic way. It was adopted by the Arizona University System, so all of the employees and students have been asked to download this app. It remains to be seen how that works. But this technology will probably work best in a place where downloading it is strongly encouraged — you need coverage of 60% or more of the population that you’re monitoring for this kind of technology to be effective.

Together, this type of innovation along with rapid contact tracing and rapid testing has tremendous potential to help us curb the spread of COVID-19.

Lorene Nelson, PhD 
Associate Professor of Epidemiology and Population Health

Kevin Schulman, MD
Professor of Medicine