Get the Facts About COVID-19 Contact Tracing: Q&A with Dr. Jonathan Zenilman

Jonathan Zenilman, Professor of medicine and chief of the Division of Infectious Diseases at Johns Hopkins Medicine


As public health officials in the United States and throughout the world work to contain the spread of the novel coronavirus, contact tracing – in which public health workers trace the chain of disease transmission from a patient with COVID-19 (the “index case”) and identify their contacts – is a crucial part of efforts to limit the virus’s reach.

Contact tracing is a common tactic in the field of public health and has been previously used for disease outbreaks including tuberculosis, sexually transmitted infections, measles, and HIV. However, contact tracers in several areas of the country have been stymied by low response rates and mistrust from the community.

To understand the importance of contact tracing in combating the ongoing spread of COVID-19 and what people can expect if they receive a call from a contact tracer, the Hub reached out to Jonathan Zenilman, professor of medicine at Johns Hopkins Medicine to learn more.

Why would someone receive a call from a contact tracer?

You would receive a call if you were identified as having been in close contact with somebody who has COVID-19. The idea is that when you have an infectious disease, there is something called the “infectious period,” which is the length of time someone is contagious. For most diseases, this is a limited period of time that’s well known. When someone has the infectious disease that you’re tracing, you go back to the time when they first became infected, and then estimate the moment they became infectious and were able to transmit the disease to others.

For COVID-19, people become symptomatic on average after five days, but the infectious period begins two days before that and can continue for a week to ten days afterwards. The goal of a contact tracer is to identify all the individuals that they had close contact with during that period – for COVID-19, it’s currently defined as anyone within 6 feet or having household contact. For other diseases, like tuberculosis, which is similar to COVID-19 in many respects, the infectious period is months long, so the period can vary quite a lot.

What happens when an individual receives a call from a contact tracer?

If I had COVID-19, for example, a contact tracer would ask me to identify everyone I’ve been physically close to in the past week. They might contact my wife, my neighbors, or anyone else I’ve been in physical proximity to. The contact tracer would then reach out to those people and introduce themselves and their affiliation, which is usually a local health department. They’ll verify your identity and information, and then they’ll inform you that you’ve been identified as having been in contact with someone who has COVID-19.

After identifying these contacts, the contract tracer reaches out to the next round of contacts and the process essentially repeats itself. The steps for individuals to take, then, varies depending on the disease, typically depending on whether there is available therapy. For an STD or TB, contact tracing means being tested and receiving treatment. For COVID-19, hearing from a contact tracer would result in testing and a quarantine period.

What type of information will a contact tracer request?

The information they’ll ask for – and each local situation will be different – will be if you have any symptoms related to COVID-19, if you’ve been tested for COVID-19, if you have underlying conditions that can make you more susceptible to the disease (like immunosuppression, hypertension, or diabetes) and they’ll often recommend or arrange for you to get tested. They’ll likely recommend that you quarantine in your house for a set period of time that adds up to fourteen days since the time of exposure.

What happens to the information a contact tracer collects?

While the information is not anonymous, it is confidential. This includes the source contact as well. If you ask the contact tracer, they will not be able to provide the name or any information about the source contact for reasons of confidentiality. Sometimes the source contact can be apparent, however, such as a spouse or a household member. All of this information is maintained within the health department, usually at the county or city level, but in some cases it could also be at the state level. This information is not given to anybody like an employer, insurer, or other individuals. If you are confirmed as a case of COVID-19 due to contact tracing, you will then be interviewed by the contact tracer and the cycle will continue.

Is information collected through contact tracing truly secure?

I think this is connected to a bigger anxiety and concern we are struggling with over the internet, data, and privacy. It’s important for people to understand that this is one of the few tools we currently have to actually fight COVID-19. Information provided to contact tracers is one of the most secure kinds of health information that there is. Consider that people have been doing contact tracing for STDs like HIV for many decades and that information has been securely held that entire time – it never appears in newspapers, on the news, or on the internet.

Any data that appears in public (such as case numbers) are never associated with personal identifiers. At its most specific, it might be reported at the zip code level by age, race, or gender, to aid epidemiologists in their work, but there are specific rules in place to protect the identity of the individuals. The health department will almost never release this information unless it’s under extraordinary, highly unlikely, and tightly regulated proceedings like a court order.