How contact tracing works
The details vary by disease, but the goal remains the same: to stop the spread.
A positive case is identified
Depending on the disease, a person who tests positive may isolate, receive treatment, or both.
Close contacts are identified
Contact tracers interview the person who tested positive to find out where they’ve been and who they’ve come in contact with.
Contacts are interviewed
Contact tracers get in touch with the person’s close contacts to inform them that they may have been exposed and to check for symptoms, provide guidance, and offer referrals to social service agencies.
Contacts are monitored
Contact tracers follow up with each contact to monitor for symptoms. If a person remains without symptoms throughout the monitoring period, the case is closed. If the person tests positive, the process begins again at step 1.
Regardless of the disease in question, contact tracing is based on the same premise: quickly identifying and monitoring people who have been in contact with an infected person in order to diagnose and treat them if they develop the disease — and to prevent it from spreading further, whether through vaccination or isolation. (The word “quarantine” dates back to the Middle Ages, when sailors had to remain aboard docked ships for a 40-day period — in Latin, a quarentena — to prevent the spread of bubonic plague.) Contact tracing allows health workers to find people who have been in contact with a carrier, to determine whether they are also infected, to offer support and treatment, and to build a list of that person’s contacts in case the tracing chain needs to expand.
What varies from disease to disease is who is considered a contact. Investigators look at the characteristics of the disease and how it spreads to determine who is at greatest risk of infection. Ebola, for example, is contracted through exposure to bodily fluids, so contact tracers monitored people who had had direct physical contact with an infected person — who shared meals with them, cared for them, did their laundry, or prepared their body for burial. With COVID-19, a respiratory disease, U.S. health authorities have defined a close contact as someone who was within 6 feet of an infected person for at least 15 minutes.
Some diseases, such as influenza, spread so rapidly that it’s difficult to keep up, says William Schaffner, a professor of preventive medicine and infectious disease at Vanderbilt University Medical Center. “It’s one of the difficulties we’re having with COVID-19 today.”
Another challenge in tracing the coronavirus, one that it shares with polio, is that many infected people are asymptomatic. “That very characteristic of polio baffled public health people for ages,” Schaffner says. “Before it was discovered to be an intestinal virus, they couldn’t figure out how it was spread. Some cases didn’t have any contact with each other.”
In the United States, health departments generally maintain a small staff of contact tracers; those teams are being expanded to trace the spread of COVID-19. San Francisco, for example, had only 10 people regularly working on contact tracing. The city reassigned other public employees whose workloads had lightened because of the pandemic to act as contact tracers — staff in “the city attorney’s office, assessor’s office, and, my favorite, all the city librarians,” says George Rutherford, a professor of epidemiology at the University of California at San Francisco and principal investigator on California’s contact tracing training program. Rutherford and his team were asked to train 10,000 civil servants online throughout the state. During a 20-minute interview with Rotary, he received 60 emails about it. “You can get an idea of the volume I’m dealing with,” he remarked.
Who makes an ideal contact tracer?
In New Zealand, Denise Garcia, a member of the Rotary Club of Tawa, was one of 190 contact tracers employed by the country’s Ministry of Health in the early phase of the COVID-19 pandemic. As a health professional, she was sought out to do the work. “They wanted people who could interview people and give advice,” she says. And her regular job as a midwife was deemed essential — “you can’t weigh a baby online,” she says — so she did both.
Like Garcia, the ideal contact tracer has strong interpersonal skills. One of the biggest challenges of the job, which is part detective and part social worker, is gaining people’s confidence. “They have to convincingly communicate trust,” Schaffner says. “Confidentiality is very important.” It can be especially challenging because of the social stigma of some illnesses and the mistrust in government by some groups of people. “People are wary of government intrusion, particularly at a time of turbulence — which there always is when there is a disease outbreak,” he says. “You have to come with a smile and a helping hand. But you have to get in the door.”