Mapping COVID-19: Inside the Epidemic Intelligence Unit

During a global pandemic, an infection can happen anywhere—a church, a car wash, a grocery store. But not every setting ends up spreading the virus far and wide.

That’s why Bridget Hanna spends her days looking at maps. For Hanna, an outbreak specialist with the Epidemic Intelligence Unit, these maps of Massachusetts towns don’t just give directions—they tell stories.

“Every COVID case is connected,” she says. “Which is to say, at a basic level, that everybody got it from someone else. But most people will get it from somebody who gave it to a couple of people. And that’s what really makes it a cluster.”

Partners In Health has staffed and supported the Community Tracing Collaborative (CTC) since April 2020, in partnership with the Commonwealth of Massachusetts and local health departments. Since then, the CTC has boosted contact tracing across the state, following up with positive cases and their contacts and connecting them with essential resources for quarantine.

But standard contact tracing isn’t the only tool in the CTC’s toolbox. Through the Epidemic Intelligence Unit, it’s looking to pinpoint the sources of multiple infections, or “clusters,” and use those insights to stop the spread.

Plotting a Pandemic

In public health circles, it’s called “cluster-busting.” The idea behind it is simple: most people will get the virus from someone who gave it to multiple people, or at a place or event where multiple people were infected.

So while standard contact tracing is important, it sometimes can be like playing catch-up. Cluster-busting, instead, looks at the bigger picture and offers a chance to get ahead of the virus—by finding out where a person became infected, who else was there, and what person, place or event was doing the spreading.

Cluster-busting has proven effective in Asian countries such as Japan and South Korea, where average daily cases sat at 1,556 and 421 respectively, compared to the United States’ 68,123, as of late February. In Massachusetts, where average daily cases sat at 1,707, public health leaders have been watching these countries closely—and taking notes.

The Epidemic Intelligence Unit (EIU) was launched in August 2020 as a specialized unit within the CTC, tasked with investigating COVID-19 clusters and delivering intelligence to health officials. The unit includes 40 case investigators and outbreak specialists.

Hanna is one of those specialists.

Her day often starts with reviewing tips from contact tracers—notes about people who tested positive and who reported being at a place or event with several others.

These settings can include workplaces, restaurants, birthday parties, funerals, and more. Since the vast majority of infections occur in a household, the Massachusetts Department of Public Health differentiates between clusters in the home, in long-term care facilities, and all other types. Generally, it defines a “cluster” as two or more confirmed cases with a common exposure.

“If a case investigator sees something like someone went to a wedding, we want to understand right away all the other contacts who were at that wedding,” she says. “Potentially, other people got infected there.”

She dives into the data, pulling reports from the CTC’s database of COVID-19 cases sent by local health departments. She wants to see whether other cases were recorded around the same place and time. That’s where the cluster maps come in.

“We can look at the report of every town and see that, ‘Okay, there are four employees of one auto garage who’ve been infected in the past three days…if we can figure out what’s happening quickly, maybe we can intervene to stop the spread,’” says Hanna.

She uses this data to plot the cases onto maps of Massachusetts communities, pinpointing the locations where the clusters occurred. That intelligence is then shared with local health departments, equipping them to take action.

Importantly, the data is always anonymized and all personal information is kept private. Outbreak specialists are ultimately looking for patterns.

“You get to learn so much about how the virus behaves in different environments,” says Ana Sanchez-Junkin, another outbreak specialist with the EIU. “I feel like we’ve learned a lot of things that help us with community outreach and educating groups in our community on how they can keep themselves safe.”

Working Smarter

Cluster-busting tackles COVID-19 not only retrospectively, but also prospectively. In other words, outbreak specialists don’t just look back in time, at clusters that occurred in the past—they also look ahead, anticipating where clusters may form and taking action to prevent them.

For example, if a person who tests positive is employed at a local business, Hanna can contact the business owner in hopes of preventing a cluster from forming, as contact tracers connect the employee with health care and essential resources. Or, if someone passes away from COVID-19 and a funeral is planned, Hanna and the team can proactively reach out to the funeral organizers and try to prevent the event from becoming a super-spreader.

Both kinds of cluster-busting provide crucial intelligence for health officials, equipping them with the data they need to shape their COVID-19 response.

Sometimes, the next steps are relatively straightforward. One of the first cases Hanna mapped was at a car wash in Chelsea. After detecting a cluster, she met with the local board of health to share her findings and they worked with the business owner to find a solution together—in this case, improving the car wash’s safety protocols, such as cleaning a touchscreen more often.

Other times, outbreak specialists look beyond a cluster of cases and broaden their focus to entire industries, such as retail or manufacturing, delivering intelligence that helps industry leaders and policymakers better understand how transmission occurs and take action.

Each case helps outbreak specialists deepen their understanding of the virus and how to stop it—offering a sense of hope amid a pandemic that has devastated communities and disrupted daily life for millions.

“What keeps us going are the success stories,” says Sanchez-Junkin. “For example, where you can help a business better understand how to stop an outbreak in the workplace…or, I had cases with some churches where they were able to go virtual for a few weeks and then help their communities understand how to keep themselves safe. I feel like those types of success stories are what makes the frustrations and the more technical aspects of the job worth it.”

For Hanna, the work feels both new and familiar. A longtime health advocate, she began her career as a human rights activist, spent years researching the epidemiology of the Bhopal gas disaster for her PhD, and taught global health with PIH Co-founders Dr. Paul Farmer and Dr. Jim Kim at Harvard University.

But this work takes her back to her undergraduate years, when she wrote her thesis on the industrial history of Massachusetts—a chapter she never expected to revisit, much less in the context of a pandemic.

“I know all this stuff about the old, industrial history of the state, which is useful to me as I’m making these calls to different industries and companies,” she says. “I’ve had a very unusual career path. But I feel like everything in my life has prepared me for this moment.”