The 19th-century physician turned epidemiologist John Snow discovered that water, not air, was the cause of the 1854 London cholera outbreak simply by asking victims about where they got their water. We are more technologically advanced now, but we could still apply old-school epidemiological tools to the data that public health departments routinely collect and get better answers about where infections from the novel coronavirus happen.

My public health professor defined “epidemiology” simply: It’s the study of the causes of disease. Diseases like covid-19 have immediate causes, like the coronavirus that emerged late last year. But they also have an array of causes behind the causes. Understanding underlying causes, like where and how an infection spreads, is a key for stopping any disease.

Because the virus spreads easily and through people without symptoms, we can’t completely isolate the risk of getting covid-19 to just some places or activities. But the risks of getting and spreading the disease are not the same everywhere, at every time, for everyone. And as the epidemic evolves, we might expect increasingly localized outbreaks.

We’ve also heard about many high-profile outbreaks. They’ve occurred at nursing homes, meatpacking plants, choir practices and prisons. That tells us that particular places are riskier. So far, we’ve just been speculating about where. But answering these kinds of questions is what epidemiology can do well.

Nearly 6 in 10 Americans who are working outside their homes are concerned that they could be exposed to the virus at work and infect their families. (The Washington Post)

Uncertainty about risks will get in the way of America reopening. A recent Associated Press/University of Chicago poll tells us that over half of Americans fear getting a haircut, going shopping or visiting a friend. Better facts about the location of the bigger risks might help people feel more confident about lower-risk activities. This information also tells public health officials where to target prevention efforts.

States and counties collect detailed data on every covid-19 case, but so far, they haven’t been using that information to say where risks are higher. The Centers for Medicare and Medicaid Services is now reporting covid-19 cases and deaths from licensed nursing homes. Otherwise, neither states nor counties nor the Centers for Disease Control and Prevention have been telling us how much different living and working conditions contribute to the spread of the disease.

One study in Asia found that work-related transmission played an important role in the early phase of the outbreak, with health-care work, driving and retail sales being riskier jobs. The reason this study was possible is because researchers were able to easily extract the case data from six different Asian countries.

We have the same opportunities in the United States now. The case report forms completed by doctors contain a wealth of information, like the type of place a person lives, their work, whether they had contact with someone known to be infected or whether they traveled recently and where, if so. These case reports eventually get funneled up from counties to states and to the CDC.

The work of contact tracers provides additional clues. The tracer’s main job is to get an infected person’s contacts in quarantine. We can learn from the tracer’s work how many contacts are being reached and how quickly, giving us a sense of how many infectious people are circulating among us.

Tracers can also learn about how and where people made contact. Was it in a household, at a bar, a church, a school, a grocery store or a public swimming pool? Were people sharing a meal, working together or walking in a park?

This rich data is an opportunity to more precisely understand our risks and to more precisely target our resources. What’s needed is collecting this data well, organizing it and making it useful to people. Countries like Singapore are reporting the exact location of every cluster of covid-19 infections. Privacy advocates in the United States might object to this. But gleaning epidemiological insights doesn’t require revealing any private information.

One challenge is that today each county collects data on covid-19 in its own way. We need the information in the same language, in real time and publicly available. So far, very little risk factor information appears to be making its way to the CDC. Calls for better information on ethnicity began months ago. The CDC director recently announced requirements for counties to report more facts, but he gave them until August to deliver. We should expect every bit of useful information to be collected. August is too long to wait.

All things considered, organizing and sharing this data should be one of our easier challenges. It’s not like we need to invent a new kind of ventilator. This is the country of big data and technology titans.

Understanding why and where covid-19 spreads may not lead us to the cesspool where the disease breeds, as it did for John Snow, but it may provide enough guideposts to lead us to safety. Health departments have been collecting this data for months already. It’s time to bring it together and use it.

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