The active impact of the new coronavirus is very different in China, where tens of thousands of people are sick, than it is in the rest of the world, which only has a few dozen scattered cases. But data from both environments is helping scientists as they work to understand the virus and the illness it causes.

“With a large number of cases you get a better sense of how the virus behaves on average in a community,” says Caitlin Rivers, senior associate at the Johns Hopkins Center for Health Security. “In a place with fewer cases, you can spend more time investigating each case.”

In the past week, researchers have published reports on large groups of coronavirus patients in China. One described the way the illness affected 138 patients at Zhongnan Hospital of Wuhan University, finding that around a quarter had to be cared for in the intensive care unit and that some patients had atypical symptoms like diarrhea and nausea. The study, published in the Journal of the American Medical Association, found that hospitalized patients passed the virus to 40 health care workers. Another team analyzed 1,099 patients from over 500 hospitals in China. In that set, fever and cough were the most common symptoms, and around 15 percent developed severe pneumonia. The data, which was published as a preprint, hasn’t yet been peer-reviewed or published in a journal.

Those studies and others like them give researchers a bigger picture of the outbreak. “It tells us a lot about what happens when you have a lot of overwhelmed hospitals,” says Angela Rasmussen, a research scientist at the Center for Infection and Immunity at the Columbia University Mailman School of Public Health. That helps public health officials in countries like the US prepare for what they might see if the virus continues to spread outside China.

Like any data from inside an active epidemic, though, the information comes with some caveats: usually, only the most severe cases of an illness come to the attention of public health authorities and are hospitalized during an active crisis. So the cases that are included in these reports may be more extreme examples of illness.

Doctors in China are also focused on treating patients and stopping the spread of disease, and they’re not collecting exhaustive data on individual cases. In places with only a few cases, like the US, researchers have the time to do more specific clinical evaluations of each patient.

“When you look at big groups, sometimes you can miss some of the subtleties that you could investigate in one person,” Rasmussen says. “In a crisis situation, there’s often not that kind of data collected because the priority is taking care of people who are really sick.” Each person’s body responds to a virus differently, she says, and having details on individuals can help highlight the various ways a person could react to an infection.

Individual case studies have their own limitations — no scientist would say that they have conclusive evidence from only one data point — but granular detail on single cases helps them understand how infections unfold. A recent case report on a US patient in Washington state, for example, included a day-by-day description of his symptoms and temperature. It also included all of his lab results, like his white blood cell and potassium counts. Another report, published this week, also tracked a Nepalese patient’s temperature over time and included images of his lungs.

With only a few patients to treat, public health officials in countries without large outbreaks can also focus on tracking down everyone a sick patient came into contact with. “In theory, you’d be able to find all the new infections,” Rivers says. The Centers for Disease Control and Prevention (CDC) is keeping close track of the close contacts of all the US cases, for example, and recording any new symptoms and testing them for the virus if necessary. That helps it understand how the virus is passed from person to person and how many additional people sick patients go on to infect.

These anecdotal case reports and large group epidemiological studies are precious to researchers as they scramble to learn how dangerous the new coronavirus is, Rasmussen says. “All the different studies are important.”


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