Hoping to understand the coronavirus, everyone is parsing a mountain of data

The latest count of new coronavirus cases was jarring: Some 1,500 virus cases were identified three consecutive days last week in Illinois, and fears of a resurgence in the state even led the mayor of Chicago to shut down bars all over town Friday.

But at the same moment, there were other, hopeful data points that seemed to tell a different story entirely. Deaths from the virus statewide are one-tenth what they were at their peak in May. And the positivity rate of new coronavirus tests in Illinois is about half that of neighboring states.

“There are so many numbers flying around,” said Dr Allison Arwady, commissioner of the Chicago health department. “It’s hard for people to know what’s the most important thing to follow.”

This is a pandemic that has been told in harrowing stories from hospitals, factories, nursing homes and meatpacking plants. But as the crisis stretches on, it is also unfolding in an increasingly complex spread of numbers.

Six months since the first cases were detected in the United States, more people have been infected by far than in any other country, and the daily rundown of national numbers Friday was a reminder of a mounting emergency: more than 73,500 new cases, 1,100 deaths and 939,838 tests, as well as 59,670 people currently hospitalized for the virus.

Americans now have access to an expanding set of data to help them interpret the coronavirus pandemic. They are closely tracking the number of sick and dead. They can read daily case counts in their cities and states, the percentage of positive tests, the number of people hospitalized and the weekly change in cases. It is possible to look on the Illinois Department of Public Health website and learn how many hospital beds exist statewide, how many ventilators are available in Peoria and how many intensive-care unit beds are free in Champaign.

Sophisticated data-gathering operations by newspapers, research universities and volunteers have sprung up in response to the pandemic, monitoring and collecting coronavirus metrics around the clock. Elected officials who were not particularly well-versed in public health or infectious disease when 2020 began now sound a little like epidemiologists, spending their days steeped in data and making policy decisions based on the figures before them.

“Everybody’s tracking this virus in a way that they’ve never done with any other infectious disease,” said Dr Amesh A. Adalja, a physician and senior scholar at the Johns Hopkins Center for Health Security, who has treated coronavirus patients. “For some people, it’s helped them understand what is happening. For other people, it’s been misinterpreted and not very helpful.”

He offered an example of an “armchair epi” from his own social circle: Scanning his Facebook feed recently, Adalja read a high school classmate authoritatively sharing information on the coronavirus fatality rate — far lower than the flu, the classmate asserted.

Adalja instantly saw that the calculation was flawed. “For flu, he used the denominator of total number of flu infections,” he said. “For coronavirus, he used the denominator for the population of the US”

He resisted the urge to type a hasty correction — Covid-19 is believed to have a substantially higher fatality rate than that of the seasonal flu — and kept scrolling.

Epidemiologists generally advise that the most important and revealing coronavirus trends can be found in the daily case count, the positivity rate, hospitalization data and the number of confirmed and probable deaths from the virus. But they also cautioned that data can be misleading and difficult to interpret, perhaps best seen as one piece in a larger, complicated puzzle.

“I view everything with a lot of skepticism,” said Dr Natalie E. Dean, an infectious-disease expert at the University of Florida. “I try and triangulate across a lot of different things.”

For many Americans, the numbers are a way to make sense of the pandemic — which is spreading in the South, West and much of the Midwest but calming in the Northeast — and to gauge whether things are better or worse in their own cities.

They often begin with the case count. That is the daily tally of individuals whose coronavirus infections were confirmed by laboratory tests, a data point that is frequently quoted, misused and debated.

“If I’m sitting at home and saying, ‘How is my community doing?’ I’d want to look at daily case counts,” said Dr John Swartzberg, an infectious disease specialist and a clinical professor emeritus at the University of California, Berkeley’s School of Public Health.

Those numbers are jaw-dropping. In the US, the cumulative count of people infected with the coronavirus has surpassed 4 million. New daily records tied to the case count have been alarmingly frequent in recent weeks: At least 16 states have posted single-day case records this past week. On Friday, more than 73,000 new cases were identified across the country, the second highest day of the pandemic.

There are several ways to parse the case count number.

President Donald Trump and other officials have frequently questioned the legitimacy of coronavirus case counts, falsely suggesting that a rise in testing availability is solely responsible for the increase in confirmed infections. More testing can cause an uptick in new reports of infections, but data shows that the rise in cases far outpaces the growth in testing.

Experts suggested that the daily case count is better viewed as a rough measure of whether an outbreak is slowing, expanding or stabilizing. A decrease in new confirmed cases could also indicate that testing is not available widely enough or that there is a backlog of tests that have not yet been processed and delivered to the local health department.

Time period matters, too. Comparing case counts in July to case counts in April is misleading, because many people were sick but few people were tested early in the epidemic. But comparing case count to a more recent period, when testing was relatively constant, is a useful measure.

Another frequently cited number is the positivity rate: the percentage of coronavirus tests that have returned with a positive result.

“The positivity number is one of the first places I go to,” said Gov. Mike DeWine of Ohio, who wakes up each morning to a fresh PowerPoint presentation from his staff, which he reads on his iPad before 8 a.m. “That’s what I zero in on.”

A rising positivity rate can point to an uncontrolled outbreak; it can also indicate that not enough testing is occurring.

DeWine is an avid reader of the daily PowerPoint presentation, which he calls the Situation Update. It started small in the early days of the pandemic. It has grown to at least 31 slides of numbers, charts and graphs — every day.

He said he also focuses closely on the number of Ohioans who have been hospitalized for the coronavirus, a data point that is difficult to spin or misinterpret. Last week, the pandemic approached an alarming milestone: About as many people in the US are now hospitalized with the coronavirus as at any other time in the pandemic, including during an earlier surge in the New York region in the spring.

“Hospitalization is a hard number,” DeWine said. “There’s no fudge on it.”

Yet even that measure has caveats. Hospitalizations do not reflect how many people are sick at home and experiencing mild symptoms — particularly younger people — but who could still be infecting others.

Dr Tara C. Smith, a professor of epidemiology at Kent State University who studies infectious diseases, said that viewed individually, much of the available coronavirus data can only offer a glimpse of the state of the pandemic.

“I think people tend to cherry-pick what they want to see, to confirm their biases,” she said.

She has been hesitant to place much stock in statistics on deaths caused by coronavirus, for instance.

“I see a lot of use of the fatality statistics, which are incomplete,” Smith said. “You do have deaths from coronavirus, but we know those are undercounted. For me, at least, that is not a particularly useful metric. But those are the type of statistics that some people grab onto.”

Perhaps the most telling numbers are trend data — examining which direction a community or state seems to be heading, said Michael T. Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy.

“There’s no magic number for any of this,” Osterholm said. “This is more like a windshield where you’re looking at everything in front of you. It’s not one piece of data. It’s all of it coming together.”

In 1918, newspapers in cities across the US published daily tallies of the sick and the dead from the flu pandemic, said John M. Barry, author of “The Great Influenza,” and public health officials made policy decisions accordingly, based on the data.

Today’s elected officials have far more granular data to consider.

In Chicago, Arwady, the city health commissioner, has a call with Mayor Lori Lightfoot every morning, discussing the city’s total cases, deaths, the seven-day average for testing and detailed hospitalization numbers, among other metrics.

“Data to me is one of the best ways to make it real for people,” Arwady said. She often tries to steer Chicagoans to look at coronavirus numbers broken down by ZIP code, so that they understand the risk they face in their own neighborhoods. “Mostly, I want people to feel like Covid is in their lives.”