At the start of June, public health officials wondered whether major street protests over police killings of African Americans would lead to a spike in coronavirus cases.
Crowds of people, at times shoulder to shoulder, had marched through Chicago and some suburbs at a time when people had been told for weeks to stay away from each other as much as possible.
Dr. Ngozi Ezike, the state’s health director, called it a “cause for concern,” while the city’s top health official recommended demonstrators avoid people older than 60 or with underlying health conditions.
So far, the available data shows no significant spikes in COVID-19 cases, however. Chicago was averaging about 400 confirmed cases a day when the protests began, and that number has since dropped to under 200 a day as of Friday.
“It’s too early to say definitively whether we’re seeing an increase or change. But, to date, we have not,” said Dr. Jennifer Layden, chief medical officer at the Chicago Department of Public Health.
Experts say it’s possible the virus didn’t spread as much because of the outdoor nature of the protests and the fact that many demonstrators wore masks.
Still, public health officials and researchers caution it can be difficult to know the effect of protests for certain, given all the variables.
Why so hard to pinpoint?
The protests started May 29, a Friday night, when roughly 200 people marched through the Loop and Near North Side. Over the next week, the demonstrations grew to include thousands across the city and suburbs.
It takes roughly five days for an infected person to show symptoms, meaning that infections occurring at those times likely would have emerged by now.
But a lot of other things have been going on, too, researchers said. People have also been going out more, whether to eat, travel, or just hang out with friends and family. It’s not like demonstrations occurred in a petri dish, where scientists can study what happened in a controlled way.
And those interactions also contribute to spread and could “drown out any signal coming from protests,” said Nigel Goldenfeld, a University of Illinois physics professor who is working with colleague Sergei Maslov to study the virus’s spread.
“It would not be justified to attribute to peaceful protests any upticks in prevalence without first ruling out other equally plausible origins,” Goldenfeld said.
The data, at least what’s collected so far, isn’t precise enough to figure out infection sources. And health officials are weeks or months away from ramping up the kind of robust contact tracing that could better identify so-called superspreader cases originating from large public gatherings, such as protests.
Jaline Gerardin, a Northwestern University assistant professor of preventive medicine who has worked on virus modeling, said trying to answer the question would require “really high-quality contract tracing” as part of extensive research.
“That would be a lot of legwork to really get the volume of data needed,” she said.
It means that, to monitor infection trends, you have to look elsewhere — such as figures for emergency room visits, confirmed cases and hospitalizations.
ER visits
One of the earliest potential indicators of the virus spreading is people showing up to the emergency room with symptoms that might be COVID-19.
Health officials have long monitored ER data, particularly for signs of the severity of seasonal flu. It’s evolved in this pandemic to also include cases of people complaining of COVID-like symptoms.
“When we think of someone who’s COVID-infected, they’re not going to get a test unless they go see a provider, and one of the places they go to get tested is in the emergency room,” said Layden, the city’s chief medical officer.
The ER data system can tag cases before test results come back, which offers an early warning. The data for Chicago is promising.
City charts show that about 10% of ER visits involved COVID-like symptoms in late May. By June 16, they were averaging near 2.5%. ER visits for flu-like symptoms were nearly 13% of all ER visits, on average, in late May, dropping to less than 5% by June 16.
Case data
There are other metrics that experts already have been watching to spot a second wave. One of them is case data — the number of positive test results each day. That includes people who went to the ER and got tested, as well as those tested elsewhere.
The good news is that unlike in other states the numbers in Illinois continue to trend down.
Health officials report a similar trend for Chicago, the heart of the demonstrations and unrest. Looking at a seven-day average, daily case tallies averaged more than 400 the day the protests began, and have since dropped to under 200 through Friday.
(In the chart below, you’ll notice the city’s figures show regular spikes in daily case counts. The spikes appear to occur on weekdays, when more tests typically are performed.)
(If the city figures look different to you, that’s because the state has a different way of counting confirmed virus cases. The city counts a positive test on the day the test was taken. The state counts a new case on the day test results come back, which can sometimes be several days after a test was taken. But even looking at it that way, the trends still hold, with average case counts dropping in half from the first day of the protests through Friday.)
Still, there are caveats with this data. After all, it’s not based on random samples of people, which experts say would be far more illustrative of the pandemic’s reach.
Rather, these figures could just be showing more people choosing to get tested, as more tests become available, with no clear link to the pandemic’s broader rise or fall.
Sarah Cobey, a University of Chicago associate professor who has done virus forecasting, said protesters may be heeding health officials’ request to seek testing, leading to them being over-sampled. That would make it harder to draw broad conclusions about how much the virus is spreading.
But there’s another figure that could shed better light.
Hospitalizations
One way to avoid some of the problems with using positive case data is to narrow it just to counting COVID-19 cases when people are admitted to hospitals.
After all, people sick enough to be hospitalized, in general, have been tested throughout the pandemic. And while the testing protocols across hospitals and time haven’t been perfectly equal, researchers say they offer far more consistent ways to measure pandemic trends.
In Chicago, amid the protests, the city’s hospitals were collectively admitting about 30 to 40 people a day with the disease or COVID-like symptoms. In the most recent week, it dropped to less than 20 each day.
There is a statistical catch, though. For that unfortunate subset of infected people requiring hospitalization, it can take someone a week, even after showing symptoms, for them to worsen to the point of needing to be admitted to a hospital.
That could make it harder for researchers to see immediate effects in daily hospitalization figures, particularly from any secondary infections of people well enough to avoid hospitalization to family or friends who may not be as lucky.
Why no spike (so far)?
Health officials and researchers say that while they don’t know for sure what’s going on, they suspect the nature of the demonstrations may have played a part.
Experts believe the main way the virus spreads is from respiratory droplets spewed from infected people talking, coughing or sneezing. And poor air flow can allow those droplets to linger in the air.
Interactions during the protests often occurred outdoors, where there’s more air flow that dissipates droplets. And researchers said it appeared from pictures and videos of protests that attendees mostly wore masks, which are believed to significantly cut down on the spread of droplets spewed from infected people.
Still, some interactions involved tear gas and pepper spray, which can lead people to tear up and cough. And sometimes, crowds swelled close together, whether it was marching or when police attempted to corral or funnel protesters — not to mention those jailed in conditions that further the spread.
In essence, it’s a mixed bag, without definitive data to dig into. So researchers caution against assumptions that the protests, by themselves, could lead to a second COVID-19 wave.
“The risk of COVID-19 transmission associated to many protests against police brutality and racism may be perhaps small. Many small, short protests outdoors will probably not contribute as much in the way of super-spreading or transmission as a single huge protest,” said Goldenfeld, of the U. of I.
“Probably the bigger risk of transmission comes from the aftermath of tear gas or being held at close quarters during arrest by police not wearing masks,” he said.
