Follow the science? It’s not that easy when deciding when — or if — to reopen schools

CPS and the CTU disagree on which metric should be used to determine if it’s safe to go back to schools, but experts say it’s far more complicated than what either side is advocating.

SHARE Follow the science? It’s not that easy when deciding when — or if — to reopen schools

The shifting metrics on when to reopen schools in Chicago has led to a debate on which data should be used to determine if it’s safe to go back.

Pat Nabong/Sun-Times

In March, a single case of the coronavirus in a Northwest Side school led Chicago Public Schools officials to close it.

By July, after the governor had shuttered all Illinois schools for the spring, CPS said its buildings would reopen in the fall as long as daily caseloads in the city were below 400 or test positivity was under 8% — a threshold that wasn’t met.

In November, as officials announced plans to reopen in the new year, they said the only metric stopping them would be if cases in the city started to double fewer than every 18 days.

City officials have attributed the changing thresholds to evolving science. They’ve explained that better recommendations are possible as more data becomes available, and that studies have shown that schools don’t appear to be superspreaders when strict mitigation is in place.

But the shifting thresholds and hard-to-follow metrics have confounded families and teachers and created a new and complicated twist in the debate over whether it’s safe to go back to school. The result is that a much lower bar has been set for a return to schools, a significant change that has been hard to stomach in a city where trust of public officials in many Black and Brown communities is already hard to muster, and where the virus is still raging.

The Chicago Teachers Union and many parents have gone so far as to question whether public health officials are moving the goalposts to allow Mayor Lori Lightfoot and CPS leaders to proceed with plans they’ve long wanted to implement.

‘You can’t really establish an absolute threshold’

So which metrics do scientists say schools should use?

It’s more complicated than any single number, several local and national infectious disease experts told the Chicago Sun-Times. Some argue the metric the city is using — doubling rate, which would allow schools to reopen right now — might offer an incomplete look at Chicago’s epidemic. Yet every one of them says the threshold the teachers union is pushing — 3% test positivity, which likely won’t be reached for months — is outdated and not particularly useful.

Dr. Daniel Johnson

Dr. Daniel Johnson

UChicago Medicine

“You can’t really establish an absolute threshold for saying that, ‘Oh, if you hit this number that means you have to close,’” said Dr. Daniel Johnson, chief of pediatric infectious diseases at the University of Chicago Medical Center. Closures could be necessary at a lower level of spread if mitigation protocols are ignored, while opening with a greater number of infections could be possible if strong rules are followed, Johnson said.

The data is most helpful, experts said, when considered with several other factors: How strictly mitigation protocols, such as mask wearing, are implemented and enforced; how strong of contact tracing and testing programs there are; and how well schools are set up to deal with occasional cases without having to shut down. All those are harder to accomplish in large, dense urban school districts like CPS.

The Chicago Department of Public Health has recently focused on doubling time as the most important metric, which is calculated by determining how many days it will take — based on the current rate of case growth — for the number of people infected since the start of Chicago’s second surge on Oct. 4 to double.

If cases are doubling in a short amount of time, that means the city is experiencing rapid spread, or an uncontrolled outbreak. The longer it takes to double, the slower the growth of the epidemic.

Dr. Marielle Fricchione (bottom right) of the Chicago Department of Public Health answers questions about the city’s school reopening plan at the virtual Board of Education meeting in December.

Dr. Marielle Fricchione (bottom right) of the Chicago Department of Public Health answers questions about the city’s school reopening plan at the virtual Board of Education meeting in December.

Chicago Public Schools/YouTube

Dr. Marielle Fricchione, medical director in CDPH’s COVID-19 bureau, said local data from the virus’ first wave showed the change from uncontrolled to controlled transmission happened around a rate of 18 days — the new bar that CDPH set for reopening CPS.

“There is no established metric at this time for when it is safe to reopen schools besides the presence of a controlled outbreak,” Fricchione told Chicago’s Board of Education at its monthly meeting earlier this month. “Changing metrics is not a reflection of chaos. Changing metrics is a reflection of good science.”

In November, Chicago’s doubling time was 12 days. Now, even as the region is still in the grip of the pandemic, the doubling time stands at 60 days. Yet Chicago as of Wednesday was still experiencing a rolling average of 1,171 newly diagnosed cases per day, about half the peak in November but still around the worst days in the spring.

That paradox, in which officials use one metric — doubling time — to justify sending students and teachers back to classrooms despite another — new cases — appearing to indicate widespread infections, has vexed parents and teachers.

And those frustrations could have merit, according to Dr. Justin Lessler, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

“If you have really high overall case rates, but you have a very low doubling time, you’re still going to see tons of cases in the schools if you reopen,” Lessler said. “Doubling time is important if your only concern is, ‘Are we potentially contributing, by opening schools, to a fast-growing epidemic?’ But you also have to look at how widespread the epidemic is when you’re opening schools because that’s going to tell you how many cases there are going to be [in the schools].”

Dr. Scott Braithwaite, who leads a team at New York University’s school of medicine that models COVID-19 outbreaks and has advised, among others, NYC Mayor Bill de Blasio on school closures, is a strong proponent of using doubling time — in conjunction with hospitalizations, case totals and other metrics — to make decisions about reopening any spaces where people gather, including schools. But in a city like Chicago, where the number of new cases identified every day is high, a long doubling time doesn’t on its own mean it’s safe to reopen, he said.

“I would be concerned about that burden,” Braithwaite said. “That doesn’t necessarily mean I wouldn’t open up the schools. Imagine it’s been that way for weeks and weeks and weeks, that same number, in other words it’s not accelerating. Then it may be possible to open up schools...

“But you wouldn’t just look at the doubling time and say, ‘Yeah, everything’s fine, open them up.’”


Students in New York City went back to school Dec. 7 after a three-week shutdown.

Michael Loccisano/Getty

Positivity rate ‘isn’t a very good metric’

The teachers union, which has unsuccessfully gone to court to keep schools closed for now, has been an especially vocal critic of the mayor and school system and, by extension, Chicago health officials.

Instead of doubling time, the union has demanded a 3% test positivity rate to be used — a mark that hasn’t been hit since March 5 — pointing to New York City’s public schools that closed in November once the city’s infections rose to that rate. De Blasio, however, has since decided to reopen schools even as the city moved above that bar and currently sits above 5%.

NYC officials first used the 3% positivity threshold because it was easily retrievable data, and they’ve since backtracked because “it isn’t a very good metric,” Braithwaite, the NYU doctor, said. He advised NYC officials to stop using positivity rate on its own because it depends on several factors that can vary unpredictably — such as who’s getting tested and how many tests are being administered — that make it difficult to identify useful information.

Asked if the CTU had spoken with a medical expert who could discuss the union’s stance on public health metrics for this story, spokeswoman Chris Geovanis said the union hadn’t brought in a paid medical consultant.

CTU attorney Thad Goodchild said the union is basing its demands on metrics used in other major cities, the threshold previously set by CDPH and the metrics used by state health officials to require out-of-state travelers to quarantine upon arrival to Illinois.

“What we’re proposing is not something we’re pulling from thin air,” Goodchild said. “Is the science evolving? Of course it is. We’re learning more about this every day. Is 3% the right number, or is it a different number? We want to bargain about that. CPS is refusing to bargain about that.”

“But one thing we’re clear about is we’re damn sure 12%, 13%, 20% in some zip codes, and [1,200] new cases per day, isn’t the number. And it’s outrageous for them to claim that it is and to trot out statistics that disregard the core metrics that the entire public health community has been relying on.”

Chicago’s positivity rate during the second wave this fall peaked at 16% last month and has since steadily fallen to just above 10%. Many neighborhoods, especially in Black and Latino communities, have suffered through much higher rates as, among other reasons, working-class parents and older students are forced to continue to go to work to support their families.

But Colleen Nash, a pediatric infectious disease doctor at Rush University Medical Center, said the metrics used in one city or state don’t necessarily translate to another, and one positivity rate in NYC “can mean something very different” in Chicago.

“These are two very different cities with large differences in population density, geographic distribution of that population and its health care resources and physical layout,” Nash said.


Chicago Public Schools CEO Dr. Janice Jackson speaks while Mayor Lori Lightfoot listens during a press conference at King Academy of Social Justice in Englewood on the first day of the fall semester.

Pat Nabong/Sun-Times

‘Once again, education was put on the back burner’

At the end of the day, no one metric is going to tell any community when to reopen its schools — only a comprehensive look at the epidemic, strong mitigation efforts and a prioritization of education will allow that, experts said.

In other places where officials have been more resistant to COVID-19 restrictions, schools have been open at much higher rates of transmission. Some studies have shown in-person schooling in communities with widespread infections has contributed to their local epidemic.

In Iowa, where the governor has been against strong pandemic protocols, schools have been ordered back in-person unless their county’s positivity rate averages 15-20% over two weeks. Three other states — Arkansas, Texas and Florida — have ordered schools open, with decisions on closures to be made in consultation with state health officials.

Many European countries such as France, however, have closed most other parts of society to slow the spread of the virus, including restaurants and bars, while keeping schools open. That strategy appears to have worked, slowing community spread even when transmission was high. In Chicago and other American cities like San Francisco and Boston, bars and restaurants have been first to reopen.

“When we made the decision to open up bars and restaurants and gyms and all those other things, and schools were an afterthought, that was incredibly discouraging as a lifelong educator,” schools chief Janice Jackson said on a webinar last week, “because once again, education was put on the back burner.”

Contributing: Brett Chase

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