There's one number Chicagoans should be following most when it comes to coronavirus data being released by the city's health department, according to the city's top public health official.
It's the same number that largely guided public health officials as they halted indoor bar service in the city and switched public schools to remote learning for the start of the school year: the daily case average.
As of Wednesday, the city saw a rolling average of 277 cases per day. And the number is on the rise.
One month earlier, that number, which Chicago Department of Public Health Commissioner Dr. Allison Arwady said "is the best reflection of the burden of our disease," was consistently below 200.
"The fact that over the last four to five weeks we've added between 80 and 100 cases and not seen signs of that turning around makes us concerned," Arwady said Wednesday.
During the peak of the pandemic, Chicago was averaging about 1,000 cases per day.
The current daily average puts Chicago in a "high incidence" state.
"If we've added 80 to 100 new cases over the last month, without seeing turnaround, we very easily could add that many or more in the month ahead," Arwady said. "Similarly, our test positivity rate today is at 4.8%. Less than a month ago, we were at 3.8%. A full percentage point lower. We've not seen progress in that respect either."
The current numbers put Chicago in a so-called "yellow zone."
"We're in that 200 to 400 range," Arwady said. "Again, that's sort of our yellow zone where we're thinking about the need to potentially make additional changes, we would do that based on data, just as we've done all along."
The larger concern comes if the city reaches an average of 400 new cases per day, which "really marks a line in the sand," Arwady said.
According to CDPH, 400 cases per day is the equivalent of the number the state uses to determine if states should be added to the city's travel order, requiring a quarantine.
"It's the equivalent of needing to go back to a phase three, really pulling back on major activities," Arwady said last month.
And it may not be as far away as it seems.
"Regularly, we are having days with more than 300 cases," Arwady said Wednesday. "And particularly in the last two weeks, we've had a number of individual days already pushing 400 cases. And so where we're thinking about planning, needing to give a month of time, I think it is entirely possible that we would be at or very near that 400 case mark."
Arwady said the city hasn't yet determined which, if any, restrictions would be added first should metrics continue to rise. Though she indicated group gathering sizes could be on the list.
According to Arwady, much of the recent spread of the coronavirus in Chicago has been through social gatherings.
"Where we are seeing COVID spread in Chicago is in households and in social gatherings," she said Tuesday.
Arwady noted that early on in the pandemic, transmission was driven largely by congregate settings like long-term care facilities, factory-style workplaces and other areas that have since implemented new protocols and regulations to slow the spread of the virus.
But as those outbreaks have slowed, the virus has spread more rapidly in social settings that the city is unable to regulate, she said.