Earlier this month Chicago Mayor Lori Lightfoot took a page out of New York Governor Andrew Cuomo’s playbook and added a 14 day quarantine for people coming from states with a high infection COVID-19 rate.
EFFECTIVE MONDAY: To preserve the gains Chicago has made, we're issuing an Emergency Travel Order directing travelers entering or returning to Chicago from states experiencing a surge in new COVID-19 cases to quarantine for a period of 14 days. More info→ https://t.co/5D7ng691f8 pic.twitter.com/CA26uT7RF6
— Mayor Lori Lightfoot (@chicagosmayor) July 2, 2020
While NY requires just 10 COVID positive cases per 100,000 residents over a 7-day rolling average to be added to the quarantine list, Chicago requires 15 cases per 100,000 residents. NY will also add states with a 10% or higher positivity rate over a 7-day rolling average to their list, while Chicago ignores that metric.
NY currently requires a 14 day quarantine if you come from 31 states, though that is very likely to climb when the this week’s list is announced.
Based on the current COVID spike in Illinois, it’s looking probable that the state will be added to NY’s quarantine list in the near future. Yesterday’s COVID positive numbers in Illinois were 1,541, which divided by a population of 12.67MM means 12.2 positive cases per 100K residents. We’ll have to wait and see what the numbers are based on the 7 day rolling average.
Positive cases always seemed like a strange metric to use.
Ohio recently introduced a quarantine, but it’s based on states that have a testing positivity rate that exceeds 15% and not based on total cases. That seems far more sensible to me.
Why should a state be penalized for doing a lot of testing and finding more cases? What really matters is what percentage of those tests come back positive, and that’s something that won’t arbitrarily change based on how many actual tests are performed.
NY has fewer cases than CA or FL, but that’s because they didn’t do the kind of testing when they got slammed in March that is being done now.
To illustrate using very rough numbers and estimates, NY has 416K cases and 32.3K deaths. Based on the CDC’s current best estimate of an Infection Fatality Rate of 0.65%, that would mean the actual number of cases in NY was 4.96MM out of a population of 19.45MM. In NYC there were 228K cases and 23K deaths. Using that same math would impute about 3.54MM actual cases out of a population of 8.39MM. That would lend some credence to herd immunity in NY being the primary reason for the dropoff in cases there, and not the state’s action.
On the other hand, FL has 424K cases and 5.8K deaths. Using that same math would impute about 892K actual cases. Granted that FL positive case numbers are much higher currently and deaths are a trailing indicator, which will mean more total actual cases as deaths climb, but total cases is a very blunt number to use for comparison purposes.
Of course these back-of-the-envelope calculations are just rough extrapolations and not scientific data. For example, Cuomo’s numerous failures in NY likely contributed to a higher than average infection mortality rate there, which will change the math on total cases. And the CDC’s Infection Fatality Ratio best estimate is currently 0.65%, but can be anywhere from 0.5%-0.8%. But the numbers show that total cases are a poor indicator of success against COVID-19 or as a basis for quarantine.
Update: Based on a question in the comments below, I’ll try to illustrate the difference between Chicago’s quarantine list and Ohio’s quarantine list:
- Scenario 1:
- If my fictitious state of 20MM people only administered 100 tests and 90 come back positive, that’s only 90 total cases which is much less than 15 cases per 100K residents, so we would not be on Chicago’s quarantine list.
- However that would be a positivity rate of 90%, so we would be on Ohio’s more sensible quarantine list when positivity rate exceeds 15% of tests.
- Scenario 2:
- If my fictitious state of 20MM people administered 1MM tests and 3,100 come back positive, that’s more than 15 cases per 100K residents, so we would be on Chicago’s quarantine list. We would effectively be punished for administering so many tests.
- However that would be a positivity rate of just 0.3%, so we would not be on Ohio’s more sensible quarantine list.
OH quarantine map, based on test positivity rate:
Mayor Lightfoot announced today that nearby Wisconsin will soon be added to the Chicago quarantine list this week after exceeding the threshold of 15 positive cases per 100K residents.
Of course the real irony will be if Illinois exceeds the threshold of 15 positive cases per 100K residents. Based on the current trajectory, that seems like to happen over the coming weeks.
That would put the city of Chicago in the rather uncomfortable position of having to walk back the quarantine, increase the threshold, change the metric used, or look rather hypocritical if they leave things as is. After all, why should people coming from a state that exceeds 15 cases per 100K be required to quarantine if Illinois meets that threshold?
What do you think Mayor Lightfoot will do if Illinois exceeds her quarantine threshold?