Estimating Undetected COVID-19 Cases in Chicago

On March 17, Chicago experienced one death due to COVID-19.  As of March 20, there were three total COVID-19 related deaths and a total of 212 confirmed cases of COVID-19 in Chicago.

With limited testing availability, the actual number of COVID-19 infected cases could be far more than the number of confirmed cases in Chicago.  Here, we estimate the actual number of COVID-19 cases by taking into account likely undetected cases.  We estimate that there may be 3,023 infected cases as of March 20, although the number of confirmed cases is at 212.

We did this estimation by using the average mortality rate at one percent, 20 days of infection to death and six days of doubling time. We used the estimation method proposed by Thomas Pueyo and Khan Academy.

A graph showing estimated COVID-19 cases in Illinois, versus actual diagnoses.

For some days, the number of confirmed cases and deaths are not available.  We also found some discrepancy between the data provided by the Johns Hopkins COVID-19 site and local news media.

We searched local media reporting and the Chicago Department of Public Health’s Chicago COVID-19 Update, published on March 19, to “fill in” to arrive at more accurate confirmed case number.

A graph showing COVID-19 positive tests in Illinois, Cook County and Chicago.

The graph above presents Illinois COVID-19 cases since January 22, 2020.

Earlier infection in Illinois were clustered in the Chicago area.  However, beginning March 15, the numbers for Cook County and Illinois increase faster than Chicago, meaning COVID-19 infections became wider spread beyond Chicago throughout the State of Illinois.

Time Series Data

Date U.S. Total IL Total Cook County Chicago Total Chicago Estimated
1/22/20 1 0 0 0 3.72
1/23/20 1 0 0 0 4.18
1/24/20 2 1 1 1 4.69
1/25/20 2 1 1 1 5.26
1/2620 5 1 1 1 5.91
1/27/20 5 1 1 1 6.63
1/28/20 5 1 1 1 7.44
1/29/20 5 1 1 1 8.35
1/30/20 5 1 1 1 9.37
1/31/20 7 2 2 2 10.52
2/1/20 8 2 2 2 11.81
2/2/20 8 2 2 2 13.26
2/3/20 11 2 2 2 14.88
2/4/20 11 2 2 2 16.70
2/5/20 11 2 2 2 18.75
2/6/20 11 2 2 2 21.05
2/7/20 11 2 2 2 23.62
2/8/20 11 2 2 2 26.52
2/9/20 11 2 2 2 29.76
2/10/20 11 2 2 2 33.41
2/11/20 12 2 2 2 37.50
2/12/20 12 2 2 2 42.09
2/13/20 13 2 2 2 47.25
2/14/20 13 2 2 2 53.03
2/15/20 13 2 2 2 59.53
2/16/20 13 2 2 2 66.82
2/17/20 13 2 2 2 75.00
2/18/20 13 2 2 2 84.18
2/19/20 13 2 2 2 94.49
2/20/20 13 2 2 2 106.07
2/21/20 15 2 2 2 119.06
2/22/20 15 2 2 2 133.63
2/23/20 15 2 2 2 150.00
2/24/20 51 2 2 2 168.37
2/25/20 51 2 2 2 188.99
2/26/20 57 2 2 2 212.13
2/27/20 58 2 2 2 238.11
2/28/20 60 2 2 2 267.27
2/29/20 68 2 2 2 300.00
3/1/20 74 3 3 3 336.74
3/2/20 98 4 4 3 377.98
3/3/20 118 4 4 3 424.26
3/4/20 149 4 4 3 476.22
3/5/20 217 5 5 3 534.54
3/6/20 262 5 5 5 600.00
3/7/20 402 8 8 8 673.48
3/8/20 518 11 11 11 755.95
3/9/20 583 15 15 15 848.53
3/10/20 959 19 19 19 952.44
3/11/20 1,281 29 29 29 1,069.08
3/12/20 1,663 39 39 39 1,200.00
3/13/20 2,179 46 46 46 1,346.95
3/14/20 2,727 64 64 61 1,511.91
3/15/20 3,499 102 102 80 1,697.06
3/16/20 4,632 105 105 103 1,904.88
3/17/20 6,421 161 161 132 2,138.16
3/18/20 7,783 288 178 147 2,400.00
3/19/20 13,677 422 278 151 2,693.91
3/20/20 19,100 585 411 212 3,023.81