What Does a Coronavirus Case Mean?
What is a coronavirus case?
The gold standard definition for a confirmed case of COVID-19 infection is a positive exam which is obtained by performing a PCR test on a cheek or nasal swab. Many states also report probable cases using a guideline put forward by the Council of State and Territorial Epidemiologists, and promoted by CDC.
Here is an example of case reporting from Delaware. Probable cases typically run about 10% of confirmed cases.
Delaware 7/8/2020
Total Cases 12,462
130.0 per 10,000 people
Confirmed Cases 11,418
Probable Cases 1,044
Other states report only confirmed cases or else report total cases without declaring whether they are only those confirmed or those confirmed plus probable.
Still other states report the total number of PCR tests that were positive. This sounds fine, but can include the same person tested more than once - or else not. Some states may include antibody results in their totals and then go on to say how many antibody tests were performed - or else not. In May, Georgia switched from reporting case totals that included antibody tests to PCR-only tests leading to a drop in their cases. It is likely that Florida is reporting both antibody positive and PCR positive together and not divulging this distinction. This functioned to keep positivity rates (positive tests/total tests) lower: antibody tests come up positive in about 60% as many instances (4.42% versus 7.53%). In an analysis I performed on seven states which provided antibody testing and antibody positive numbers, I found that antibody testing accounted for 15.4% of total testing (360,966 antibody tests/2,340,378 total tests).
All of these are mixed in with the possibility that the state just isn't telling what they are doing to derive their numbers.
The Top 20 States with the Most New Cases Per Million Population, Week Ending July 4, 2020.
Below are the weekly new cases per million population for each state and the District of Columbia from the week ending March 21 to the week ending July 4. Note that the scales vary. The states are in ranked order from 1 to 51 according to the most recent week. Each week's ranking hovers above the bar indicating the weekly case rate.
Martin Hill Ortiz is a Professor of Pharmacology at Ponce Health Sciences University and has researched HIV for over thirty years.
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