Tuesday, March 24, 2020

Accelerating infection rates? Or accelerated testing?

Accelerating infection rates? Or accelerated testing?

It appears the spread of COVID 19 is not accelerating as the media suggests. The increase in confirmed cases is a result of accelerated testing.

According to data shared by the Atlantic on March 17, only 25,000 Americans had been tested for COVID 19 resulting in 4,400 confirmed infections by March 12. That suggests a 17.6% infection rate per tested specimens. This infection rate very likely over-estimates the infection rate of the American population, as most tests are performed on people concerned about respiratory symptoms that could also be caused by the common cold or the flu. Likewise younger people who are less likely to get infected are unlikely to seek testing.

If the pandemic spread is accelerating, then infection rates per test should be increasing. But they are not according to my calculations.

The Atlantic provided access to a data base listing the number of COVID 19 tests for each state.
Not all states had reported, but as of March 23, the number of tests had accelerated to 317,240 total. Based on the current number of confirmed cases, 49,940, the number of cases per test was just 15.7%. At the very least, the smaller percentage of confirmed cases per test suggest there has been no acceleration in the spread of the disease. Journalists reporting on the spread of COVID 19 should not just report the number of confirmed cases but the number of cases per the number of tests.

Because many confirmed cases have only mild symptoms, the mortality rate is also informative. Of the currently confirmed 49,940 American cases, there have been 634 deaths. That is a mortality rate of less than 1.3% of confirmed cases. For comparison, the death rate for the closely related SARS virus was over 9%, but there were far fewer infections. The COVID19 death reate is ten times greater than influenza. However since October 2019, many more people are infected by the flu, over 38 million,  and the number of deaths is estimated between  23,000 and 59,000, far greater than COVID 19.

If COVID 19 behaves like the flu, then warming weather should cause infections to drastically decline as we progress toward summer