The COVID Report with David Blake: Testing inadequacies
Thursday, Aug. 20
In the beginning of the pandemic, testing capacity was inadequate, and only vulnerable people and essential workers could be tested.
Since then, testing has expanded dramatically. Monday, Aug.17, I talked about how cases per fatality can be used to assess how well your area is finding infections.
https://aubellringer.wordpress.com/2020/08/17/the-covid-report-with-david-blake-cases-per-fatality/
Recently, another data scientist asked the Georgia Dept of Health for data, and they responded with a data file containing county-level data for each day, with age demographic data.
I downloaded this file and analyzed it.
You can, instead of plotting cases per fatality, simply look at the fraction of the new cases that are over age 70. That will tell you most of what you want to know about finding infections. Why is that?
Testing in people over age 70 is of high acute medical utility. It is always going to be prioritized.
Testing in people who are younger has lower acute medical utility, but just as much epidemiological utility.
We can take the ratio of new cases over 70 years old, and under, and use it. Here is a plot I made, one data point for each week in the pandemic in Georgia. I plotted this age demographic of cases vs cases per fatality.
On this plot, over most of the pandemic, Georgia was not testing enough, and cases per fatality stayed close to 10. In Georgia, 9.3% of the population is over age 70. Once the fraction of new cases over age 70 reached roughly 150% of the population fraction over age 70, the cases per fatality began to rise.
At that point, we were finding a larger percentage of infections. Around the beginning of August, we were finding 50 infections for each fatality, which means we were doing better.
To do really well, you would want to find around 200 infections for each fatality. But, 50 is much better than 10.
What is happening today is actually a little counterproductive. Since the beginning of August, younger people in Georgia have been constituting a smaller fraction of the new cases.
New cases in people over age 70 are actually rising slightly in the past three weeks, while the state has experienced a decline from the summer wave peak.
The translation here is that recovery is being underestimated. We are leaving students, both on campus, and in primary and secondary schools, to voluntarily choose whether to get tested or not.
If they test positive, they likely experience mild symptoms and have to undergo something extremely unpleasant: 10 days of isolation.
If they simply choose not to test, they skip the isolation.
In addition, there is substantial pressure at school over infection reporting. The school knows that with enough positives, they will be forced to go completely virtual.
People simply are not getting tested at the same rates, and the data show this very clearly.
This practice is being coupled with a new set of findings on children and COVID-19. Children, especially under age 10, are less likely to become infected.
However, those that are infected have virus loads indistinguishable from symptomatic adults. There is actually no relation between symptom severity and upper respiratory tract virus loads.
For this reason, it is suspected children who are infected are strong carriers of the virus without symptoms. Without surveillance testing of children, the infection can grow without being seen until adults begin to become symptomatic.
Here is a great twitter thread by an academic epidemiologist on kids and COVID-19