COVID Archives

Daily COVID model update for Sunday, April 19

National growth rate falls to new low of 4.0%

The news today is better. The national growth rate fell from 5.2% to 4.0%. We witnessed a small reversal in the trend of the data the past few days. Some of it was the reclassification of data by NYC, but it was more widespread than that. As of April 14, the CDC changed the definition of a “case”. Here’s an excerpt from the CDC website:

2. As of April 14, 2020, CDC case counts and death counts include both confirmed and probable cases and deaths. This change was made to reflect an interim COVID-19 position statementpdf iconexternal icon issued by the Council for State and Territorial Epidemiologists on April 5, 2020. The position statement included a case definition and made COVID-19 a nationally notifiable disease.

A confirmed case or death is defined by meeting confirmatory laboratory evidence for COVID-19. A probable case or death is defined by i) meeting clinical criteria AND epidemiologic evidence with no confirmatory laboratory testing performed for COVID-19; or ii) meeting presumptive laboratory evidence AND either clinical criteria OR epidemiologic evidence; or iii) meeting vital records criteria with no confirmatory laboratory testing performed for COVID19.

You’ve probably seen the headlines about the spike in COVID deaths, but this is caused by data redefinition, and doesn’t mean that the disease is suddenly accelerating. As we saw a couple of weeks ago when the case definition was last expanded, the case count grew at a faster rate for a few days, then settled down to the previous pattern. I believe we’ll see the same thing this time. This does make modeling more difficult without consistent case definitions. I’ve experienced this in the past during the AIDS epidemic. There was a constant widening of the definition of an AIDS case, and part of our job was to figure out how much was actual growth and how much was reclassification. I’m not even attempting that here. I’m just letting the data flow through, and doing my best to explain it.

In other news, I did re-parameterize my Logistic model yesterday. This fit is not as tight as the last fitting, and my theory is that in fact, the progression has slowed over the past couple of weeks as a result of societal behavioral changes. This is probably of more interest to me than to you, but I’ll use the newly refitted model in the graphs where I’ve contrasted to model numbers.

As always, if you have any questions about my assumptions, or how I’m modeling, or want to know about Logistic modeling generally, drop me a line.

  • Likely date of active case peak (Chalke modeling): April 10
  • Likely date of peak deaths (IHME): April 15 (last revision on April 17)
  • Short term projection for tonight: 770,000
  • Total Test Results reported yesterday: 149,114
  • Total Pending tests reported yesterday: 9,906 (new low)
  • National reported case Growth Rate yesterday: 4.0% (new low)

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