The Scale of Testing Compared to the Scale of the Outbreak

Fox News, Trump (and Zeldin) are blaming the current resurgence of Covid-19 cases on increased testing.  So let’s have a look at the data!  I highly recommend this website: https://ourworldindata.org/coronavirus-testing. The following graphs come from this site which has data for most countries in the world.  Clearly, increased case numbers most often do not correlate with increased testing!

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The above graph depicts daily tests per million inhabitants (Y-axis) versus daily confirmed cases of Covid-19 (X-axis).  The line traces the data over time (April 8th to June 26th).  In this case, it is data for Luxembourg.  Note that the daily tests per million remained constant from April 8th through June 1st while confirmed cases dropped about 100-fold. And then the daily tests performed rose by nearly tenfold (May 20 through the end of June), but the confirmed cases rate remained more or less constant. In other words NO CORRELATION between testing numbers and confirmed cases.

Let’s look at some other countries.

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In Bolivia there has been a steady increase in testing and likewise a steady increase in confirmed cases.  But note that the positive rate (light grey diagonal lines) has gone from 10% in March to 50% in June.  If the increase in confirmed cases were solely due to increased testing, the positive rate should remain constant.  NB: the ‘positive rate’ is the percentage of tests that are positive over the total number of tests performed.

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In Marocco testing increased by about 10-fold between April 21 and May 30. But the confirmed cases decreased from 5/Mio people to about 1/Mio people and the positive rate fell from 20% to 0.5%! In June there was a sharp rise in confirmed cases but daily test numbers remained constant.  Again: NO CORRELATION.

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The USA shows a similar pattern to Marocco: initially a steady rise in both confirmed cases and testing.  Then in April testing increases steeply, but confirmed cases actually diminish, and in June there appears to be a rise in confirmed cases but testing remains constant.   NO CORRELATION.

These curves indicate that increased testing is hardly the sole factor when trying to explain increased confirmed cases.  In fact, there is no evidence that increased testing plays any role.  More likely, it is a number of factors that leed to rising case numbers.  These would include “opening up” prematurely, non-adherence to public health rules, such as social distancing, hand washing, wearing masks, and avoiding mass gatherings (especially indoors).

Visit the website to view the results in your favorite country!

This is a great article on the frequency of testing and the lag in test reporting in the US and why it is so important for contact tracing!

About D. Posnett MD

Emeritus Prof. of Medicine, Weill Cornell Medical College
This entry was posted in Coronavirus, Health Care, public health, Trump, Uncategorized, Zeldin and tagged , , , . Bookmark the permalink.

1 Response to The Scale of Testing Compared to the Scale of the Outbreak

  1. Pingback: Pandemic: How did Trump’s America Screw up? | Resist and Replace

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