COVID-19 testing: the positivity rate in Europe

Date of article: 27 April 2020


Cumulative positivity rate for countries

The cumulative positivity rate for countries is calculated by dividing the total number of positive tests (or: people testing positive) by the total number of tests done (or: people tested). When the positivity rate is low, there can be many reasons. Some examples:

  • The amount of people with COVID-19 is simply low, that's why the percentage is low.
  • The testing strategy includes a mass testing programme including testing random people (e.g. this applied to UK in February 2020), lowering the percentage of positive tests.
  • The testing strategy is heavily focussing on certain parts of the population (e.g. medical personnel). This could distort the percentage either up or down.

Summarized: we should not jump to conclusions based on this type of data, but it is an interesting starting point for further analysis. Below are two lists with the current cumulative positivity rate (as of April 24th).


Current positivity rate in COVID-19 (based on samples tested, Europe)

  1. United Kingdom 23.4%
  2. Turkey 12.6%
  3. Switzerland 11.9%
  4. Italy 11.8%
  5. Finland 5.7%
  6. Iceland 4.0%
  7. Czech Republic 3.6%
  8. Slovenia 2.9%
  9. Russia 2.7%


Current positivity rate in COVID-19 (based on people tested, Europe)

  1. United Kingdom 32.3%
  2. Serbia 13.6%
  3. Portugal 10.2%
  4. Luxembourg 9.8%
  5. Denmark 6.6%
  6. Norway 4.8%
  7. Estonia 3.5%


The trend in cumulative positivity rate

Instead of the current percentage of positive tests, it's also worth looking to the trend in the positivity rate. As we have seen back in February and March when analyzing South Korea and Italy, the positivity rate was a good predictor for future reported cases. Below are two older charts which show how this worked.


Below, using data collected by Newsnodes from official government reports, we show combined charts of European countries in the period March 25th - April 24th.


Interpretation of the charts

As can be seen in the above charts, most European countries have a downward going trend in the positivity rate. Only the United Kingdom and Russia still had a rising cumulative percentage recently.

For Russia this can be explained due to their very low percentage in March when Russia had positivity rates around 0.1%; a percentage I've only seen lower in Venezuela. Looking to the daily positivity rate for Russia (4%) recently, there's nothing to worry about for Russia.

Oddly, the United Kingdom, just like Russia, started out in March with a positivity rate of around 0.2% thanks to their early warning testing program (in which they tested random people who had flu-like symptoms). Contrary to Russia however, United Kingdom has been reporting daily positivity rates of up to 50% (persons tested) throughout March/April, resulting in one the highest cumulative positivity rates of Europe (over 30%). The charts show that only in recent days the cumulative positivity rate is starting to decrease, meaning that only now the United Kingdom is starting to win the battle against the SARSCoV2 virus.

However, the most important takeaway in my opinion is that the above charts confirm the often-cited reports on new cases in Europe: Europe is definitely starting to get out of the COVID-19 woods. Only by studying charts like these, we can conclude that the decrease in new cases is not the result of less testing, but in fact less new cases being found.

article by Newsnodes








 

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