Recently I've heard in one interview with a Professor of Epidemiology, that in my country the epidemic curve of COVID-19 is not flattened (contrary to popular opinion), but rather is truncated at the level of diagnostic efficiency. He argued, that this phenomenon is caused by too few tests being performed. Could you explain, why it might be the case?

  • it may be the case for your country, which is? Commented Jun 1, 2020 at 21:06
  • Poland. And I'm a little bit confused, because from what I've seen the number of tests isn't so small (or maybe I don't have a good reference point). Commented Jun 1, 2020 at 21:24

1 Answer 1


The epidemic curve depends on diagnostic methods and definitions. If your case definition requires a positive rt-PCR without typical clinical symptoms, and you don't do enough testing, then it will appear that your epidemic curve is flattening whereas you are only diagnosing symptomatic and severe cases.

In an extreme example Wuhan had thought they had virtually eliminated the virus

Wuhan, which had only five active cases as of Friday, used a number of different methods to assess everyone, from diagnostics that look for active infections to antibody measurements that detect markers in the blood for exposure to the coronavirus. Makeshift tents were set up in residential compounds across the city to swab throats or noses with the results likely to be closely watched internationally given China’s position as the first major economy to emerge from COVID-19 lockdowns.

but on recent retesting of the 11 M population they have picked up 206 asymptomatic cases so far. Those asymptomatic cases could cause the epidemic to flare up at any time so it's not curve flattening at all.

As of Saturday, the central Chinese metropolis had conducted 6.68 million so-called nucleic acid tests (NATs) and discovered 206 asymptomatic cases across more than 10 districts, according to notices from the municipal health commission. Disease control authorities announced the initiative on May 11, making Wuhan, where the pandemic erupted last year, the first major Chinese city to roll out mandatory mass testing.



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