There's an article circulating on Czech social media that makes the following interesting claim, among others (translation mine):

Data that we currently have available say that in areas where SARS or MERS was active, there are now tens of percent of people who have come into contact with it. In total this means millions, or more likely tens or hundreds of millions of people. I remind you that in official statistics, only thousands of cases were reported.

Do we now have data that support the fact that this many people have been infected by SARS?

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    There obviously are such statistics, but an extra page on the web in English on this probably won't help much the Czechs who just believe/read their own-language press/websites... Also "in contact" (your translation of the claim) is not the same as "infected" (your q title). – Fizz Mar 30 '20 at 15:38
  • I don't know any Czech, so the article didn't help me much, but is there a reason behind the claim that the official numbers (e.g. WHO stats) are off by 2-3 orders of magnitude? – HDE 226868 Mar 30 '20 at 15:40
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    I believe the idea is that the virus is much less lethal and most infections are asymptomatic or mild illness, and/or the virus mutated in a much less lethal form. – Petr Hudeček Mar 30 '20 at 16:39


The premise behind the article seems to be that SARS was widely prevalent (in some areas), >10% of people were infected, without severe symptoms, and developed antibodies that can now be tested for.

A 2006 systematic review looked at this:

Our meta-analysis, which included all identified studies except those on wild animal handlers, yielded an overall seroprevalence of 0·10% [95% confidence interval (CI) 0·02–0·18]. Health-care workers and others who had close contact with SARS patients had a slightly higher degree of seroconversion (0·23%, 95% CI 0·02–0·45) compared to healthy blood donors, others from the general community or non-SARS patients recruited from the health-care setting (0·16%, 95% CI 0–0·37).

This figure of 0.16% is in stark contrast to the claimed "tens of percent".

Although there are considerable variations in the seropositive estimates reported, it is clear that seroconversion is extremely rare among health-care workers, close contacts of SARS patients who did not develop the disease and members of the general population, including healthy individuals and non-SARS patients. This property of SARS-CoV, perhaps reflecting the evolutionary fitness of the virus, is in stark contrast to other common respiratory agents, most notably influenza where the usual ‘iceberg’ concept of disease applies. Instead the pattern of SARS infection in the community can paradoxically be represented as an inverted iceberg.

Iceberg concept of disease, inverted

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    Do I need to explicitly state that this is about SARS-CoV: The Original, not SARS-COV-2, behind COVID-19? – Oddthinking Mar 31 '20 at 1:12
  • The quoted claim in the question is also about MERS, which can be considered a canon part of the trilogy ... – Hagen von Eitzen Mar 31 '20 at 15:21
  • @HagenvonEitzen: The quote says it is true of both diseases, but the question from the OP was explicitly about SARS, as was the research. – Oddthinking Mar 31 '20 at 17:14

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