Fact check: Misrepresented CDC study about community exposure to the new coronavirus

Posts on social media say a study of the U.S. Centers for Disease Control and Prevention (CDC) showed that a high percentage of people who wore masks became infected with the new coronavirus and that masks are ineffective. The results of this study, whose aim was to assess situations of community and close contact exposure, rather than the use of masks, have been misrepresented.

Reuters Fact Check. REUTERS

A post shared over 1,080 times on Facebook here  reads: “CDC Study shows 70% of coronavirus cases ALWAYS wore a mask, while only 3.9% NEVER wore a mask. If masks work, you would think those numbers would be flip flopped...”. Other examples are visible  herehere  and  here  . 

The results of the September CDC study visible  here  have also been misrepresented by media outlets and U.S. President Donald Trump. Fox News’s Tucker Carlson said the study showed that “clearly (wearing a mask) doesn’t work the way they tell us it works.” ( here ) Trump has erroneously referred to the study at least three times ( , ( ), including during his town hall on Oct. 15 ( here ).  

While the numbers mentioned in these claims are authentic (see page 3), the data is missing context. It is true that 85% of people in the study who tested positive for the coronavirus were reported to have worn a mask always or often. It is also true that mask-wearing levels were reportedly high (88.7%) among people who did not catch the virus.

Jason McDonald, a spokesman for the CDC, told Reuters via email that “the aim of the study was to assess possible situations for community exposure, not mask use.” The study, McDonald noted, found that “going to places where mask use and social distancing cannot be maintained”, like restaurants, coffee shops and bars, “might be an important risk factor for COVID-19.”

Authors of the study, which analyzed the activities of two groups of people in the 14 days prior to showing possible COVID-19 symptoms, also acknowledge that the results might not be representative of the U.S. population, as it only considered adults that had been tested in 11 health care facilities.

In total, 360 people tested for the coronavirus in July were part of the analytic sample: 154 that tested positive (case patients) and 160 that tested negative (control patients).


The data showed there was no “significant difference” when comparing indoor activities that “do not preclude mask use”, for example: both 88.6% and 88.1% of case patients and control participants respectively went shopping, 24% and 29.6% respectively went to an office.

But when looking at activities in which people could not wear masks effectively, such as eating and drinking at a public location, results showed a wider difference: 40.9% of the people who tested positive reportedly went to a restaurant, while 27.7% of the control participants went. People with the novel coronavirus who went to a dining place, bar or coffee shop were also “less likely to report observing all [other] patrons” at the establishment “adhering to recommendations such as wearing masks or social distancing.”

The study also found that close contact, defined as within 6 feet for more than 15 minutes, with a person carrying the virus plays a substantial role in the spread the disease: 14% who tested negative reportedly had a close contact, 42% of those who tested positive did.


McDonald added that the CDC has clearly stated that “that wearing a mask is intended to protect other people in case the mask wearer is infected, rather than the wearer (  here ). 

Health authorities have never said masks alone will slow the spread of the coronavirus, but have an impact when combined with other prevention methods, such as hand washing and social distancing ( herehere ). Evidence that masks significantly help to reduce the risk of infection is visible  here , and  here .  

Reuters has debunked other misleading claims about face coverings  here  ,  here  and  here


Missing context. Both groups of people with and without the novel coronavirus, demonstrated high levels of mask use (85% and 88.7% respectively). The study, which aimed to analyze community and close contact exposure and not mask use, found that more infected people had been to locations where masks cannot be worn effectively, like restaurants and bars.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts  here  .