About three-quarters of study participants from both groups (71% of case-patients and 74% of control participants) reported having always worn a mask or cloth face covering when in public, but people who tested positive were more likely to have been in close contact with a person who also tested positive — and nearly twice as likely to have dined at a restaurant.

In short: the CDC study was testing what activities made a person more likely to contract SARS-CoV-2 and how mask-wearing and social distancing measures might influence infection rates. Having close contact with a person diagnosed with COVID-19 or going to locations that offer onsite dining was associated with a higher likelihood of being diagnosed with the disease.

“In this investigation, participants with and without COVID-19 reported generally similar community exposures, with the exception of going to locations with on-site eating and drinking options,” wrote the health agency. “Adults with confirmed COVID-19 (case-patients) were approximately twice as likely as were control participants to have reported dining at a restaurant in the 14 days before becoming ill.”

The study is not without limitations. First of all, the sample size is relatively small. Secondly, study participants self-reported their mask use, which could present an opportunity for false memories or poor recall. Participants were also aware of their infection and agreed to take part in the study, which could have influenced their responses.

Even so, the study suggests that increased infection rates among those who had dined at restaurants may be linked to air circulation. The direction, ventilation, and intensity of airflow may influence virus transmission even if social distancing measures are followed. People taking their masks off to eat and drink in closed-circulation spaces may also make them more susceptible to infection.

The findings held implications for public health, particularly as many U.S. states were partially open or allowed dine-in eating in October 2020. 

“Eating and drinking on-site at locations that offer such options might be important risk factors associated with SARS-CoV-2 infection. Efforts to reduce possible exposures where mask use and social distancing are difficult to maintain, such as when eating and drinking, should be considered to protect customers, employees, and communities,” wrote the CDC.

As of mid-October, the CDC continued to recommend that a person wear a mask whenever in public or around people who do not live in the same household. A full list of recommendations can be found here.