The study, released by the Centers for Disease Control and Prevention, analyzed 314 patients and found that those who tested positive for the virus were twice as likely to have eaten at a restaurant in the previous two weeks as those who tested negative.
“We want people to understand as society opens back up where the risks are for Covid-19,” said Dr. Wesley Self, a doctor and researcher at Vanderbilt University and an author of the study.
Dr. Self said he believed in retrospect that the researchers should have made the distinction between indoor and outdoor dining.
Gov. Andrew M. Cuomo announced on Wednesday that New York City would lift its prohibition on indoor dining on Sept. 30, allowing restaurants to operate at one-quarter indoor capacity. In July, the governor and Mayor Bill de Blasio halted a plan to resume indoor dining, citing concerns about a resurgence of the virus. (The conditions of outdoor dining are considered less risky.)
Last month, data from a number of states and cities showed that community outbreaks had centered on restaurants and bars. Contact tracers in Maryland found that 12 percent of new cases in July were traced to restaurants, and in Colorado, 9 percent of outbreaks were traced to bars and restaurants. The patients in the new study were treated at 11 hospitals in California, Colorado, Maryland, Massachusetts, Minnesota, North Carolina, Ohio, Tennessee, Utah and Washington.
Some researchers have urged caution in interpreting the findings of the new C.D.C. study.
“The way folks have interpreted this study is that going to a restaurant causes Covid,” said Zack Cooper, an associate professor of public health at the Yale School of Public Health. “That isn’t what this type of study is designed to show. What this shows is people who have Covid were more likely to have been in restaurants.”
Dr. Cooper said dining in restaurants was probably associated with increased risk because it puts people in proximity with others who are not exercising caution in limiting their exposure to the virus. He said researchers needed to be careful in studying the risks of common activities, given the challenges for the general public in interpreting statistical findings.