In January, at a restaurant in Guangzhou, China, one diner infected with the novel coronavirus but not yet feeling sick appeared to have spread the disease to nine other people. One of the restaurant’s air-conditioners apparently blew the virus particles around the dining room.

There were 73 other diners who ate that day on the same floor of the five-story restaurant, and the good news is they did not become sick. Neither did the eight employees who were working on the floor at the time.

Chinese researchers described the incident in a paper that is to be published in the July issue of the Emerging Infectious Diseases, a journal published by the Centers for Disease Control and Prevention. The field study has limitations. The researchers, for example, did not perform experiments to simulate the airborne transmission.

That outbreak illustrates some of the challenges that restaurants will face when they try to reopen. Ventilation systems can create complex patterns of airflow and keep viruses aloft, so simply spacing tables six feet apart — the minimum distance that the C.D.C. advises you keep from other people — may not be sufficient to safeguard restaurant patrons.