More than two-dozen people have tested positive for the coronavirus after a woman with the virus went to a Starbucks in Paju, South Korea, Bloomberg reported. But the employees of the café, who were wearing face masks, were not infected.

The outbreak, which occurred Aug. 8, is evidence of how quickly the coronavirus can spread in an enclosed area and how face masks may play a role in preventing infection.

“This speaks volumes about the role masks can play,” Ma Sang Hyuk, a pediatric infectious diseases physician at Changwon Fatima Hospital in South Korea told Bloomberg. “Masks may not provide 100% protection, but there’s nothing out there that’s as effective.”

Officials assume the coronavirus infection may have spread among patrons because they may not have been wearing face masks while eating and drinking, Bloomberg said.

“The virus may spread where people can’t wear masks while eating or drinking tea, as witnessed at the Starbucks in Paju,” Jung Eun-kyeong, head of the Korea Centers for Disease Control & Prevention, told reporters in Seoul on Sunday.

Face mask mandates are growing across the world, which has reported more than 23 million positive cases of the coronavirus and more than 800,000 COVID-19 deaths, according to Johns Hopkins University.

Seoul, which is considered a coronavirus hotspot, has imposed a face mask mandate in the metropolitan area. Government officials also are considering more stringent social distancing regulations. South Korea has more than 17,600 positive coronavirus cases and more than 300 COVID-19 deaths, data from Johns Hopkins indicated.

A Starbucks coffee cup and beans are seen in this photo taken in Washington, D.C., on Aug. 12, 2009. Paul J. Richards/AFP/Getty Images