(CNN) No cases of coronavirus have been linked to two Missouri hairstylists who saw 140 clients last month while symptomatic, county health officials said.
Both stylists worked at the same Great Clips location in Springfield. The clients and the stylists all wore face coverings, and the salon had set up other measures such as social distancing of chairs and staggered appointments, the Springfield-Greene County Health Department said this week.
Of the 140 clients and seven co-workers potentially exposed, 46 took tests that came back negative. All the others were quarantined for the duration of the coronavirus incubation period. The 14-day incubation period has now passed with no coronavirus cases linked to the salon beyond the two stylists, county health officials said.
During the quarantine, those who did not get tested got a call twice a day from health officials asking whether they had symptoms related to Covid-19, said Kathryn Wall, a spokeswoman for the Springfield-Green County Health Department.
"This is exciting news about the value of masking to prevent Covid-19," said Clay Goddard, the county's director of health.
"We are studying more closely the details of these exposures, including what types of face coverings were worn and what other precautions were taken to lead to this encouraging result."
In addition to the importance of masks, the case highlights how crucial contact tracing and isolation are after exposure to help stop the spread of the disease.
The salon kept impeccable records that made contact tracing possible, Goddard said.
The US Centers for Disease Control and Prevention has estimated that about a third of coronavirus infections are asymptomatic -- so it's possible some of the people may have been infected but not tested due to lack of symptoms.
But county health officials called the salon outcome encouraging, and they're using the case as a way to get additional insight on how to stop the spread of coronavirus.
And they're also reiterating the importance of masks.
One hairstylist had worked with 56 clients at the salon while the second one had seen 84 customers and seven coworkers. The stylists went to the salon for about eight days ending on May 20.
Studies have found that physical distancing and the use of a mask are the two best ways to prevent coronavirus transmission.
This month, a study published in the Lancet medical journal found people should stay six feet apart and wear face coverings. It said the chance of transmission without a face mask was 17.4%, while that fell to 3.1% when a mask was worn. The World Health Organization has urged nations to encourage the general public to wear fabric masks in areas where coronavirus is spreading.
In a statement, Great Clips said it welcomed the results.
"All customers who were tested for Covid-19 after visiting a franchised Great Clips salon in Springfield have confirmed negative test results. Together with our 1,100 independent franchisees, we care deeply about the well-being of customers, salon staff and the communities we serve, and we are grateful for the health of these individuals," it said in a statement to CNN affiliate KYTV.
More than 112,000 people have died from coronavirus in the United States, where the number of confirmed cases is more than 2 million, according to Johns Hopkins. In Missouri, the virus has killed more than 850 people and infected over 15,000 others.
The two stylists have been released from isolation, Wall said.