Here’s the study behind why NYC’s mayor now recommends masks in public

New York City Mayor Bill de Blasio recently suggested that people in the city should wear face coverings, such as cloth masks or bandanas, when going out in public to try and slow the spread of COVID-19. 

De Blasio pointed Thursday to a study from Singapore released this week by the Centers for Disease Control and Prevention, which examined how presymptomatic or asymptomatic coronavirus carriers could spread the deadly virus. Researchers concluded that people who spread the virus, despite feeling healthy, could pose a threat to disease control.

“These findings also suggest that to control the pandemic it might not be enough for only persons with symptoms to limit their contact with others because persons without symptoms might transmit infection,” researchers said. 

New York state remains the epicenter of the COVID-19 pandemic in the United States, with at least 102,863 confirmed cases and at least 2,935 deaths. 

“You can create a face covering with anything you have at home right now, a piece of cloth,” de Blasio said at a news conference. “You can create your own version, you can be creative, you be creative and put your own decoration. That’s what we want you to do. Something homemade, not something professional.”

Researchers examined all 243 coronavirus cases that were reported in Singapore from Jan. 23 to March 16. They identified seven clusters of cases where presymptomatic transmission most likely occurred. 

The seven clusters occurred between Jan. 19 and March 12 and involved from two to five patients each, according to the report. Ten of the cases within the clusters could be attributed to presymptomatic transmission, and accounted for 6.4{3c4481f38fc19dde56b7b1f4329b509c88239ba5565146922180ec5012de023f} of the 157 locally acquired cases reported as of March 16, researchers added. 

“The possibility of presymptomatic transmission of [the coronavirus] increases the challenges of COVID-19 containment measures, which are predicated on early detection and isolation of symptomatic persons,” researchers said in their findings. “The magnitude of this impact is dependent upon the extent and duration of transmissibility while a patient is presymptomatic, which, to date, have not been clearly established.”

Researchers said that in four of the clusters, they determined transmission exposure occurred one to three days before the source patient developed symptoms. 

The study had three limitations, researchers said. There’s the possibility of an unknown source transmitting the virus to the clusters, recall bias could affect the accuracy of symptom onset dates, and under-detection of asymptomatic cases is possible, researchers said. 

New York City joined Los Angeles in recommending the general public wear face coverings, which officials initially said was not necessary in order to maintain supply for health-care workers. President Donald Trump and Vice President Mike Pence also said Thursday night that the CDC will issue new nationwide guidance “in the next several days” about wearing masks to prevent the spread of COVID-19. 

Read the full report from the CDC here.