Public health experts say COVID-19 cases that spread outdoors as low as 0.1 percent of all cases

The Centers for Disease Control and Prevention’s (CDC) estimate of the risk of COVID-19 transmission outdoors may be misleading, public health experts warn.

When the federal health agency released new guidelines on masks for fully vaccinated people last month, director Dr Rochelle Walensky stated that ‘less than 10 percent’ of coronavirus spread was occurring outside. Epidemiologists and infectious disease scientists tell Daily Mail that although the figure is not incorrect, the true risk is believed to be much lower. The number of COVID-19 cases linked to outdoor spread is below one percent, and may even be as low as 0.1 percent.

New York Times critic David Leonhardt criticized the agency on Tuesday using mischaracterized data – from studies at construction sites in Singapore – to tell Americans to keep their masks on outside rather than following other interventions to help drive down infection rates. Prior to the CDC releasing its estimate last month, officials had not stated a concrete number on the risk of outdoor transmission. But, according to The Times, when the agency did settle on “less than 10 percent,” it cited studies showing a large share of COVID-19 cases contracted outside occurred at construction sites in Singapore [Reason].

For example, in one study from the London School of Hygiene & Tropical Medicine, 95 cases out of 10,926 documented around the world were classified as outdoors. All 95 were linked to a cluster at a building site in Singapore. The data comes from Singapore’s Ministry of Health, but officials there don’t classify the cases as ‘outdoor transmission.’ “We didn’t classify it according to outdoors or indoors,” spokesman Yap Wei Qiang told The Times. “It could have been workplace transmission where it happens outdoors at the site, or it could also have happened indoors within the construction site.”

The Times discovered that, in many of the cases, the workers had been in close contact with each other and had either met or eaten in enclosed outdoor spaces. What’s more, several locations that researchers had defined as outdoors for their academic papers were actually a mix of indoors and outdoors as outdoors, meaning many of the Singapore transmissions could have actually occurred inside. However, even if all the Singapore cases were classified as outdoor transmission, that still represents fewer than one percent of the total cases.

In another study, in the Journal of Infectious Diseases, researchers conducted a systematic review of the cases in Singapore and other around the world, and states they found that the proportion of global infections that occurred outdoors is below 10 percent. “In the paper, they write there is limited data but certainly less than 10 percent,” Dr Aaron Richterman, an infectious disease physician at the University of Pennsylvania, told Daily Mail. “You don’t want to overstate a claim in academic journals, so that’s probably where the 10 percent figure came from. That 10 percent then got translated to the guidance, even though when you look at it, it’s much less than one percent” [Newsweek].



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