The Centers for Disease Control and Prevention (CDC) estimate of the risk of COVID-19 transmission outdoors is misleading, public health experts warn.
When the federal health service released new guidelines on masks for fully vaccinated people last month, director Dr. Rochelle Walensky stated that ‘less than 10 percent’ of the spread of the coronavirus took place outdoors.
Infectious disease epidemiologists and scientists tell DailyMail.com that while the figure is not incorrect, the actual risk is believed to be much lower.
The number of COVID-19 cases associated with outdoor spread is less than one percent, and can be as low as 0.1 percent.
It comes as New York Times critic David Leonhardt criticized the agency on Tuesday using mis-characterized data – from surveys at construction sites in Singapore – to tell Americans to keep their masks out rather than pursue other interventions to lower infections.
Last month, the CDC said that “ less than 10% ” of all coronavirus transmission occurs outdoors. Pictured: Guests stop to take a selfie at Magic Kingdom Park at Walt Disney World Resort, July 2020
Several public health experts claim the true risk of outdoor spread is believed to be less than 1%, and possibly as low as 0.1% (above)
Before the CDC released its estimate last month, officials had not provided a concrete number about the risk of outside transmission.
But according to The Times, when the agency settled for “ less than 10 percent, ” the investigation cited that a large proportion of COVID-19 cases contracted from outside occurred at construction sites in Singapore.
For example in one study from the London School of Hygiene & Tropical Medicine, 95 of the 10,926 documented cases worldwide were classified as outdoors.
All 95 were linked to a cluster at a construction site in Singapore.
The data comes from the Singapore Ministry of Health, but officials there do not classify the cases as ‘out-of-home transmission’.
“We have not classified it outside or inside,” spokesman Yap Wei Qiang told The Times.
“It could have been a workshop transfer where it happens outside on the construction site, or it could also have happened indoors on the construction site.”
The Times found that in many cases the workers had been in close contact with each other and met or eaten in enclosed outdoor areas.
In addition, several of the locations that researchers defined as outdoors for their academic papers were in fact a mix of indoors, outdoors and outdoors, meaning that many of the broadcasts in Singapore could have taken place indoors as well.
But even if all cases in Singapore were classified as outdoor transmission, that still represents less than one percent of the total number of cases.
In another study, in the Journal of Infectious Diseases, researchers conducted a systematic review of the cases in Singapore and others around the world, and state that they found that the proportion of global infections occurring outdoors is less than 10 percent.
“They write in the paper that there is limited data, but certainly less than 10 percent,” Dr. Aaron Richterman, an infectious disease physician at the University of Pennsylvania, told DailyMail.com.
‘You don’t want to exaggerate a claim in scientific journals, so that’s probably where the 10 percent came from.
‘That 10 percent was then translated into the supervision, although if you look at it, that is much less than one percent.’
Other studies, such as a from Wuhan, China, found that only one of 7,324 infections was related to outdoor transmission.
Another, from Ireland, found one case of COVID-19 in every 1,000 traced to outdoor spread.
“There has been an overwhelming amount of studies on the risk factors of transmission and transmission patterns,” said Richterman.
And there really aren’t any well-documented incidental handover cases like another person [transmitting the virus by] walking by another person on the street. ‘
Richterman said the CDC’s guidance had led to a diversion of interventions that could actually help lower the number of cases.
“That’s where you have circumstances where someone on the street wears a mask, walks into a restaurant to meet a friend, and takes off the mask to sit down for dinner,” he said.
“And the second event has a much greater risk of transmission.”
In the Times article, Leonhardt also stated that the CDC’s “exaggeration” about the risks of outside transmission has led to confusion about what activities are dangerous.
“All the while, the scientific evidence points to a conclusion far simpler than the CDC’s message: masks make a huge difference indoors and rarely matter outdoors,” he wrote.