CSU COVID 19 is Primarily Spread by Airborne Particles Droplets Discussion
Based on study and the reporting of the news article regarding the Singapore study only, can the researchers conclude that COVID-19 is spread mainly through the air in fine droplets (that may stay suspended for hours) rather than in larger droplets that quickly fall to the ground and contaminate surfaces? Why or why not? INDEPENDENT JOURNALISM SINCE 1921
HEALTH & MEDICINE
New studies hint that the coronavirus may be evolving to become
The virus appears to spread through the air, but masks reduce the amount of infectious virus
A researcher demonstrates the use of a device that captures fine aerosols and large droplets in a person’s breath exhaled while breathing,
talking and singing.
NATIONAL UNIVERSITY OF SINGAPORE
By Tina Hesman Saey
AUGUST 17, 2021 AT 3:48 PM
Small aerosol particles spewed while people breathe, talk and sing may contain more coronavirus than
larger moisture droplets do. And the coronavirus may be evolving to spread more easily through the air, anew
study suggests. But there is also good news: Masks can help.
About 85 percent of coronavirus RNA detected in COVID-19 patients’ breath was found in fine aerosol
particles less than five micrometers in size, researchers in Singapore report August 6 in Clinical Infectious
Diseases. The finding is the latest evidence to suggest that COVID-19 is spread mainly through the air in
fine droplets that may stay suspended for hours rather than in larger droplets that quickly fall to the
ground and contaminate surfaces.
Similar to that result, Donald Milton at the University of Maryland in College Park and colleagues found
that people who carried the alpha variant had 18 times as much viral RNA in aerosols than people infected
with less-contagious versions of the virus. That study, posted August 13 at medRxiv.org, has not been yet
been peer-reviewed. It also found that loose-fitting masks could cut the amount of virus-carrying aerosols
by nearly half. In one experiment, the Maryland team grew the virus from the air samples in the lab. That
could beevidence that may convince some reluctant experts to embrace the idea that the virus spreads
The debate over aerosol transmission has been ongoing since nearly the beginning of the COVID-19
pandemic. Last year, 200 scientists wrote a letter to the World Health Organization asking for the
organization to acknowledge aerosol spread of the virus (SN: 7/7/20). In April, the WHO upgraded its
information on transmission to include aerosols (SN: 5/18/21). The U.S. Centers for Disease Control and
Prevention had acknowledged aerosols as the most likely source of spread just a few weeks before.
Previous studies in monkeys have also suggested that more virus ends up in aerosols than in large droplets.But
some experts say that direct evidence that the virus spreads mainly through the air is still lacking.
“There’s lots of indirect evidence that the airborne route — breathing it in — is dominant,” says Linsey
Marr,a civil and environmental engineer at Virginia Tech in Blacksburg, who studies viruses in the air. She
was one of the 200 scientists who wrote to the WHO last year. “‘Airborne’ is a loaded word in infection
control circles,” she says, requiring health care workers to isolate patients in special rooms, wear
protective equipment and take other costly and resource-intensive measures to stop the spread of the
disease. For those reasons, infection control experts have been reluctant to call the coronavirus airborne
without especially strong proof.
Most COVID-19 cases have been among close household contacts — typically within the 6-feet splash
zone of large droplets. It can be hard to tease out whether such infections were passed on by large droplet
contamination or by breathing the same air. But for other situations, such as when patrons get infected
while sitting across a restaurant from someone with COVID-19, aerosols are really the only explanation,
Mechanical engineer Kwok Wai Tham of the National University of Singapore set out to sample how much
virus COVID-19 patients produce when they breathe, talk or sing, in part, to address skeptics’ concerns.
“I’m doing this to convince some very close friends,” he says. He and colleagues rolled a mobile lab into 22
patients’ rooms and had volunteers stick their heads into a large metal cone.
The researchers collected both aerosols and larger droplets that the patients exhaled while breathing
quietly for 30 minutes, while repeating passages from Dr. Seuss’ Green Eggs and Ham for 15 minutes, or
while singing simple tunes like the “Happy Birthday” song, “Twinkle, Twinkle Little Star” or the “ABCs”
for 15minutes. The scientists tested both aerosols and large droplets in the air samples for coronavirus RNA
and calculated how many copies of the virus’s nucleocapsid protein gene, or N gene, were present. That
gives an estimate of how much virus is in a sample.
Of the 22 patients who sang for science, only 13 spewed forth detectable levels of viral RNA. In general,
singing created the most virus-laden aerosols, but some people generated more while talking. Those
differences might be attributable to the volume at which volunteers sang, Tham says. “Some people were
shy and sang softer. Others were quite uninhibited.
The overall amount of virus that people produced varied widely. Scientists already knew that some peopleare
more likely to spread the virus than others, including some people involved in superspreading events (SN:
6/18/20). In this new study, the differences weren’t due to symptoms — some asymptomatic people made
more virus than those with fevers, coughs or runny noses.
Only one factor stood out as affecting the amount of virus emitted. People who were earlier in the course
of infection tended to produce more virus, the researchers found. That agrees with data from lab animal
studies and other human studies suggesting that people are most contagious in the first week after
catching the coronavirus (SN: 3/13/20).
So far, Tham’s skeptical virologist friends aren’t convinced that he’s demonstrated that aerosol
transmission is the major route of COVID-19 spread. “They say, ‘we need the golden evidence. Show me a
live virus that is retrieved from the air,’” Tham says.
Viral RNA could be debris from dead viruses that can’t cause infection, says Andrew Pekosz, a virologist at
the Johns Hopkins Bloomberg School of Public Health who was not involved in either study. “In the
absence of infectious virus, the significance of aerosols on transmission is still a bit unclear.”
The study from the Maryland group may provide that evidence. In that study, people with
asymptomatic or mild coronavirus cases recited the ABCs, shouted “Go Terps!” (the Maryland mascot)
or sang “Happy Birthday” into a similar device. In this study, the infected people did the activitiesonce
while wearing a mask and once while not wearing one.
About 45 percent of fine aerosol particles contained viral RNA, as did 31 percent of coarse aerosols largerthan
5 micrometers and 65 percent of swabs collected from the volunteers’ mobile phones, the researchers found.
(In medical research, objects such as phones that can carry disease-causing organismsare known as fomites.)
In addition, the increased amount of alpha variant in aerosols may suggest that the coronavirus is evolving
toward more efficient airborne spread, the researchers propose. The study was done from May 2020 to
April 2021, before the delta variant began its surge in the United States.
Researchers were able to grow infectious virus from two of 66 aerosol samples, both collected while
people were wearing masks. None of the coarse aerosols or phone swabs yielded any infectious virus.
Although the Maryland group used an efficient way to look for infectious virus in aerosols, it was still rare
to find them, Pekosz says. “It would be difficult to make the case that this was what is responsible for
increased spread of alpha.”
But Marr says the data do suggest the coronavirus is evolving toward more efficient spread through the air.
Although the study involved only four patients infected with alpha, those people consistently released
more virus than people infected with other variants. “These results combined with epidemiological
observations about the spread of alpha, and now delta, support the idea that these variants are
supercharged when it comes to aerosol transmission,” she says.
The masks volunteers wore in the Maryland study were mostly loose-fitting. They ranged from a singlelayer homemade cloth mask early on and progressed over the course of the study to double-layer
commercially made cloth masks, to double masks, surgical masks and one KN95 mask by the end. On
average, the masks reduced the number of virus-containing, coarse aerosols produced by 77 percent
compared with no mask. And virus-laden fine aerosols were reduced an average of 48 percent, though the
reduction ranged from 3 percent to 72 percent. Masks performed equally well against the alpha variant as
for other variants. Previous studies have suggested that well-fitting masks — ones that seal tightly to the
face and don’t leave gaps at the tops, bottoms or sides for the virus to pass unfiltered — may reduce
coronavirus exposure by 96 percent if everyone is wearing them (SN: 2/12/21).
The latest results suggest that masks can help reduce the amount of virus people give off, though the
coronavirus can still escape if the face coverings are worn loosely. “With the dominance of newer, more
contagious variants than those we studied, increased attention to improved ventilation, filtration, air
sanitation, and use of high-quality tight-fitting face masks or respirators … will be increasingly important
for controlling the pandemic,” the researchers wrote. That’s especially important in places with low
Editor’s Note: This story was updated August 25, 2021, to correct the definition of a fomite. It is an object or surface that can carry diseasecausing organisms or viruses. Fomites are not a type of respiratory droplet.
A version of this article appears in the September 25, 2021 issue of Science News
• K.K. Coleman et al Viral load of SARS-CoV-2 in respiratory aerosols emitted by COVID-19 patients while breathing, talking,
and singing. Clinical Infectious Diseases. Published online August 6, 2021. doi: 10.1093/cid/ciab691.
• O.O. Adenaiye et al Infectious SARS-CoV-2 in exhaled aerosols and efficacy of masks during early mild infection.
medRxiv.org. August 13,2021. doi: 10.1101/2021.08.13.21261989.
Excerpts from the Research Article
K.K. Coleman et al Viral load of SARS-CoV-2 in respiratory aerosols emitted by COVID-19 patients while breathing, talking, and singing.
Clinical Infectious Diseases. Published online August 6, 2021. doi: 10.1093/cid/ciab691.
Patient Recruitment and Data Collection
Participants were recruited from February through April 2021 at the National Centre for Infectious Diseases in
Singapore. During this outbreak phase, as per national public health policy, all persons in Singapore with
confirmed SARS-CoV-2 infection, regardless of symptom or clinical status, were admitted for inpatient isolation
and evaluation before transfer to designated isolation facilities. All newly admitted patients were screened based
on the following inclusion criteria: age 21 years or older and positive for COVID-19 via reverse transcription–
quantitative polymerase chain reaction (RT-qPCR). Basic demographic data were recorded. Symptom data were
collected based on a list of 7 prespecified symptoms. For asymptomatic individuals, the day of diagnosis was
recorded as day 1 of illness. Cycle threshold (Ct) values of clinical respiratory samples and SARS-CoV-2
serology test results were obtained from medical records. Virus genome sequence data were obtained from
National Public Health Laboratory records. This study was approved by the National Healthcare Group Domain
Specific Review Board, reference number 2020/01113. Written informed consent was obtained from all study
Twenty-three patients were enrolled in the study, including 1 patient who withdrew before sample collection.
Among the 22 remaining participants, 19 (86%) were male, with a median age of 38 years (range: 23–66 years).
Five (23%) were asymptomatic (never developed symptoms). Thirteen (59%) emitted detectable levels of SARSCoV-2 RNA in respiratory aerosols (Table 1), including 3 asymptomatic patients and 1 presymptomatic patient.
SARS-CoV-2 copies emitted per expiratory activity per participant (30-minute breathing, 15-minute talking, or
15-minute singing) ranged from 63 to 5821 viral N gene copies. Age, sex, virus variant type, clinical symptoms,
presence of SARS-CoV-2 antibody at diagnosis, and Ct value of clinical sample at diagnosis were not
significantly different between patients with and without detectable viral RNA in respiratory aerosols (Table 2).
However, the median day of illness was significantly different: patients with detectable viral RNA in aerosols
were earlier in the course of illness (median day of illness: day 3 vs day 5; P = .025). The highest emitters
(participants 12 and 16) were sampled on day 3 of illness and accounted for 52.4% of the total viral load captured
in our study.
Fine aerosols (≤5 μm) produced by talking and singing contain more SARS-CoV-2 than coarse aerosols (>5 μm)
and may play a significant role in SARS-CoV-2 transmission. Thus, exposure to fine aerosols should be
mitigated, especially in indoor environments where airborne transmission of SARS-CoV-2 is most likely to occur.
While patients with COVID-19 early in the course of illness are likely to shed detectable levels of SARS-CoV-2
RNA in respiratory aerosols, culturing SARS-CoV-2 from these patient aerosol samples remains challenging.
Person-to-person variation in virus emission is also high. Careful focus is needed on sampling methodology and
duration, infectiousness of patients during sampling, and virus culture methodology. Whether isolating viable
virus in respiratory aerosols can be more easily accomplished from sampling patients infected with emerging
SARS-CoV-2 variants is an urgent enquiry for future investigations. Reducing airborne transmission by altering
or averting direct airflow exposure in singing and speech situations indoors may be important practical options to