Researchers say that conversation is the ‘dominating’ form for transmission, while wearing masks can reduce risk of infection eightfold.
BETHESDA, Md. — Cover your mouth — when you talk? That’s the suggestion by some doctors, at least during the coronavirus pandemic. Alarming new research claims that chatting is more likely to spread the virus that causes COVID-19 than coughing or sneezing.
Conversations with friends, family, colleagues or other members of the community pose the greatest danger, researchers say. They suggest that masks should be worn in offices, shops, vehicles and other confined spaces. This can reduce risk of infection more than eightfold — if both individuals are covered.
Tiny aerosols of the virus emitted when speaking linger in the air for longer than larger droplets from a cough or sneeze. Researchers say their review shows “solid evidence” that talking is the “dominating” source for transmission.
“We have all seen some spit droplets flying when people talk, but there are thousands more, too small to be seen by the naked eye,” says senior author Dr. Adriaan Bax, a chemical physicist at the National Institutes of Health, Bethesda, Maryland, per South West News Service. “When the water evaporates from such speech generated, potentially virus rich droplets, they float in the air for minutes, like smoke, thus putting others at risk.”
The review in the Journal of Internal Medicine shows that size really matters when it comes to spreading Covid.
“Respiratory droplets emitted while breathing, speaking, singing, coughing and sneezing span a continuum of sizes that depend on their generation mechanism and their site of origin,” explains Bax.
Large droplets fall to the ground over short distances because they are heavier. They play a “relative small role in transmission.” Meanwhile, smaller droplets, known as aerosols, can carry the virus more than six-and-a-half feet and linger.
Of most concern is the large fraction of speech aerosol that is intermediate-sized because it remains suspended in air for minutes and can be transported over considerable distances by convective air currents.
“The abundance of this speech-generated aerosol, combined with its high viral load in pre- and asymptomatic individuals, strongly implicates airborne transmission of SARS-CoV-2 through speech as the primary contributor to its rapid spread,” says Bax.
The infection commonly starts in the nose and throat, or upper respiratory tract (URT). It can migrate to the lungs, the lower respiratory tract (LRT) and other organs, often with severe consequences. Infection in the lungs can lead to shedding the virus through breath and cough droplets. But the nose and throat, where the coronavirus enters the body through inhalation, enables it to be spread through speech droplets.
Moreover, the viral load can be high in carriers with mild or no symptoms, such as young people and schoolchildren.
“The acoustic waves generated during vocalization involve high-speed passage of air pressurized by the lungs past the mucosal epithelial layers of the vibrating vocal folds,” explains Bax. “These sounds are further modulated when air travels through narrow passages between the tongue, lips and teeth. For example, enunciation of ‘p’ and ‘b’ involves parting of the lips, whereas ‘t’ involves transient contact of the tongue and teeth. As these surfaces part, a fluid filament or film is formed between them. Air rushing by can break the filament or burst the film with the fluid fragmenting into droplets that join the airstream. Droplets generated in the oral cavity consist mostly of saliva and span a range of sizes comparable in quantity and size to those generated by coughing and sneezing.”
Catching Covid depends on a range of factors including how much of the aerosol is breathed in, whether it is indoors, levels of ventilation and the distance between the people involved.
“Unmasked speech in confined spaces represents the activity that poses the greatest risk to others. Since eating and drinking often take place indoors and typically involve loud speaking, it should come as no surprise that bars and restaurants have become the epicenter of multiple recent superspreading events,” the review reads. “Next to vaccination, mitigation strategies should emphasize the use of face masks when speaking and ensuring adequate ventilation to flush out long-lived aerosols that might otherwise accumulate in closed environments and enhance the risk of more serious LRT infections.”
The authors say that wearing of face coverings to limit the spread of respiratory viruses began in the east decades ago — and we should embrace what they have taught us.
SWNS writer Mark Waghorn contributed to this report.