Smoke Gets in Your Eyes: How COVID Spreads Indoors

Call it the “now you see it, now you don’t, but now you see it again,” guidance about coronavirus disease 2019 (COVID-19). Recall, that on Friday, September 18, the US Centers for Disease Control and Prevention (CDC) updated its guidance on its website, stating that small aerosolized particles of the coronavirus can linger in the air and infect someone more than six feet away from the carrier. By Monday, September 25, that guidance was removed, with the CDC saying that it had been put on the website by mistake. It was still in draft form.

Well, yesterday the CDC again put the guidance on its website, acknowledging that aerosolized particles of the coronavirus can spread further than six feet and linger for a long time, particularly in poorly ventilated areas.

While reiterating that SARS-CoV-2 most commonly spreads through close contact (less than 6 feet, and for about 15 minutes) with a symptomatic or asymptomatic carrier, the CDC now suggests that the coronavirus is even more contagious than previously thought.

“Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours,” according to the updated CDC guidance. “These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space. This kind of spread is referred to as airborne transmission and is an important way that infections like tuberculosis, measles, and chicken pox are spread.”

This might not come as a surprise to many experts who’ve been closely monitoring COVID-19. Certainly not to Kevin Kavanagh, MD, a member of Infection Control Today®’s Editorial Advisory Board and a frequent contributor to ICT®. Kavanagh recently pointed out that the CDC in fact has already acknowledged that the coronavirus can be aerosolized when it released recommendations on how people should approach the upcoming holidays.

The guidance the CDC posted yesterday says that “there is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away. These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example while singing or exercising.”

Under such conditions, CDC scientists believe that aerosolized SARS-CoV-2 particles are concentrated enough to linger in the air and spread further than six feet and linger in the air.

In a posting on the blog The Conversation , Martin LaMonica likens the spread of COVID-19 indoors to someone walking into a smoky bar. If someone is smoking a cigarette outside, the air currents usually dissipate the aerosolized particles quickly, so the six-foot rule should work outdoors.

Indoors, it’s another matter.

“Very light room air currents from fans and ventilation units can transport respiratory droplets over distances much greater than 6 feet,” LaMonica writes. “However, unlike being outdoors, most indoor spaces have poor ventilation. That allows the concentration of small airborne respiratory droplets to build up over time, reaching all corners of a room.”

LaMonica adds: “It’s not surprising that most “superspreader” events that have infected large numbers of people involved indoor gatherings, including business conferences, crowded bars, a funeral and choir practice.”