CDC Guidelines Shift Amid Coronavirus Aerosol Debate

On Friday, new guidelines from CDC sought to show how the pandemic coronavirus (COVID-19) spreads. By Monday, those guidelines changed.

The initial CDC web page used language favoring aerosol transmission which includes potential suspension of respiratory droplets in the air. Now, CDC says that it had not intended to post the guidance with that particular language, which states that COVID-19 spreads via airborne particles which can suspend in the air and travel farther than 6 feet.

The CDC did not deny the possibility of airborne transmission, but instead placed a statement at the top of the guidance that their stance is presently evolving.

“A draft version of proposed changes to these recommendations was posted in error to the agency’s official website. CDC is currently updating its recommendations regarding airborne transmission of SARS-CoV-2 (the virus that causes COVID-19). Once this process has been completed, the update language will be posted,” the statement reads.

The attempt to elucidate the transmission dynamics of COVID-19 has thus far mostly highlighted the overload of information and debate the public faces when trying to follow the science of SARS-CoV-2, even among experts seeking consensus.

Infection preventionist and Contagion contributor Saskia Popescu, PhD, MPH, took to Twitter hoping to provide some clarity and nuance. See the thread below:

In terms of aerosols, droplet, & “airborne”- the best approach to communication I’ve found is that this requires enhanced respiratory protection in a healthcare setting. It’s not entirely airborne and it’s not entirely droplet, but rather something in the middle. (1/n)

— Dr. Saskia Popescu (@SaskiaPopescu) September 21, 2020

Dr. Popescu went on to state that "we know this means different things for AGMP [aerosol generating medical procedures]. For the public, I think it’s a good lesson in that the “6 ft” rule isn’t a hard rule in that there’s no magic force-field that prevents the virus from going further. Infection prevention involves multiple things simultaneously."

Another recent series of Tweets also provides key insights on the transmission dynamics of SARS-CoV-2. Muge Cevik, MD, provided a useful summary of the latest science on these dynamics in a thread accessible here:

The risk of transmission is complex and multi-dimensional. It depends on many factors: contact pattern (duration, proximity, activity), individual factors, environment (i.e. outdoor, indoor) & socioeconomic factors (i.e. crowded housing, job insecurity). (2/n) pic.twitter.com/0mEiHhbnWa

— Muge Cevik (@mugecevik) September 21, 2020

Dr. Cevik explains that "sustained close contact drives the majority of infections and clusters."

Cevik also provided surprising data on what proportion of infections are passed on.

Individual factors:

Many ppl either do not infect anyone or infect a single person, and a large number of secondary cases are caused by a small # of infected ppl. Although this also is related to other factors, individual variation in infectiousness plays a major role.(6/n) pic.twitter.com/L4vN1BgyZW

— Muge Cevik (@mugecevik) September 21, 2020

In addition, she states that "while asymptomatic patients can transmit the virus to others, emerging evidence suggests that asymptomatic index cases transmit to fewer secondary cases. Attack rates are highly correlated with symptom severity."

Overall, the debate on how SARS-CoV-2 spreads is not likely to become as clear or to-the-point as is needed for quite some time, but social media clarification via threads by health care professionals like Cevik and Popescu shows that we are able to synthesize some of these debates in order to communicate a reasonable middle ground.