How the CDC Flubbed Its Messaging on COVID Transmission

What explains the reluctance to come right out and acknowledge that we appear to be dealing with aerosol/airborne transmission of the coronavirus?

By
68

For months now, virologists and epidemiologists have been debating a simple question about COVID-19 transmission: How small does a particle exhaled by an infected person have to be before it’s too small to spread the virus? We know that ballistic droplets, the comparatively large globules expelled when breathing, speaking or singing that fall to the ground quickly, generally don’t travel farther than six feet, and are the basis of virus-fighting guidelines like social distancing and masking. But some scientists have argued for months that there’s evidence to suggest the virus that causes COVID can also hitch a ride on droplets small and light enough to hang in the air for hours, and that these “aerosols,” as they are called, might be a substantial contributor to the spread of the pandemic.

Back in July, the World Health Organization acknowledged that aerosols might play a role in spreading COVID: “We have to be open to this evidence and understand its implications regarding the modes of transmission.” Then, this past weekend, the CDC went even further. In a change to their online primer for how the coronavirus spreads, they described COVID-19 as an “airborne disease”—in other words, a disease transmitted primarily through aerosols.

“There is growing evidence that droplets and airborne particles can remain suspended in the air and be breathed in by others, and travel distances beyond 6 feet (for example, during choir practice, in restaurants, or in fitness classes),” the updated language read. “In general, indoor environments without good ventilation increase this risk.”

Soon after the change was released, however, the CDC abruptly changed tack, claiming the update had been posted in error. “Unfortunately an early draft of a revision went up without any technical review,” Jay Butler, the CDC’s deputy director for infectious disease, told reporters Monday.

What gives here? Simply saying ‘the CDC accidentally goofed and shared inaccurate information’ doesn’t do the story justice. Set aside the question of what breakdown in CDC processes led to it being posted prematurely online—someone at the CDC had to write that guidance. If it was wrong, why write it? If it was right, why back away from it?

Unpacking this requires us to take a step back. The first question isn’t “How did the CDC get itself in this messaging mess?” Rather, it’s “why hasn’t the CDC had anything to say about aerosol transmission before?” The central thesis of the now-retracted change in guidance, that “growing evidence” supports an aerosol transmission pathway for COVID-19, has been known for months. It’s the preeminent explanatory model for well-documented, otherwise inexplicable phenomena like COVID superspreader events and the virus being far more contagious indoors than out.

What’s particularly interesting is that the CDC and other federal public health authorities have previously acknowledged this likelihood of aerosol transmission of COVID—just not in such explicit terms. CDC guidance for minimizing the threat of COVID transmission at reopening businesses includes instructions to “consider taking steps to improve ventilation in the building” and to “improve central air filtration”—precautions that do absolutely nothing to inhibit ballistic spread, but are best practices for combatting aerosol transmission. Similarly, EPA guidelines on indoor air and coronavirus state that “when used along with other best practices … increasing ventilation can be part of a plan to protect yourself and your family.”

How, then, to explain the CDC’s reluctance to come right out and acknowledge that we appear to be dealing with aerosol/airborne transmission of the coronavirus?

One clue might be found in the EPA guidance mentioned above. Three separate EPA fact sheets mention air filtration and ventilation as tools to help inhibit the spread of COVID-19, and all three contain a version of the same caveat: “By itself, increasing ventilation is not enough to protect people from exposure to the virus that causes COVID-19.” Anti-aerosol measures, the government maintains, should only be taken in addition to the ordinary steps (masking, distancing, and the like) that are otherwise recommended to stop the spread of the coronavirus.

This framing highlights one of the biggest difficulties remaining in our understanding of COVID transmission: While it looks increasingly clear that both ballistic and aerosol transmission is taking place, we don’t know what proportion of cases are attributable to each. And what helps protect against the one isn’t the same as what protects against the other.

“There are implications—pretty significant ones—related to mask-wearing, for instance,” Dr. Jeff Niederdeppe, a Cornell professor of communication who teaches strategic health messaging, told The Dispatch. “What has kind of been the message that this is the best we can do, is wear masks—well, if aerosol transmission is responsible for a huge proportion of the cases, that directly undermines that kind of guidance.”

You can easily imagine a scenario, then, where the CDC is loath to explicitly describe COVID-19 as an “airborne disease” on the grounds that such language—even if true—might mislead people into thinking the anti-virus precautions to which we’ve become accustomed aren’t any use after all.

Of course, there’s also always the specter of outside interference to consider. The Trump administration has not exactly covered itself in glory when it comes to managing public health narratives during the pandemic, and in recent weeks has on several occasions been caught pressuring its public health experts to change health guidance to better fit their political aims.

Photograph by Image Point FR-LPN/BSIP/Universal Images Group/Getty Images.

68
By
Comments (68)
Join The Dispatch to participate in the comments.
 
  1. Midge

    Droplet size obviously exists on a continuum from ballistic gobs to tiny aerosols. Protocols, on the other hand, tend to be discrete. Not just discrete, but also few in number, so it's feasible for all medical personnel to recall them as needed. And the word I've heard is that medical protocol so far just hasn't had a good category for SPATs.

    Classic airborne transmission (CAT for short) is like measles: the aerosols are *very* tiny and *very* infectious. (Diseases like measles might even lower the viscosity of people's secretions to increase the fineness of aerosols produced.) There's a familiar protocol for managing CATs (unlike actual felines, who reject management). And then there's a familiar protocol for managing diseases spread by ballistic droplets. What there hasn't been, apparently, is a familiar widespread protocol for managing a SPAT (small airborne particle transmission), a form of transmission between large droplet transmission and CAT. Up till now, the protocol for "airborne transmission" has been CAT protocol, "treat it like measles" (that is, like measles in an unvaccinated population), but that would be overkill for a SPAT like Covid-19. Quoting someone who should know:

    "It’s important to distinguish SPAT from 'classic airborne transmission' (let’s call it CAT). The CAT pathogens (TB, measles, VZV) have very different transmission dynamics than SPAT pathogens, as I outlined here (R0s of >10, household transmission rates of 50-90%). The distinction is important because for most healthcare epidemiologists, using the term 'airborne' implies a common set of 'one-size fits all' interventions to prevent transmission, interventions that require resource-intensive engineering controls and PPE requirements. It is not at all clear that such interventions are required to prevent transmission of SPAT pathogens. In fact, most evidence (and real world experience) suggests that they are not. This is why the droplet-airborne dichotomy has served us fairly well over the years—either because droplet precautions appear to be pretty effective at preventing SPAT, or because SPAT is rare even among those viruses capable of it."

    https://haicontroversies.blogspot.com/2020/07/a-tiresome-spat.html

    The smallest physical units might be quantized (hence quantum physics) but macro-reality effectively happens on a continuum. Lived reality is both continuous and non-narrative. But the minds we use to perceive it latch onto narratives and categories. This is true even of minds trained for STEM fields, and what is a protocol but a story to follow for handling a particular category of scenario? A center for disease control may do plenty of research, but its first duty is to have good protocol to, well, *control* disease, including dissemination of easy-to-follow protocol for the mass public. Lacking a well-worn protocol for SPATs, the human mind has been trained to respond to "airborne" with CAT protocol, to mentally categorize all airborne transmission as CAT. And no denial of Covid-19's impact is necessary to see that mentally categorizing it as a CAT when it's not would needlessly spread fear and drain resources.

    Collapse
  2. Deleted Comment

    This comment has been deleted

  3. Avatar photo
    Adam

    Excellent COVID work as usual Andrew!

    Collapse
  4. Avatar photo
    Logical

    For the sake of the country, please listen to me one time.

    The evidence of aerosolized transmission was no clear in Feb/March time frame, though suspected.

    That's why, Fauci, the Surgeon General, and others discouraged the use of masks for PRESERVING LIMITED SUPPLIES FOR THE HEALTH WORKERS.

    We subsequently understood that aerosolized transmission is the predominant mode.

    THEREFORE, anything on your face TRAPS the aerosols thus preventing outright or reducing substantially the chance of YOUR infection from transmitting.

    I am not not an epidemiologist but I have a Ph.D. in materials; in case you ask who the F are you. I have significant training in small particle diffusion mechanisms.

    Please wear a mask.

    Collapse
    1. Mary Stine

      Thank you sir, good to hear from an expert in materials.

      Collapse
    2. 2357958

      Health care workers were never going to wear cloth masks. Why did Fauci not tell the public to wear cloth masks?

      I know we've collectively memoryholed pre-2020 mask science, but Fauci was telling the truth when he said masks don't work. That was the prevailing consensus over decades about masks.

      Prove me wrong. Show studies and/or recommendations for masks from pre-2020. There's plenty of studies and recommendations. They just all happened to be anti-mask (excepting medical/N95 masks in healthcare settings). The only ones pro-mask mysteriously showed up post-covid.

      Collapse
      1. Avatar photo
        Logical

        Who is talking about cloth masks for healthcare workers?
        Good luck with your theories.

        Collapse
        1. 2357958

          You said that Fauci discouraged mask use to protect the supply for healthcare workers. If Fauci was really doing that, why didn't he recommend cloth masks to the public? My entire point is that healthcare workers were never going to wear those (and they're usually homemade anyway). How would encouraging cloth masks threaten supplies for healthcare workers?

          The explanation offered for Fauci doesn't add up.

          Collapse
  5. Scott N.

    Re: masks, I think one problem is the fact that this is a fundamentally different virus situation than say, Ebola, where 1 particle has a high likelihood of killing you, so ANY breach is likely to be lethal. Richard Preston's excellent but chilling accounts tell this tale. With COVID, it's about the viral load, so it's how most people, even most vulnerable elderly will survive and may even be mostly asymptomatic, but even a young & no-conditions nurse or doctor can be struck down.

    Where the messaging has also been poor is that there's a middle ground between N95 and most cloth masks - nonwoven surgical masks (even those marked as "non-medical" or "general purpose", which tests show block a lot more viral particles.* Moreover, there are various mask braces that can be made or purchased^ that seal up the sides to make a surgical mask a near-95 or at least drastically better than a cloth or loose-fitting one. The biggest problem with disposable surgicals of course, is the waste/landfill problem; however, that's a separate issue. The other upside is that they're a lot more breathable than most cloth ones.

    Masks don't even need to be that effective to blunt a curve, since an exponential outbreak works in both directions, where small decreases in the transmission plays an outsized role both in terms of outright spread and in terms of case severity for those who do get it.

    The security theater with COVID hasn't been the masks, but instead much more the surface cleaner shortage. Relentless surface cleaning isn't as important as ventilation, and that does seem clear now.

    I also quite agree it was bad on Fauci and the SG to not wear masks early.

    * https://olv.duke.edu/news/researchers-created-a-test-to-determine-which-masks-are-the-least-effective/ - Duke study on mask types & https://medium.com/@fixthemask/why-are-melt-blown-fabric-masks-better-than-cloth-masks-cf7975bc7edf

    ^ https://www.fixthemask.com and https://www.bellus3d.com/solutions/mask-fitter are two examples

    Collapse
  6. Joe1776

    I think that many experts don't know the answers and they are trying to be careful. The important thing is that people are getting logical advice as we find out more and have been for the most part since the beginning. Wear a mask inside when in public spaces and outside when you can't socially distance. Outdoors is safer then indoors. Elderly people and those with certain pre existing conditions are most at risk etc.

    The big exception was when Fauci and the Surgeon General were telling us not to wear masks early on. Fauci explained that he lied because they did not want medical staff to run short. Other than that the behaviors the experts endorsed have been fine and about as widely known as can be expected.


    Collapse
  7. Avatar photo
    Tracie

    "We know that ballistic droplets, the comparatively large globules expelled when breathing, speaking or singing that fall to the ground quickly, generally don’t travel farther than six feet, and are the basis of virus-fighting guidelines like social distancing and masking. But some scientists have argued for months that there’s evidence to suggest the virus that causes COVID can also hitch a ride on droplets small and light enough to hang in the air for hours, and that these “aerosols,” as they are called, might be a substantial contributor to the spread of the pandemic."
    ______________________________________

    Really appreciate the distinction b/t droplets and airborne particles laid out from the first paragraph of this article. If we're going to have these words thrown around, it's really important to understand what they mean.

    However, if it gets definitively declared airborne, most people with children in school can expect to have them home the rest of the year.

    Collapse
  8. Pearse

    It sounds like a classic case of anointed experts not trusting the benighted plebes.

    Collapse
  9. Jess

    Aerosols are simply particles smaller than 5 micrometers. Particles bigger than that are typically called droplets. We know the virus is transmitted in particles emitted by contagious people. The question is: What size particles cause the most transmission? Naturally, this is very difficult to study. You can’t randomly assign thousands of people to be sprayed with either the virus or a placebo in different sized particles.

    Besides, in reality, there is no clear dichotomy between large droplets and small aerosols. There is a continuous spectrum of particle sizes, and other important factors must be considered, such as the volume and speed of exhalation.

    Does the answer to this question of particle size really matter as far as recommended public health measures?

    We know that gathering outdoors is far safer than indoors, and that good ventilation is important if you have to be indoors. I don’t see how particle size calls that into question. As far as mask wearing, any mask than can block any sized particles is better than nothing. In fact, there is a hypothesis that even if a mask doesn’t block all particles, the wearer receives a lower dose of particles which can lead to milder disease.

    As far as distance, some infection may happen indoors at a distance further than 6 feet, but close contact still appears to be the dominant means of spread. Should we make the distance recommendation larger? That might be the most conservative measure, but schools are already struggling to maintain the six feet.

    I think the CDC statements on aerosols would have the most effect in health care settings. If aerosols are a big means of transmission than everyone needs an N95 (still in scare supply), and all Covid patients must be isolated in negative pressure rooms. As far as public health for citizens, I would prefer that the CDC stick to concrete and consistent recommendations, and stay away from the nebulous questions of particle size

    Collapse
    1. Deleted Comment

      This comment has been deleted

    2. Avatar photo
      Carl M

      Very thoughtful and well-informed comment.

      Collapse
  10. Mike M

    I'm glad you stay on this story, because in the years to come learning from what is happening here can help us do a better job in the future. Watching this bungling in real-time has been disheartening.
    My best guess as to what happened here is 1) That there is more good evidence of some transmission from virus containing aerosol drops. 2) The report was released before they decided what do with that information, and what practical recommendations they could make to an exhausted public.
    Messaging fatigue has set in. I really think the public not really much interested in additional guidance about what to do with respect to COVID. It get the sense that we have just decided to power through with what we are doing now. In that light, how much difference do you think warning us that the already invisible droplets are even smaller would make? Hospitals might take note and step up air filtration, but they would be fools not to have already done so. I think the level of masking, distancing and limits to social gatherings have maxed out. It's vaccine or bust. Personally. I'm grateful to live in a time where vaccine is at least an option.

    Collapse
Load More