While there are many ways of spreading COVID-19, the best medical analysis currently is that the virus is transmitted via airborne events from aerosols. (That's a fancy term for breathing.) Perhaps, to stay safe, we might strategically avoid moments that produce the most aerosols.
The generation of aerosols from patients with COVID-19 has long been a concern in healthcare. After all, many of the procedures especially placing and removing breathing tubes (intubation and extubation) from these patients, are up-close and personal, although certainly not lasting the 15 minutes necessary to be considered direct contact. Nevertheless, in the absence of any, let alone good evidence, physicians and respiratory therapists, among others, suited up "full Hazmat" in these situations.
With time, it became clear that those moments were not producing breathes with large amounts of viral particles and fluids, at least to the degree feared. I reviewed a study that showed these results a month or so ago. This latest opinion piece summarizes what we know about our breaths and the contents, other than air, that we spew forth. Physiologically, our breath can be fast or slow, deep or shallow – depending upon the combination, the exhaled breath can travel far and wide or near and narrow. The physics of airborne particles relies on how fast they move, how large there are, in both size and weight, and gravity – all variables we have used for over a century in determining the trajectory of projectiles coming from cannons and missile silos
What factors determine the transmission risk?
- Force of the breath, the more forceful, the larger the size of the exhalation cloud. That is why coughing, singing, and yelling are more concerning.
- Distance, even the largest exhalation cloud, extends only so far. The closer you are to another's exhalation, the greater quantity of their breath you might inhale
- Duration, the longer you remain in the exhalation cloud of another, the greater the possibility of transmission
- Viral particles The first three are physical traits we can recognize, how deeply another is breathing, how close we are to them, and for how long. But the amount of viral particles present in the breath of another is unknown to us; our current understanding of the temporal highs and lows are a bit fuzzy. The best we might say is that the number of viral particles begins to rise a day or so before symptoms and abates 3 to 4 days later during recovery. But that doesn't cover the asymptomatic and those not doing so well, and in any case, would require a Magic Eight Ball way of knowing that someone was going to become symptomatic in a day or so.
To these four, we should add that the surrounding environment may also enhance or mitigate transmission. A crowded room or poorly ventilated space doesn't allow as much dispersion of particles and distance as the great out of doors. Parenthetically, that is why the igloos of various shapes and sizes popping up to provide outdoor dining are more likely pandemic theater than helpful.
The authors conclude that it is not the specific procedure in healthcare that is problematic, but the context, those four forces. That is the lesson. Masks reduce the force and distance of exhalations by merely providing a cloth/paper barrier. Social distancing reduces distance and duration. We cannot control the viral particle variable other than carefully selecting the members of our pandemic pod or posse. With the holidays coming, that is not such an easy option to navigate.
I mention this paper not because of its new insights but because it represents first-responders' thoughts - the canaries in the COVID-19 mine. They have no political agenda or conspiracy to control, they simply want to survive, and these are the tools they have found useful. If you want to thank them for their service, then perhaps it is time to do as they do and as they ask.
Source: What are aerosol generating procedures? JAMA Surgery DOI: 10.1001/jamasurg.2020.6643