Thread by @CorsIAQ

1/ Inhalation Dose
It's been about inhalation dose from day 1. We have not kept our eye on the ball. Critical pre-vaccination. Critical post-vaccination. Been writing & speaking about this for nearly 20 mos. Reducing inhalation dose is a must. Come on folks, just do it!

2/ Reducing Inhalation dose using layered interventions is still important, whether unvaccinated or vaccinated (breakthrough cases), in close contact (near field) or far field in the same indoor space, in a car or classroom, in a restaurant or apartment, young or old.

3/ Inhalation dose associated with virus laden aerosol particles is defined by the same variables (whether close contact or far field ---- don't bicker about one or the other - I've previously tweeted about this):

Dose(inhal,i) = C(i) x B x t x fdep(i)

4/ For aerosol particles (as opposed to virions in those particles), Dose(inhal,i) is the # of particles in size range i that are inhaled and deposited in the respiratory system. Since infectious viruses are conveyed via these particles, removing particles from air is CRITICAL!

5/ These size fractionated particle numbers can then be converted to size-fractionated particle volume or total volume in different parts of the respiratory system, as we have done with the safeairspaces.com educational tool.

6/ This volume can then be linked to viruses if infectious viral load is known or estimated for different particle sizes, or can be anchored to specific outbreaks with use of a dose-response model (as we did with the model described above).

7/ C(i) is the time-averaged concentration of particles in size range i in the breathing zone of the receptor (#/liter) while in an indoor space.

8/ Importantly, C(i) can be reduced in a number of ways: (a) test and reduce sources of virus-laden aerosol particles in an indoor space, (b) requiring universal mask wearing (to reduce emissions from those infected), (c) wearing a mask, as C(i) is taken as inside the mask.

9/ (d) increasing ventilation (% of supply air that is outdoor air in case of HVAC systems, etc., (e) utilizing or improving filtration; e.g., increase MERV rating of filters in central systems - to MERV13 or better if possible; right-sized standalone HEPA filtration systems.

10/ (f) physical distancing (to reduce the near-field component of inhalation dose), (g) UVGI (upper-room preferred).

11/ Note that UVGI leads to inactivation of viruses in aerosol particles as opposed to removing aerosol particles from the breathing zone, but can be highly effective at reducing the “infectiousness” of aerosol particles.

12/ Reduction of C(i) by (a) to (c) goes a long way to reducing dose in BOTH the near- and far fields. Approaches (d), (e) and (g) can go a long way to further reduce Ci (or infectious viruses associated with C(i) in the case of (g) - UVGI) in the far field.

13/ It is entirely possible to reduce inhalation dose by greater than 95% through the right combination of factors that reduce C(i). None of the steps required are rocket science. So, just do it!

14/ Recall:

Dose(i) = C(i) x B x t x f(i)

B is the respiratory minute volume (volume of air taken in with each breath) and has units of liters/min. This has been an important but overlooked variable throughout the pandemic.

15/ Think working out in a gym, children coming back to the classroom after a lot of running and playing at recess, singing in a choir (deep breaths, etc), serving meals in a busy restaurant, salsa dancing, etc.

16/ Values of B can vary by as much as a factor of 5 to 10 (sometimes even more!) (resting couch potato vs. someone engaged in extremely intense aerobic exercise). In addition, an infected person with increased B also emits more aerosol particles (potentially A LOT more).

17/ The term t is simply time spent in a space challenged by virus-laden particles. It is also an important factor and (teaser) there is NOTHING magical about 15 minutes. It is inhalation dose that matters! Just understand it!

18/ The term fdep(i) is the fraction of particles in size range i that deposit in the respiratory system and takes on values of less than or equal to 1. The location of where these particles deposit in the respiratory system is relevant.

19/ An example deposition curve is shown here for nose breathers engaged in light exercise. Note that for 1 micron particles, approximately 50% are deposited in the respiratory system and 50% are simply exhaled.

20/ Whether you breathe through your nose or mouth does have an effect on how many aerosol particles of a given size deposit in your upper or lower respiratory systems. Example plot here for deposition in alveolar region (deep lung).

21/ Our simulations show that for nose breathers the large majority (approximately 70 to 75%) of aerosol particles and particle volume for those particles of relevance to conveyance of SARS-CoV-2 are deposited in the nose and nasopharynx region.

22/ Appreciable (average around 20 to 25%) occurs in the alveolar region. Deposition in the tracheobronchial region is generally less than 10%, but that does not make this region insignificant by any means.

23/ I want to underscore that inhalation dose occurs in both the near field (close contact) and far field. In fact, it is highly conceivable that someone who is challenged with inhalation of virus-laden particles received some in close contact & some in the far field.

24/ Job 1. GET VACCINATED if you are eligible to do so. Job 2. REDUCE INHALATION DOSE. Reduce C(i) by reducing sources (test), wearing a mask and requiring universal mask wearing in communal indoor spaces,increase ventilation, improve central filtration

25/ Consider portable HEPA filtration (or Corsi-Rosenthal boxes), & consider use of upper-room UVGI if possible. These become highly valuable in situations w/ ventilation constraints. Reduce time in spaces w/ others if you or they have increased breathing rates.... Just do it!