interessante punto di vista, diciamo che generalmente il dibattito verte sulla dimensione per capire droplet/aereosol e sul tempo di evaporazione. Resta il fatto che la respirazione produce aerosol con tutto quello che ne consegue logicamente.
Table adapted from Morawska 2006, with similar numbers reported in the Fiegel 2006 review:
ACTIVITY | NUMBER OF DROPLETS PRODUCED | SMALL (1-2 ΜM) AEROSOLS? |
---|
Normal breathing (5 min) | A few | Some |
Single strong nasal exhalation | Few to a few hundred | Some |
Counting out loud (talking) | Few dozen to few hundred. Some sources say a few thousand (Xie 2007) | Mostly |
Cough | Few hundred to many thousand | Mostly |
Sneeze | Few hundred thousand to a few million | Mostly |
If you want a more specific breakdown, you can look at table 2 from Nicas 2005, but these numbers are estimates, and you will see different numbers even in this same paper:
Older studies concluded that humans primarily produce large droplets, but they were significantly limited because their instruments were insensitive to smaller sizes. (Morawska 2006) Recent research has indicated that as many as 80-90% of the particles generated by human exhalation are smaller than 1 µm in size. (Papineni 1997) Although the exact size of droplets produced is still debated, most sources agree that speaking, coughing, and sneezing produce droplets that are sufficiently small to remain airborne. (Fiegel 2006; Chen 2010)
Interestingly,
the total amount of bioaerosols produced varies tremendously among individuals, with some people creating very few, and others acting as “super producers”. (Fiegel 2006)
I wonder whether this explains why we have observed super-spreaders of SARS and COVID-19, as “it appears that a minor percentage of the population will be responsible for disseminating the majority of exhaled bioaerosol”. (Fiegel 2006)
Super producers: Figure 2 from Fiegel 2006
However,
whether these aerosols are capable of transmitting disease still depends heavily on the number produced, the concentration of the infectious agent, the virulence of the microbe, environmental factors (the virus needs to be able to survive, whether in the air or on a surface, until it enters a host), and the health and immunity of the host. (Morawska 2006) Although it is clear that aerosols are commonly produced, it is also clear that the vast majority of disease transmission occurs among people who are in very close contact and therefore exposed to the largest of the droplets.
The fact that humans constantly produce aerosols is really important when assessing studies of aerosol generating procedures. The result sections of these papers will often only present a change in aerosols from baseline, and frequently our procedures won’t produce more droplets. However, if you look closely, we are already producing a ton of aerosols, and even if the procedures don’t produce more, their ability to spread those aerosols further is a big concern. (Simmonds 2010; Rule 2018)