1/ Inhalation dose occurs in both the near field (close contact) and far field in the same indoor space. It is reasonable to assume that near field concentrations in the breathing zone are < 2 to 8 x the far field based on measurements & modeling.
https://twitter.com/zeynep/status/1385707216280375298
2/ The actual magnifier depends on distance, whether and type of masks worn, mixing conditions (TKE) between infector and receptor, mode of emissions (cough vs. speak vs. breath), body orientation of infector & receptor and controls in the far field.
3/ Assuming the magnifier is 4 x, then 15 minutes in close contact with an infector is the same as 60 minutes in the far field. In each case the dose is the same and the probability of infection from those doses should be the same.
4/ Inhalation dose associated w/ close contact (near field) w/ an infector is certainly important if the time in close contact is sufficient. But the far field may also be important and a person could have an additive dose w/ some time in close contact & some time in far field.
5/ What's important is that the aerosol particles are airborne whether in close contact or far field and the two regimes are additive for inhalation dose while in an indoor space.
6/ Reduce inhalation dose in the near field by universal mask wearing and some distancing. Reduce in the far field with universal mask wearing, increased ventilation, improved central filtration, and portable HEPA filtration systems.
7/ Portable HEPA filtration systems may also reduce inhalation dose while in close contact due to their power input (enhanced mixing and dispersion) to indoor air. All of this is to say ... it's airborne & I would not rule out the far field as also being important.
• • •
Missing some Tweet in this thread? You can try to
force a refresh
