Research finds that particle size is the most important determinant of aerosol behavior.
Many existing recommendations have been based on older studies, however over the last 20 years numerous investigators have directly measured the particle size of infectious aerosols emitted from coughing and exhaled breath.
This is had led to several concrete conclusions pertaining to airborne infection control summarized by Dr. Kevin Fennelly of The Lancet.
- Humans produce a wide range of infectious particle sizes, but pathogens predominate in small particles sizes of <5um which are easily respirable.
- Accumulating data suggests that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted by both small and large particle aerosols.
- These data suggest that health-care workers should be protected from these potentially infectious aerosols when working in close proximity to patients.
- Some surgical masks might offer respiratory protection compared with not wearing a mask. Filtering face piece respirators offer more respiratory protection than surgical masks, and powered air purifying respirator (PAPRs) hoods offer the best protection for most health-care settings.
- Face shields can help decrease exposures to and contamination from large particle aerosols, but they do not offer inhalation protection against small particle aerosols.
- PAPRs have built-in eye protection. Surgical masks and other respirators require a face shield or goggles to protect the eyes to prevent infection.
- Masking of patients can help to partly reduce infectious aerosol exposures to health-care workers, but are not a substitute for physical distancing and other infection control measures.
- Aerosolization of respiratory pathogens is highly variable, at least partly due to the log-normal distribution of infectious aerosols, consistent with so-called super-spreading.
- Airborne infection isolation rooms and other infection control measures against airborne infection are indicated for virulent respiratory pathogens such as SARS-CoV-2.
The core research can be reviewed here.