Transmission-based precautions (TBPs) definitions literature review update

What is changing in this update?

New research questions

New research questions have been considered as part of this update. These look at:

New search terms

New search terms have been added. The evidence search goes back to include all scientific papers that have been published since the year 2000.

See the NIPCM literature review development process for more information. 

See the full list of questions considered as part of this review and the search terms.

Evidence for mask wearing

Stakeholders requested that this review also considers where and when healthcare workers should wear masks and the type of mask they should wear (surgical mask or respirator). Evidence for mask effectiveness is being considered in separate literature review updates .

Why are transmission descriptors (contact, droplet, airborne) being reviewed?

The pandemic highlighted that the way in which respiratory transmission is currently described (droplet and airborne transmission) may not reflect what is happening in real life. We need to look at whether there is a better way to describe transmission, and whether this would lead to any improvements in infection prevention and control (IPC) practice.

Understanding how infectious agents are released into the air and the risks associated with particle size and distance from source well help inform this. Reviewing the evidence to understand if there is increased risk associated with certain medical procedures will also inform IPC practice.

The World Health Organization (WHO) and Centers for Disease Control (CDC) have also reviewed transmission descriptors indicating a global shift in the way transmission routes are described. ARHAI Scotland were invited to meet with the WHO global IPC unit to discuss the topic and our literature review findings were well received.

Why were transmission descriptors not reviewed during the pandemic?

Work began on reviewing transmission descriptors in 2022 in the third year of the pandemic. The literature review has assessed over 26,000 scientific articles. 61% of all studies included to answer the main research question were published between 2019 and 2022 which reflects the growing interest in this area as the pandemic continued.

What is likely to change in the NIPCM?

The ARHAI Scotland National Policies Guidance and Evidence (NPGE) Working Group are currently developing recommendations for practice. It is likely that ‘droplet transmission’ and ‘airborne transmission’ will be replaced with new definitions to describe respiratory transmission. This will mean changes throughout the NIPCM to update the terminology including the addition of resources to support any guidance changes.

What might this mean for healthcare workers in practice?

It is too early to understand what might change in practice but it is likely that there will be a need for healthcare workers to consider more factors when risk assessing what PPE to wear.

The goal of the NIPCM is to provide healthcare workers in Scotland with guidance that is evidence based, up-to-date, effective, practical, and as a result, safe.  There should be a clear benefit associated with any guidance change and this benefit should outweigh any potential harms. Guidance will only change if these conditions are met.

Supporting resources and education needs will be considered alongside any potential changes to the NIPCM to enable application to practice.

Research questions

  1. What are Transmission Based Precautions (TBPs)?
  2. When should TBPs be applied?
  3. What is the current definition of contact transmission?
  4. What is the current definition of droplet transmission?
  5. What is the current definition of airborne transmission?
  6. How are infectious agents released into the air of the health and care environment from the respiratory tract with consideration of particle size, distance and clearance/fallout time?
  7. Are there reported occurrences of pathogen transmission which do not align with their currently assigned, transmission mode(s)?
  8. Can transmission of infection be described/defined beyond the current categories of contact/droplet and/or airborne?
  9. What factors should be considered when determining whether to discontinue TBPs?
  1.  "transmission based precaution*".mp.
  2.  "additional infection control*".mp.
  3.  "airborne transmission*".mp.
  4.  "droplet transmission*".mp.
  5.  "contact transmission*".mp.
  6.  airborne.mp.
  7.  droplet*.mp.
  8.  "contact precaution*".mp.
  9.  exp Aerosols/
  10.  aerosol*.mp.
  11.  "fomite transmission*".mp.
  12.  Fomites/
  13.  fomite*.mp.
  14.  “additional precaution*”.mp.
  15.  “special precaution*”.mp.
  16.  “enhanced control measure*”.mp.
  17.  bioaerosol*.mp.
  18.  exp Infection Control/
  19.  exp Disease Transmission, Infectious/
  20.  exp infections/ or exp cross infection/ or exp opportunistic infections/
  21. 18 or 19 or 20
  22. ((termin* or end* or cease* or ceasing or stop* or discontinu* or finish*) adj3 ("transmission based precaution*" or "additional infection control*" or "airborne precaution*" or "droplet precaution*" or "contact precaution*" or “additional precaution*” or “special precaution*” or “enhanced control measure*”)).mp.
  23. 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15 or 16 or 17
  24. 21 and 23
  25. 22 or 24
  26. limit 25 to (english language, human studies and yr="2000 - 2023")
  27. Aerosols/
  28. "Respiratory Aerosols and Droplets"/
  29. (aerosol* or bioaerosol* or particle*).mp.
  30. 27 or 28 or 29
  31. ("respiratory tract*" or breath* or speaking or speech or talk* or sneez* or cough* or or AGP or "aerosol generating procedure*" or "medical procedure*" or "dental procedure*" or “surgical procedure*”).mp.
  32. exp Pharmaceutical Preparations/
  33. exp "Nebulizers and Vaporizers"/
  34. (drug* or medicine* or medicinal* or inhaler*).mp.
  35. 30 and 31
  36. 35 not (32 or 33 or 34)
  37. 26 or 36
  38. limit 37 to (english language, human studies and yr="2000 - 2023")