Short-range airborne transmission of expiratory droplets between two people

Li Liu, Yuguo Li, Peter Vilhelm Nielsen, Jianjian Wei, Rasmus Lund Jensen

Research output: Contribution to journalJournal articleResearchpeer-review

48 Citations (Scopus)


The occurrence of close proximity infection for many respiratory diseases is often cited as evidence of large droplet and/or close contact transmission. We explored interpersonal exposure of exhaled droplets and droplet nuclei of two standing thermal manikins as affected by distance, humidity, ventilation, and breathing mode. Under the specific set of conditions studied, we found a substantial increase in airborne exposure to droplet nuclei exhaled by the source manikin when a susceptible manikin is within about 1.5 m of the source manikin, referred to as the proximity effect. The threshold distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route. The short-range modes include both the conventional large droplet route and the newly defined short-range airborne transmission. We thus reveal that transmission occurring in close proximity to the source patient includes both droplet-borne (large droplet) and short-range airborne routes, in addition to the direct deposition of large droplets on other body surfaces. The mechanisms of the droplet-borne and short-range airborne routes are different; their effective control methods also differ. Neither the current droplet precautions nor dilution ventilation prevents short-range airborne transmission, so new control methods are needed.
Original languageEnglish
JournalIndoor Air Online
Issue number2
Pages (from-to)452-462
Publication statusPublished - 2017


  • Building ventilation
  • Interpersonal exposure
  • Large droplet transmission
  • Respiratory infection
  • Short-range airborne route

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