Table 3.1The scope and definitions of three transmission models for the systematic review

Mode of transmissionDefinitionExamples of the agents
AirborneTransmission of disease caused by dissemination of droplet nuclei that remain infectious when suspended in air over long distance (>1 m) and time. Airborne transmission can be further categorized into obligate or preferential airborne transmission.
Obligate airborne transmission refers to pathogens that are transmitted only by deposition of droplet nuclei under natural conditions.
Preferential airborne transmission refers to pathogens that can initiate infection by multiple routes, but are predominantly transmitted by droplet nuclei.
Pulmonary tuberculosis, measles, chickenpox
Opportunistic airborneTransmission of droplet nuclei at short range during special circumstances, such as the performance of aerosol-generating procedures associated with pathogen transmission.SARS-Coronavirus, influenza
DropletDroplets are generated from an infected (source) person primarily during coughing, sneezing and talking. Transmission occurs when these droplets, containing microorganisms, are propelled a short distance (usually <1 m).Adenovirus, respiratory syncytial virus, influenza, SARS-Coronavirus

SARS, severe acute respiratory syndrome.

From: 3, Infection and ventilation

Cover of Natural Ventilation for Infection Control in Health-Care Settings
Natural Ventilation for Infection Control in Health-Care Settings.
Atkinson J, Chartier Y, Pessoa-Silva CL, et al., editors.
Copyright © 2009, World Health Organization.

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