Table 1: Droplet versus airborne transmission: implications for public health and healthcare worker protection
1a. Droplet transmission 1b. Airborne transmission
If an infectious pathogen spreads predominantly through large respiratory droplets that fall quickly, the most important public health measures are: respiratory hygiene (e.g. sneezing into tissues) disinfecting surfaces and objects (fomites) onto which droplets may have fallen reducing direct contact (e.g. do not shake hands with others or touch one’s own face) staying physically apart from others at a distance that reflects the effect of gravity on droplets (1-2 metres) wearing facemasks within that droplet distance physical barriers (such as visors of plastic screens) providing respirator-grade protection for healthcare staff who undertake so-called “aerosol-generating” procedures. These contact, droplet and fomite precautions do not distinguish between indoor and outdoor settings, since a gravity-driven mechanism for transmission would operate similarly in both. If an infectious pathogen is mainly airborne, a person could potentially be infected when they inhale aerosols emitted in the breath of an infected person. These aerosols may remain suspended in the air for many hours. Reducing airborne transmission requires measures to avoid inhalation of infectious aerosols, including engineering controls in indoor spaces (ventilation, air filtration) reducing crowding (e.g. by encouraging people to work from home if possible) reducing time spent indoors (e.g. frequent breaks for school classes) maximising physical distance between people indoors (even beyond 2 metres) wearing masks whenever indoors careful attention to mask quality (to maximise filtration) and fit (to avoid air getting in via gaps) taking particular care in indoor activities that generate aerosols (e.g. speaking, singing, exercising) providing respirator-grade protection for health-care staff and other front-line workers