Droplet transmission occurs when bacteria or viruses travel on relatively large respiratory droplets that people sneeze, cough, drip, talk, sing, or shout into the air. These droplets usually travel only short distances before settling, most falling out of the air within 3 to 6 feet. These droplets are loaded with infectious particles.
They can be spread directly if people are close enough to each other. Infected droplets can land in the nose, eyes, or mouth and spread infection.
More often, though, fomites are involved. The droplets land on hands, toys, tables, mats, or other surfaces, where they sometimes remain infectious for hours. Hands that come in contact with these surfaces (doorknobs, telephones, pens, etc.) become contagious. Then, when the infectious hand touches the nose, eyes, or mouth, the infection is able to enter the new person.
Many common infections can spread by droplet transmission in at least some cases, including: Adenovirus, COVID-19, Common cold, Diphtheria, Fifth disease, Influenza, Meningitis, Mycoplasma, Mumps, Pertussis (whooping cough), Plague, RSV, Rubella, Strep (strep throat, scarlet fever, pneumonia).
Masks have been shown to reduce droplet transmission, especially if someone needs to be within 6-10 feet of someone contagious. Having said that, some of these organisms (such as RSV) spread by more than one route, so a mask alone may not be sufficient
Covering the mouth or nose when coughing or sneezing decreases droplet spread—and can make hand cleansing even more important, unless people learn to cough into their elbow.
Frequent hand cleansing, especially with instant hand sanitizers, can help prevent droplet transmission. Hand cleansing is most important before eating and before touching the nose or eyes.
Cleaning or disinfecting commonly touched infected surfaces (doorknobs, faucet handles, shared toys, mats in daycare) can also help. Wearing a mask may help for brief, short exposures.
Jayaweera M, Perera H, Gunawardana B, Manatunge J. Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy. Environ Res. 2020;188:109819. doi:10.1016/j.envres.2020.109819
United States Center for Disease Control and Prevention. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings (last updated May 2022) https://www.cdc.gov/infectioncontrol/pdf/guidelines/isolation-guidelines-H.pdf