Transmission-based precautions are intended for patients with highly transmissible pathogens for which additional precautions are needed. Airborne transmission is by small-particle residue of evaporated droplets containing microorganisms that remain suspended in the air for long periods of time or dust particles containing the infectious agent. Microorganisms transmitted in this manner can be disbursed by air currents and may be inhaled by susceptible hosts. Special air handling and ventilation are required to prevent airborne transmission. Microorganisms that are transmitted by the airborne method include Mycobacterium tuberculosis, rubeola viruses, and varicella viruses.
Droplet transmission has a specific mechanism of transfer, and droplets are five microns or larger.
Droplets are generated from the infected source, usually from coughing, sneezing, talking, or from procedures such as a bronchoscopy or suctioning. Transmission occurs when droplets containing microorganisms from an infected person are propelled a short distance through the air and onto the conjunctiva, nasal mucosa, or mouth of another person. Contact transmission can be from direct or indirect contact between an infected or colonized person and a susceptible host. Patients positive for MRSA who have a productive cough should still be cared for using contact precautions because of the mode of transmission for this microorganism. In addition to standard precautions, contact precautions include the following.