• Primary routes of infectious disease transmission are direct and indirect contact, droplet, and airborne.

The primary routes of infectious disease transmission in U.S. workplace settings are contact, droplet, and airborne. Contact transmission can be sub-divided into direct and indirect contact. Direct contact transmission involves the transfer of infectious agents to a susceptible individual through physical contact with an infected individual (e.g., direct skin-to-skin contact). Indirect contact transmission occurs when infectious agents are transferred to a susceptible individual when the individual makes physical contact with contaminated items and surfaces (e.g., doorknobs, patient-care instruments or equipment, bed rails, examination tables). Two examples of contact transmissible infectious agents include Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant enterococcus (VRE).

Droplets containing infectious agents are generated when an infected person coughs, sneezes, or talks, or during certain medical procedures, such as suctioning or endotracheal intubation. Transmission occurs when droplets generated in this way come into direct contact with the mucosal surfaces of the eyes, nose, or mouth of a susceptible individual. Droplets are too large to be airborne for long periods of time, and droplet transmission does not occur through the air over long distances. Two examples of droplet transmissible infectious agents are the influenza virus which causes the seasonal flu and Bordetella pertussis which causes pertussis (whooping cough).

Airborne transmission occurs through very small particles or droplet nuclei that contain infectious agents and can remain suspended in the air for extended periods of time. When these particles are inhaled by a susceptible individual, they enter the respiratory tract and can cause infection. Since air currents can disperse these particles or droplet nuclei over long distances, airborne transmission does not require face-to-face contact with an infected individual. Airborne transmission only occurs with infectious agents that are capable of surviving and retaining infectivity for relatively long periods of time in airborne particles or droplet nuclei. Only a limited number of diseases are transmissible via the airborne route. Two examples of agents that can be spread through the airborne route include Mycobacterium tuberculosis which causes tuberculosis (TB) and the measles virus (Measles morbillivirus), which causes measles (sometimes called “rubeola,” among other names).