Table 2.

Modes of infection transmission

Mode of transmission	Description	Example pathogensa
Contact	• Infectious organisms transferred from an infected person to a susceptible individual through direct physical contact, or indirectly via contaminated objects • Susceptible individual can self-inoculate by touching own eyes/nose/mouth with contaminated hands	• Varicella-zoster virus • Norovirus • Respiratory syncytial virus • Methicillin-resistant S. aureus (MRSA) • C. difficile • SARS-CoV-2
Droplet	• Larger infectious particles (>5 μm) generated by coughing or sneezing travel 3–6 ft from the infected individual to the mucosal surfaces of the susceptible person (conjunctivae and nasal/oral mucosa)	• Adenovirus • Influenza virus • Rhinovirus • M. pneumoniae • SARS-CoV-2
Airborne (aerosol)	• Infected person generates smaller infectious particles, or aerosols (<5 μm) through coughing, sneezing, talking, exhalation and aerosol-generating procedures • Particles are suspended in air for longer periods of time than larger droplets, and therefore reach susceptible individuals through greater distances and time	• Measles virus • M. tuberculosis • Varicella-zoster virus • Influenza virus (probable) • Aspergillus • SARS-CoV-2

^aNote that our current understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) suggests that the virus might transmit through all of these modes