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Published on National Health and Medical Research Council (https://www.nhmrc.gov.au) Generated on 12 May 2017 @ 10:15am A1.1.1 Routes of transmission Contact transmission Contact is the most common mode of transmission, and usually involves transmission by touch or via contact with blood or body substances. Contact may be direct or indirect. Direct transmission occurs when infectious agents are transferred from one person to another — for example, a patient’s blood entering a healthcare worker’s body through an unprotected cut in the skin. Indirect transmission involves the transfer of an infectious agent through a contaminated intermediate object or person — for example, a healthcare worker’s hands transmitting infectious agents after touching an infected body site on one patient and not performing hand hygiene before touching another patient, or a healthcare worker coming into contact with fomites (e.g. bedding) or faeces and then with a patient. Examples of infectious agents transmitted by contact include multi-resistant organisms (MROs), Clostridium difficile, norovirus and highly contagious skin infections/infestations (e.g. impetigo, scabies). Droplet transmission Droplet transmission can occur when an infected person coughs, sneezes or talks, and during certain procedures. Droplets are infectious particles larger than 5 microns in size.6 Respiratory droplets transmit infection when they travel directly from the respiratory tract of the infected person to susceptible mucosal surfaces (nasal, conjunctivae or oral) of another person, generally over short distances. Droplet distribution is limited by the force of expulsion and gravity and is usually at least 1 metre. However, droplets can also be transmitted indirectly to mucosal surfaces (e.g. via hands). Examples of infectious agents that are transmitted via droplets include influenza virus and meningococcus. Airborne transmission Airborne dissemination may occur via particles containing infectious agents that remain infective over time and distance. Small-particle aerosols are created during breathing, talking, coughing or sneezing and secondarily by evaporation of larger droplets in conditions of low humidity. Certain procedures, particularly those that induce coughing, can promote airborne transmission. These include diagnostic sputum induction, bronchoscopy, airway suctioning, endotracheal intubation, positive pressure ventilation via face mask and high-frequency oscillatory ventilation. Aerosols containing infectious agents can be dispersed over long distances by air currents (e.g. ventilation or air conditioning systems) and inhaled by susceptible individuals who have not had any contact with the infectious person. These small particles can transmit infection into small airways of the respiratory tract. Examples of infectious agents that are transmitted via the airborne route include measles (rubeola) virus, chickenpox (varicella) virus and M. tuberculosis. Other modes of transmission Transmission of infection can also occur via common sources such as contaminated food, water, medications, devices or equipment. Footnotes: 6. Siegel JD, Rhinehart E, Jackson M et al (Health Care Infection Control Practices Advisory Committee) (2007) Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings, June 2007. United States Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dhqp/pdf/isolation2007.pdf. '1' Source URL (modified on 05/10/2010 - 08:59): https://www.nhmrc.gov.au/book/australian-guidelines-prevention-and-control-infectionhealthcare-2010/a1-1-1-routes-transmissi '2'