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Session 1: Introducing human infectious diseases

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This figure comprises simple flow diagrams which summarises the routes of indirect person-to-person transmission. Part (a) shows airborne infections being transmitted from one person to another in the water droplets that are expelled in a cough or sneeze; this is also a route of transmission of infectious agents to non-living objects in the environment (e.g. a cup or spoon) These infection-carrying objects, referred to as fomites, can then transmit it orally to another human who uses that object. Also shown are the routes of transmission of waterborne infections, which can originate through contamination by either fomites or human faeces. Infectious agents present in contaminated water bodies (e.g. rivers, lakes) can be transferred to humans who drink the water (this is the faecal–oral route) and to foods (e.g. in contaminated meat or salad leaves), which are then consumed (the foodborne route). Part (b) shows another route of transmission: blood-borne infections are transferred from one individual to another individual via the transfusion of blood.