2.1.2 Indirect transmission of pathogens

Indirect transmission occurs when an infected person sheds bacteria into the air, water, food or onto other objects in the environment (known collectively as fomites), which can then infect someone else. Figure 4 summarises these indirect transmission routes.

Figure 4 Routes of indirect person-to-person transmission of infection.

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This figure comprises simple flow diagrams which summarises the routes of indirect person-to-person transmission. It 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).

Figure 4 Routes of indirect person-to-person transmission of infection.

Fomites are objects in the environment, such as door handles, cups and pens, that are routinely touched and can transmit infections. Healthcare-associated infections (HCAIs) can easily be indirectly transmitted to susceptible patients via fomites. A quarter of HCAIs are caused by antibiotic-resistant bacteria such as MRSA.

In the next activity, you will look at fomites that might transmit HCAIs.

Activity 2 Fomites and healthcare-associated infections

Timing: Allow about 5 minutes

Identify the fomites in this picture of hospital staff in 2001 that might transmit HCAIs.

Figure 5 Hospital staff photographed in 2001.

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The photo shows a nurse talking to a group of three young doctors. Her arms are bare from the elbow and she is wearing a wristwatch. All three of the doctors have a stethoscope around their neck and a staff badge just below waist height. The two male doctors are both wearing long-sleeved shirts with long ties that are not tucked into their trousers, and the female doctor is wearing an unbuttoned long-sleeved cardigan over a loose-fitting blouse.

Figure 5 Hospital staff photographed in 2001.

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Answer

Neck ties, stethoscopes, long-sleeved clothing, hospital badges worn at waist height and wrist watches could all brush against patients with infections and act as fomites, transmitting the infection to a susceptible individual. Consequently, in UK hospitals today, all staff must have their arms bare below the elbows and wrist watches and neck ties are banned.

Sanitation and hygiene both play an important role in preventing indirect transmission via the routes summarised in Figure 5. Next, you will look at how sanitation and hygiene prevent faecal–oral transmission and the effect that this could have on antibiotic use.