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Table 3.3 Links in the chain of infection

Modes of transmission

The mode of transmission is the method by which an infectious agent passes from one person or place to another. Considering the mode of transmission allows you to implement the measures required to prevent it.

Direct contact

This is person-to-person spread of infectious agents through physical contact between people. It occurs through normal nursing activities and can happen during aseptic procedures if technique is poor. It can be prevented through good hand hygiene and the use of barriers such as aprons and gloves.

Indirect contact

This occurs when someone comes into contact with a contaminated object. Many items in the healthcare environment can become contaminated, but the most likely routes of spread are inadequately decontaminated items of equipment used for diagnosis or treatment. Transmission is prevented by effective cleaning and decontamination and good hand hygiene.

Droplet transmission

When people cough, sneeze or even talk, they expel droplets of respiratory secretions and saliva. These droplets will travel about a metre from the person expelling them, and may contain the agents responsible for respiratory infections such as influenza or tuberculosis. Transmission is prevented through isolating the affected patient and using masks, aprons and gloves to provide a barrier, and also through good hand hygiene as there will almost always also be transmission by indirect contact.

Airborne transmission

Airborne transmission also involves droplets or particles containing infectious agents, but on a small enough scale that the particles can remain suspended in the air for long periods of time. Infections spread via this route include measles and chicken pox. Prevention is as for droplet transmission.

Parenteral transmission

This is a form of contact transmission, where blood or body fluids containing infectious agents come into contact with mucous membranes or exposed tissue. In healthcare, this can occur through transplantation or infusion, which is why blood and organs for transplantation are screened for bloodborne viruses such as HIV, or through an inoculation injury where blood splashes into the eyes or a used item of sharp equipment penetrates the skin (often called a ‘needlestick’ injury). Transmission is prevented by good practice in handling and disposing of sharps and the appropriate use of protective equipment, including eye protection.

Faecal–oral transmission

This occurs when an infectious agent present in the faeces from the gastrointestinal tract of an infected person is subsequently ingested by someone else and enters their gastrointestinal tract. It is the route of much gastrointestinal illness and water- and foodborne disease. There are often several steps involved; for example, someone with infectious diarrhoea whose hand hygiene is insufficiently effective is likely to contaminate any food they prepare, which will then expose anyone who eats it to infection. Transmission is prevented through isolating any patient with symptoms of gastroenteritis, effective hand hygiene (with soap and water as many of these organisms may be less susceptible to alcohol) by both staff and patients, appropriate use of gloves and aprons, and good food hygiene.

Vector transmission

Many diseases are spread through the action of a vector, most often an insect that travels from one person to another to feed. This route is not currently a concern in healthcare in England, but in parts of the world where malaria is endemic, for example, protecting patients from vectors such as mosquitoes will be an important element of nursing care.

These definitions are useful for considering the different routes by which infectious agents can spread but there is overlap between the different categories: droplet and airborne spread, for example, or indirect contact and faecal–oral. Many agents will be spread by more than one route, or there may be a combination of routes involved. In norovirus infection, for example, the overall mode of spread is faecal–oral