Safety Services


Transmission Routes

For pathogens to cause infection and disease they need a transmission route. The page details the different transmission routes.

Transmission Routes

When working with pathogenic microorganisms or materials that could contain pathogenic microorganisms, there is a risk of laboratory-acquired infections. There is also a risk of exposure to pathogens through incidental exposure e.g. working on water systems there may be a risk of exposure to legionella

Infection and disease require 3 elements to succeed. These include; a pathogen, transmission route and a host. The host can be human, animal or plant. When all three elements are present there is a potential for infection and disease to occur, however it is not always guaranteed. There are a number of factors affecting infection or disease.

If one of the three elements is removed, infection and disease arenot possible. At UCL, research work involves working with pathogen organisms and materials that could potentially contain infectious pathogens. Therefore, it is not always possible to remove the pathogen or the host, so the transmission route has to be managed.

Below is a description of the different transmission routes with some examples.


Ingestion of pathogenic organisms through eating and drinking, mouth pipetting transfer of microorganisms from hand to the mouth through contaminated fingers, e.g. Salmonella food poisoning, cholera from drinking infected water, Transmissible Spongiform Encephalitis (TSEs).

Controls: regular hand washing, no eating drinking or mouth pipetting in the laboratory avoid touching the face with gloves on.


Inhalation of infectious aerosols created through activities such as pipetting, vortexing, centrifugation. e.g. COVID-19, Influenza

Control: minimise aerosols and use equipment that can contain aerosols e.g. MSCs and centrifuges with rotors/ buckets / cups that have a sealable lid.


Percutaneous exposure through accidental cuts or puncture wounds with sharp instruments, bites, scratches or through broken skin as a result of skin conditions such as eczema or psoriasis. TSE's, Human Immunodeficiency Virus (HIV), Hepatitis B

Control: minimise the use of sharps, consider cut-resistant gloves, cover broken skin with a waterproof dressing especially when on the hands and wear gloves

Mucous membranes

Mucous Membranes, exposure through splashes to mucous membranes including the noses and eyes. transfer of microorganisms to mucous membranes can occur through contaminated fingers or articles and splashes e.g. HIV, Hepatitis B

Control: avoid touching the face with gloves, wear goggles, safety specs with side shields or visors.

Factors affecting infection or disease.

There are a number of factors that affect the likelihood of successful disease transmission.

  • Pathogenicity of the organism
  • Infective dose
  • Immuno-competence of the person exposed
  • Route of transmission

All activities working with biological agents should assess the risk of exposure and transmission to determine the correct controls to have in place to protect people and the environment.

Last updated: Tuesday, January 17, 2023