2. The chain of infection and standard precautions
The chain of infection
Infection needs a complete chain. Break any link and transmission stops.
- Infectious agent — bacteria, viruses, fungi (for example blood-borne viruses, respiratory viruses, oral flora).
- Reservoir — a person, a biofilm in a waterline, a damp instrument tray, a contaminated cloth.
- Portal of exit — blood, saliva, respiratory droplets, contaminated surfaces.
- Mode of transmission — contact, droplets, aerosols, sharps injury, contaminated instruments.
- Portal of entry — mucosa, non-intact skin, respiratory tract, percutaneous injury.
- Susceptible host — every patient and every staff member; some are at higher risk.
Standard precautions
Treat blood and body fluids from every patient as potentially infectious. Do not guess who is “low risk”. Standard precautions include hand hygiene, appropriate PPE, safe sharps, cleaning of the clinical environment, decontamination of reusable devices, spillages and waste, and staff immunisation.
Single-use vs reusable
If an item is labelled single-use, it is used once and discarded. Do not reprocess it. Reusable devices must be decontaminated according to the manufacturer’s instructions for use (IFU) and your validated process. If the IFU and your machine capability do not match, that device should not be used until the gap is resolved.
Biofilm and protein
Organic soil (blood, saliva, tissue) shields microbes from disinfectant and steam. Cleaning is not optional decoration before sterilisation — it is the step that makes sterilisation possible. Protein residue testing exists because visual inspection alone is not enough.