Hospital-acquired infections (HAIs)

Definition

A hospital-acquired infection (HAI), also known as a healthcare-associated infection (HCAI), is often defined as an infection not present or incubating at the time of hospital admission, but acquired 48 hours or more after admission.

NHS England may use the expanded definition of healthcare-associated infection (HCAI) to include:

• Infections occurring ≥48 hours after hospital admission (not present or incubating at admission) OR
• within 3 days of hospital discharge OR
• within 30 days of an operation OR
• within 90 days if a prosthetic implant is involved (e.g. joint replacement, cardiac valve).

Sources and predisposing factors

Environmental factors:

• Air conditioning and piped air: May harbour pathogens such as Legionella pneumophila, especially in stagnant or lukewarm water in complex systems.
• Water supplies: Lukewarm pipes and stagnant water can encourage microbial growth.
• Hospital food: Inappropriate temperatures and delays in transport can increase bacterial load.
• Fomites: Contaminated surfaces may facilitate indirect transmission.

Patient-centred factors:

• Restricted hygiene access: Limited access to washing facilities increases the risk of colonisation and infection.
• Underlying disease and treatment: Immunosuppressive states (e.g. chemotherapy) reduce host defences.
• Close contact areas: High patient turnover in settings like Emergency Departments increases transmission risk.

Devices and procedures:

• Cannulation: The most common cause of hospital-acquired bacteraemia.
• Risk increases with time in situ; peripheral cannulas should be replaced every 48 hours.
• Common pathogens: Staphylococcus aureus, Staphylococcus epidermidis.
• Urinary catheters: Promote urinary stasis and bacterial colonisation, often leading to CAUTIs (Catheter-Associated UTIs).

Common pathogens in HAIs

• Staphylococcus aureus (including MRSA)
• Staphylococcus epidermidis
• Clostridioides difficile
• Pseudomonas aeruginosa
• Escherichia coli
• Enterococcus spp.

Good clinical practice

• Patient isolation: Infected patients should be placed in a side room with dedicated toilet and handwashing facilities.
• PPE: Staff must wear disposable aprons and gloves, removed after patient contact.
• Hand hygiene: Use liquid soap and disposable towels.
• Bare below the elbows policy enhances efficacy.
• Alcohol gel is appropriate in most settings but ineffective against C. difficile spores, use of soap and water in those cases is advised.
• Facemasks: Consider for diseases spread via the respiratory route.

Definitions and methods of infection control

Cleaning:
The removal of foreign material from surfaces or instruments to make them visually clean.

Disinfection:

A process that reduces the number of infectious particles to a level not likely to cause disease.

Disinfectants:

Substances that kill or inhibit microbes. Examples include:

• Iodine: Slow-acting skin antibacterial.
• Chlorhexidine: Particularly effective against staphylococci.
• Isopropyl alcohol (gel): Commonly used, but ineffective against spores like those of C. difficile.

Sterilisation:
Complete inactivation of all infectious agents, achieved primarily through:

• Autoclaving (steam under pressure)
• Irradiation

Control measures summary