Hospital acquired infections

The hospital is a crowded environment full of susceptible patients where infections can and are easily spread.

What makes up a hospital acquired infection (HAI), also known as a nosocomial infection?

A HAI is defined as an infection occurring >48 hours after admission to hospital.

It has an overall prevalence of ~10% with inpatient stays, and it increases with the length of stay, interventions performed and co-morbidities already present.

It places a financial burden of approximately £1 billion on the NHS as it increases the morbidity and length of stay and thus cost of care too.

Common nosocomial infections

1. UTIs - the most common nosocomial infection (~25%).
2. Chest/respiratory infections - most notably hospital acquired pneumonia (HAP). RTIs following general anaesthetics or mechanical ventilation.
3. Bloodstream infections may also be present after cannulation or venepuncture (these are most dangerous).
4. Surgical site infections
5. Antbiotic associated diarrhoea - antibiotics may lead to C. dificile colitis.

Pathophysiology

3 things are needed for a nosocomial infection to occur:

1. Microorganism
2. Immunocompromised host
3. Vector of transmission - may be medical devices, respiratory droplets, fomite transmission etc.

⚠️ Risk factors

Host risk factors

1. Extremes of age
2. Immunocompromised status

3. Surgery
4. Peripheral vascular disease

Environmental risk factors

1. Contaminated water systems - Legionella is especially prevalent when temperature of water storage keeps changing.
2. Physical layout - open beds that are close together for example.
3. Air-conditioning systems - Legionella is more common when places use cooling towers.

Antimicrobials

Medical devices

Any medical device introduced into the body may develop a biofilm. Medical devices are involved in ~60% of nosocomial infections.

Some examples include:

1. Peripheral IV line - should not be inserted for more than 3 days. Has low risk but risk is still present.
2. Central venous catheter - can be inserted for weeks.
3. Hickman line - used in cancer therapy and can stay for months - a year. A biofilm that forms in a Hickman catheter is very difficult to eradicate.
4. Urinary catheter - very commonly cause CAUTI, as the urethral area is contaminated with bacteria and can colonise the catheter to form a biofilm.
5. Tracheostomy tube - associated with HAP.
6. Ventilator - associated with VAP.

Specific HAIs

Methicillin resistant staphylococcus aureus (MRSA)

MRSA is found on cutaneous surfaces, but can be introduced internally and produce infection when there are breaches in the skin as with surgical wounds or by medical devices. It can lead to septicaemia, however it usually presents as pustular skin infections.

Patients awaiting elective admissions are screened for MRSA with nasal swabs, skin lesion/wound swabs.

The following antibiotics are commonly used for MRSA:

1. Vancomycin
2. Teicoplanin
3. Linezolid

Clostridium difficile

Antibiotics and PPIs can produce C. difficile colitis as it suppresses the gut flora.

The Public Health England Severity Scale can be used to classify the severity of c. difficile colitis:

🧰 Management:

Depends on the episode of infection (first, recurrent, or life-threatening).

• Life-threatening C.difficile colitis:
• Oral vancomycin + IV metronidazole
• Surgery may be considered