Microbiology and Infection Control
What this domain tests
Microbiology and infection control tests the chain of infection, transmission routes, standard and transmission-based precautions, cleaning and sterilisation, and antibiotic stewardship. Questions often present a scenario and ask which precaution or action is correct.
Core rules
- Chain of infection: infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host. Breaking any link prevents transmission.
- Contact precautions cover direct and indirect contact; droplet precautions cover large respiratory particles travelling short distances; airborne precautions cover small particles that remain suspended, such as tuberculosis, measles and varicella.
- Standard precautions apply to every patient: hand hygiene, gloves, gown, eye protection and safe sharps handling.
- The five hand-hygiene moments are before patient contact, before an aseptic task, after body-fluid exposure risk, after patient contact, and after touching surroundings.
- Alcohol-based rub is preferred for routine hand hygiene when hands are not visibly soiled. Use soap and water for Clostridioides difficile, norovirus and visible soil.
- Sterilisation destroys all microorganisms including spores; disinfection reduces pathogens but may not kill spores.
- Stewardship means the right drug, dose, route and duration; culture before antibiotics when safe; and never sharing antibiotics.
Worked example
A patient develops watery diarrhoea after five days of broad-spectrum antibiotics. The likely diagnosis is Clostridioides difficile infection. The organism forms spores that survive alcohol. Place the patient in a single room with contact precautions, wear gloves and gown, use soap and water for hand hygiene, clean equipment with a chlorine-based agent, and avoid antiperistaltic drugs. The reasoning links antibiotic exposure to disrupted colon flora, then selects sporicidal measures rather than alcohol rub.
Traps that cost marks
- Using alcohol gel for C. difficile or norovirus.
- Applying airborne precautions for influenza, which is droplet spread, or contact precautions for measles, which is airborne.
- Treating colonisation as infection without clinical signs.
- Sending cultures after antibiotics when the patient is stable and culture could have been taken first.
- Forgetting that standard precautions apply even when a patient has no known infection.