4.1 Infection Control & Asepsis

The Cycle of Infection

Preventing healthcare-associated infections (HAIs) starts with understanding how disease spreads. The cycle of infection, also called the chain of infection, has six links, and breaking any single link stops transmission:

1. Infectious agent - the pathogen itself (bacterium, virus, fungus, protozoan, or prion).
2. Reservoir - where the agent lives and multiplies (an infected person, an animal, contaminated equipment, water, or soil).
3. Portal of exit - how the agent leaves the reservoir (respiratory secretions, blood, feces, urine, wound drainage).
4. Mode of transmission - how it travels: contact (direct or indirect), droplet, airborne, a common vehicle (food, water, blood), or a vector (insect).
5. Portal of entry - how it enters the next person (broken skin, mucous membranes, the respiratory or GI tract, an IV site).
6. Susceptible host - a person with lowered resistance (immunocompromised, elderly, neonatal, diabetic, or chronically ill).

The radiographer breaks the chain most often at the mode of transmission (through hand hygiene, PPE, and disinfection) and by protecting the susceptible host. Of all measures, hand hygiene is the single most effective way to prevent HAIs, a point the ARRT exam tests repeatedly.

Standard and Transmission-Based Precautions

Standard Precautions are applied to every patient, every time, on the assumption that all blood, body fluids, secretions, and excretions (except sweat), non-intact skin, and mucous membranes may carry pathogens. Beyond hand hygiene and PPE, Standard Precautions also include respiratory hygiene and cough etiquette for symptomatic patients, safe injection practices (one needle, one syringe, one time per patient), and cleaning and disinfecting the imaging table, image receptors, and shared equipment between patients. When a specific organism needs more, one of three transmission-based categories is added on top of Standard Precautions. Knowing the correct PPE for each category is high-yield:

The classic ARRT trap is tuberculosis: it is airborne, not droplet, so it demands an N95 respirator and a negative-pressure room, never a plain surgical mask. Droplet organisms such as influenza travel only a few feet before falling, so a surgical mask worn nearby is enough. Because C. difficile and norovirus resist alcohol, hands must be washed with soap and water, not alcohol rub, after caring for those contact-precaution patients.

Medical vs. Surgical Asepsis

Two standards of cleanliness apply in radiography, and the exam expects you to separate them:

• Medical asepsis (clean technique) - practices that reduce the number and spread of microorganisms without eliminating all of them: hand hygiene, disinfecting the table, wearing clean (non-sterile) gloves, and isolation precautions.
• Surgical asepsis (sterile technique) - practices that eliminate ALL microorganisms, including bacterial spores. Required for invasive work such as the sterile field, urinary catheterization, lumbar puncture, arthrography, and angiography.

These fit into a levels-of-asepsis hierarchy, ranked from strongest to weakest killing power:

Sterilization > high-level disinfection > antisepsis > sanitization/cleaning

• Sterilization destroys all microbial life, including spores (steam autoclave, ethylene oxide gas, dry heat, or chemical/cold sterilization); required for anything entering sterile tissue or the bloodstream.
• High-level disinfection kills most pathogens on inanimate surfaces but not all spores (imaging tables, cassettes, lead aprons).
• Antisepsis applies a germicide to living tissue, such as prepping the skin before venipuncture.
• Sanitization/cleaning simply lowers microbial counts to safe levels by physically removing soil and debris.

Hand Hygiene and PPE Order

Hand hygiene is done with an alcohol-based hand rub (60-95% alcohol) in most situations because it is faster and kills more organisms than plain soap. Use soap and water instead when hands are visibly soiled or after caring for patients with C. difficile or norovirus, whose spores resist alcohol. Gloves are never a substitute for hand hygiene; wash your hands after removing them.

The order of putting on and taking off PPE is tested directly:

• Donning (putting on): gown, then mask or N95 respirator, then goggles/face shield, then gloves.
• Doffing (taking off), most-contaminated item first: gloves, then goggles/face shield, then gown, then mask/respirator. The respirator comes off last, after you leave the patient's room, so you never inhale airborne particles while unprotected.

A worked example

A patient in a negative-pressure room with active TB needs a portable chest film. The radiographer performs hand hygiene, dons a fit-tested N95 respirator, covers the image receptor with a clean barrier, keeps the door closed to preserve negative pressure, positions and exposes the patient, then disinfects the mobile unit after leaving and washes again. Choosing the N95 over a surgical mask and terminally cleaning the machine between patients is exactly the reasoning ARRT patient-care items reward.

Common traps

• TB is airborne - it needs an N95 plus a negative-pressure room, not a surgical mask.
• Alcohol rub fails against C. difficile spores - use soap and water.
• Sweat is the one body fluid not covered by Standard Precautions.
• Surgical asepsis kills spores; medical asepsis only reduces microbial numbers.