5.1 Chain of Infection and Standard Precautions
Key Takeaways
- The chain of infection has six links: causative agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host - breaking any one link stops the infection.
- Standard Precautions apply to ALL residents and ALL body fluids (blood, secretions, excretions, non-intact skin, mucous membranes) EXCEPT sweat, regardless of suspected infection status.
- Hand hygiene is the single most effective infection-control action; the CDC and WHO require it before resident contact, before a clean/aseptic task, after body-fluid exposure risk, after resident contact, and after touching resident surroundings.
- Alcohol-based hand rub (60-95% alcohol) is preferred for most situations, but soap and water must be used when hands are visibly soiled, after toileting, and for residents with C. difficile or norovirus because alcohol does not kill spores.
- Effective handwashing with soap requires at least 20 seconds of friction over all hand surfaces under running water (CDC standard).
Chain of Infection and Standard Precautions
Quick Answer: An infection only spreads when all six links of the chain are intact: a causative agent, a reservoir, a portal of exit, a mode of transmission, a portal of entry, and a susceptible host. CNAs break the chain primarily through hand hygiene and Standard Precautions, which apply to every resident and every body fluid except sweat.
Infection control is the single largest source of NNAAP skills-test deductions and one of the highest-yield areas on the NC written exam. Two-thirds of the questions in this chapter can be answered correctly if you can (a) draw the chain of infection, (b) recite the WHO 5 Moments for hand hygiene, and (c) know when alcohol rub does not work.
The Six-Link Chain of Infection
The Centers for Disease Control and Prevention (CDC) describes infection as a chain. If a CNA breaks any link, the infection cannot spread.
| # | Link | Plain-English meaning | CNA action that breaks the link |
|---|---|---|---|
| 1 | Causative agent | The germ itself: bacteria, virus, fungus, parasite | Disinfect surfaces; clean equipment between residents |
| 2 | Reservoir | Where the germ lives: people, soiled linen, contaminated water, soil | Empty bedpans promptly; bag and remove soiled linen; cover wounds |
| 3 | Portal of exit | How the germ leaves the reservoir: respiratory secretions, blood, urine, stool, wound drainage | Cough into the elbow; contain body fluids; close drainage bags |
| 4 | Mode of transmission | How the germ travels: contact (direct/indirect), droplet, airborne, vehicle (food/water), vector (insects) | Hand hygiene; PPE; isolation precautions; safe food handling |
| 5 | Portal of entry | How the germ enters the next person: broken skin, mouth, nose, eyes, catheter sites | Keep skin intact; provide perineal care; cover open wounds; do not touch face with gloves |
| 6 | Susceptible host | A person who can become sick: older adults, immunocompromised, malnourished, those with chronic disease | Encourage vaccination, fluids, nutrition, and rest; report changes to the nurse |
Modes of transmission (memorize):
- Contact - direct touch or indirect contact with contaminated objects (MRSA, VRE, C. difficile, scabies)
- Droplet - large respiratory droplets that travel up to 3-6 feet and fall to the ground (influenza, pertussis, mumps, meningococcal disease)
- Airborne - small droplet nuclei that stay suspended in air for hours and travel on air currents (tuberculosis, measles, varicella/chickenpox)
- Vehicle - contaminated food, water, blood, or medication (Salmonella, hepatitis A)
- Vector - insects or animals (mosquitoes for West Nile; ticks for Lyme)
Standard Precautions: The Default Setting
The CDC's Standard Precautions replaced the older Universal Precautions in 1996 and apply to all residents at all times, whether or not an infection is suspected. CNAs treat the following as potentially infectious:
- Blood
- All body fluids, secretions, and excretions EXCEPT sweat (whether or not they contain visible blood)
- Non-intact skin (cuts, abrasions, wounds, IV sites)
- Mucous membranes (eyes, nose, mouth, perineum)
Sweat is the one body fluid not classified as infectious for Standard Precautions purposes (CDC 2007 Isolation Guideline).
Core elements of Standard Precautions:
- Hand hygiene - before and after every resident contact (see WHO 5 Moments below)
- Personal protective equipment (PPE) - gloves, gown, mask, eye protection based on the task
- Respiratory hygiene / cough etiquette - cover coughs, mask symptomatic residents, hand hygiene after
- Safe injection practices - never recap or reuse needles; one needle, one syringe, one time
- Sharps safety - dispose immediately at point of use in a puncture-resistant container
- Safe handling of contaminated equipment and linen - bag at point of use; do not shake linen
- Environmental cleaning and disinfection
The WHO 5 Moments for Hand Hygiene
The World Health Organization (WHO) defines the five moments at which hand hygiene must occur. The NC NNAAP skills test deducts points for missing any of them.
| Moment | When | Why |
|---|---|---|
| 1 | Before touching a resident | Protect the resident from germs on the CNA's hands |
| 2 | Before a clean / aseptic procedure (catheter care, wound care, feeding) | Protect the resident from germs entering their body |
| 3 | After body-fluid exposure risk (perineal care, bedpan, vomit) | Protect the CNA and the environment |
| 4 | After touching a resident | Protect the CNA and other residents |
| 5 | After touching resident surroundings (bed rails, call light, overbed table) | Surfaces are contaminated even when the resident was not touched |
Alcohol-Based Hand Rub vs. Soap and Water
The CDC's Guideline for Hand Hygiene in Health-Care Settings lists alcohol-based hand rub (ABHR, 60-95% alcohol) as the preferred method when hands are not visibly soiled because it is faster, kills more organisms, and damages skin less. However, it does not kill bacterial spores.
Use SOAP AND WATER (not alcohol rub) when:
- Hands are visibly soiled with blood or body fluids
- After using the restroom
- Caring for a resident with C. difficile (spore-forming bacterium) - alcohol does NOT kill C. diff spores
- Caring for a resident with norovirus (non-enveloped virus that resists alcohol)
- Before eating
Correct soap-and-water technique (CDC):
- Wet hands with warm running water with fingers pointed down.
- Apply soap.
- Lather and rub all surfaces - palms, backs, between fingers, under nails - for at least 20 seconds (about the time it takes to hum Happy Birthday twice).
- Rinse with fingers still pointed down.
- Dry with a clean paper towel.
- Use the same paper towel to turn off the faucet so you do not re-contaminate clean hands.
Correct alcohol-rub technique: Apply a palm-sized amount, rub all surfaces of both hands and fingers, and continue rubbing until the product is fully dry - usually 15-20 seconds. If your hands feel dry in under 10 seconds, you did not use enough product.
Putting It Together: Breaking the Chain
Almost every infection-control exam item asks the same underlying question: Which link of the chain does this action break, and is it the highest-priority action? For example, wearing gloves during perineal care breaks the portal of exit and mode of transmission links. Disposing of a soiled brief breaks the reservoir link. Handwashing after removing gloves breaks the mode of transmission link a second time, because gloves frequently have microscopic punctures.
A North Carolina CNA is caring for a resident newly diagnosed with Clostridioides difficile (C. diff) diarrhea. The CNA has just removed gloves after providing perineal care. Which hand hygiene method is REQUIRED?
Standard Precautions, as defined by the CDC, treat ALL of the following as potentially infectious EXCEPT: