5.1 The Chain of Infection and Microorganisms
Key Takeaways
- The chain of infection has six links; breaking any one link stops the spread, and the mode-of-transmission link is the one a CNA controls most
- Microbes that cause disease are called pathogens; bacteria (MRSA, C. diff, E. coli) cause most healthcare infections, while viruses (flu, norovirus, COVID-19) are highly contagious
- Modes of transmission tested on the INACE are direct contact, indirect contact (fomites), droplet, airborne, vehicle (food/water), and vector (insects)
- Urinary tract infection is the most common healthcare-associated infection in long-term care, usually linked to indwelling catheters
- Elderly residents are highly susceptible hosts because of immunosenescence, chronic disease, malnutrition, immobility, and invasive devices
- The INACE is an 85-question written test plus a skills evaluation administered by SIU-Carbondale for IDPH; infection control appears in the Basic Nursing Skills duty area
Why Infection Control Dominates the INACE
Infection control is the single most heavily weighted clinical topic on the Illinois exam. The Illinois Nurse Aide Competency Examination (INACE) is an 85-question written test taken in 90 minutes, paired with a hands-on skills evaluation, administered by Southern Illinois University-Carbondale (SIU-C) under contract to the Illinois Department of Public Health (IDPH). You must pass both parts within 24 months of finishing training to be listed on the Illinois Health Care Worker Registry.
Infection content sits inside the Basic Nursing Skills duty area, and hand hygiene threads through nearly every hands-on skill the evaluator scores.
Microorganisms (Pathogens) You Must Recognize
A microbe that causes disease is a pathogen. Non-pathogens (normal flora) live on us harmlessly until they reach the wrong place. Know which class each named organism belongs to:
| Type | Key Trait | Tested Examples | CNA Action |
|---|---|---|---|
| Bacteria | Single-celled; many spore-form | MRSA, C. difficile, E. coli, Klebsiella | Most HAIs; hand hygiene + contact precautions |
| Viruses | Need a host cell to reproduce | Influenza, COVID-19, norovirus, hepatitis B/C, HIV | Highly contagious; PPE and vaccination |
| Fungi | Thrive in warm, moist areas | Candida (thrush, yeast), ringworm, athlete's foot | Keep skin clean and DRY |
| Parasites | Live on or in a host | Scabies, lice, pinworms | Contact precautions; treat linens |
| Protozoa | Single-celled; water/food spread | Giardia, Cryptosporidium | Food and water safety |
The Six Links in the Chain of Infection
Infection occurs only when all six links are present and connected. Break any single link and the infection cannot spread. CNAs most often break link 4 (transmission) through hand hygiene, but a strong answer recognizes the full chain.
| # | Link | Plain Definition | Real LTC Example | How a CNA Breaks It |
|---|---|---|---|---|
| 1 | Infectious agent | The pathogen itself | C. difficile bacterium | Disinfection, antibiotics (nurse), cleaning |
| 2 | Reservoir | Where it lives and multiplies | Infected resident, soiled brief, bedrail | Cleaning, isolation, pest control |
| 3 | Portal of exit | How it leaves the reservoir | Stool, urine, cough droplets, wound drainage | Cover coughs, contain drainage, hand hygiene |
| 4 | Mode of transmission | How it travels to a new host | Contaminated hands, shared equipment | Hand hygiene, PPE, isolation |
| 5 | Portal of entry | How it enters the new host | Broken skin, catheter, mucous membranes | Skin integrity, aseptic technique, PPE |
| 6 | Susceptible host | A person who can get infected | Frail elderly resident | Nutrition, hydration, vaccination, mobility |
Worked Scenario
A resident with active norovirus vomits. The virus (agent) lives in the resident's GI tract (reservoir), exits in vomit/stool (exit), reaches your ungloved hands (transmission), and you then feed a frail roommate who swallows it (entry into a susceptible host). Donning gloves and washing with soap and water after breaks the transmission link and stops the outbreak.
Modes of Transmission
- Direct contact — skin-to-skin (bathing, repositioning). Break with gloves and hand hygiene.
- Indirect contact — a contaminated object called a fomite (call light, doorknob, bedrail, BP cuff). Break with disinfection between residents.
- Droplet — large respiratory droplets traveling about 3–6 feet (flu, pertussis). Break with a surgical mask.
- Airborne — tiny particles that hang in the air (tuberculosis, measles, chickenpox). Break with an N95 respirator and a negative-pressure room.
- Vehicle — contaminated food, water, or blood. Break with food safety and standard precautions.
- Vector — insects or animals (mosquitoes, ticks). Break with pest control.
Healthcare-Associated Infections (HAIs) in Illinois Long-Term Care
An HAI is an infection a resident did NOT have on admission but acquired in the facility. IDPH tracks HAI rates, and CNAs are the frontline defense. Memorize the most common HAI and its prevention:
| HAI | Common Organisms | Top Prevention by the CNA |
|---|---|---|
| Urinary tract infection (UTI) — #1 in LTC | E. coli, Klebsiella | Catheter care, perineal hygiene front-to-back, keep bag below bladder, fluids |
| Respiratory (pneumonia, flu) | Influenza, S. pneumoniae | Hand hygiene, oral care, mobility, vaccination |
| Skin/wound | MRSA | Reposition q2h, keep skin clean/dry, clean technique |
| Gastrointestinal | C. diff, norovirus | Soap-and-water handwashing, contact precautions, bleach cleaning |
| Bloodborne | Hepatitis B/C, HIV | Standard precautions, never recap needles |
Why UTIs lead: indwelling urinary catheters create a direct portal of entry into a normally sterile tract, and many LTC residents have them long-term. Expect a test item asking for the most common LTC HAI — the answer is UTI, not pneumonia.
Why Elderly Residents Are Susceptible Hosts
| Risk Factor | Mechanism |
|---|---|
| Weakened immunity (immunosenescence) | Aging blunts the immune response |
| Chronic disease | Diabetes, COPD, heart failure lower defenses |
| Poor nutrition/hydration | Low protein and fluids slow healing |
| Immobility | Leads to pressure injuries and pneumonia |
| Invasive devices | Catheters and feeding tubes bypass natural barriers |
| Cognitive impairment | Dementia residents may not perform hygiene |
| Communal living | Shared dining and activity rooms increase exposure |
Common trap: an item may ask what a CNA can do about the susceptible host link — the answer is supportive care (nutrition, hydration, mobility, oral care, encouraging vaccination), NOT antibiotics, which a CNA never administers.
Which link in the chain of infection does a CNA break MOST directly by performing hand hygiene?
A resident on contact precautions for scabies coughs onto a shared bedside table that the next resident later touches. The table is acting as which part of the chain of infection?
Which is the MOST common healthcare-associated infection in long-term care facilities?
A new CNA asks how many questions the Illinois written competency exam (INACE) contains and who administers it. The correct answer is: