5.1 The Chain of Infection and Microorganisms
Key Takeaways
- The chain of infection has six links — breaking any one link prevents infection
- Handwashing breaks the mode of transmission link and is the single most effective prevention measure
- Modes of transmission include direct contact, indirect contact, droplet, airborne, vehicle, and vector
- UTIs are the most common healthcare-associated infection in long-term care facilities
- Elderly residents face increased infection risk due to weakened immunity, chronic diseases, and close living quarters
- Illinois IDPH closely monitors long-term care facilities for infection control compliance
Last updated: March 2026
The Chain of Infection and Microorganisms
Infection control is a critical component of CNA practice and is covered extensively on the INACE. Understanding how infections spread — the chain of infection — is the foundation for all prevention measures. Illinois long-term care facilities are closely monitored by IDPH for infection control compliance, and CNAs play a frontline role in breaking the chain of infection.
Types of Microorganisms
| Type | Description | Examples | CNA Relevance |
|---|---|---|---|
| Bacteria | Single-celled organisms | MRSA, C. diff, E. coli, Strep | Most common cause of healthcare infections |
| Viruses | Require host cells to reproduce | Influenza, COVID-19, Norovirus, Hepatitis | Highly contagious; PPE critical |
| Fungi | Plant-like organisms | Candida (yeast), Athlete's foot, Ringworm | Common in moist areas; keep skin dry |
| Parasites | Live on or in a host | Scabies, lice, pinworms | Require contact precautions |
| Protozoa | Single-celled organisms | Giardia, Cryptosporidium | Spread through contaminated water/food |
The Six Links in the Chain of Infection
Infection can only occur when ALL six links are present. Breaking any one link prevents infection:
| Link | Definition | Example | How to Break |
|---|---|---|---|
| 1. Infectious Agent | The microorganism causing disease | MRSA bacterium | Antibiotics, antiseptics, disinfection |
| 2. Reservoir | Where the organism lives and multiplies | Infected person, contaminated surface | Proper cleaning, isolation protocols |
| 3. Portal of Exit | How the organism leaves the reservoir | Coughing, wound drainage, urine | Covering coughs, proper wound care |
| 4. Mode of Transmission | How the organism travels to a new host | Direct contact, droplets, airborne | Handwashing, PPE, isolation |
| 5. Portal of Entry | How the organism enters a new host | Break in skin, mucous membranes, respiratory tract | Skin integrity, PPE, wound care |
| 6. Susceptible Host | A person who can become infected | Elderly, immunocompromised, malnourished | Nutrition, vaccination, health maintenance |
Modes of Transmission
| Mode | Description | Examples | Prevention |
|---|---|---|---|
| Direct Contact | Physical touching of infected person | Bathing an infected resident, handshakes | Gloves, handwashing, gowns |
| Indirect Contact | Touching contaminated objects (fomites) | Doorknobs, bed rails, call lights | Disinfection, handwashing |
| Droplet | Large respiratory droplets (within 3-6 feet) | Coughing, sneezing, talking | Surgical mask, distancing |
| Airborne | Tiny particles suspended in air | Tuberculosis, measles, chickenpox | N95 respirator, negative pressure room |
| Vehicle | Contaminated food, water, or blood | Foodborne illness, contaminated blood | Food safety, standard precautions |
| Vector | Insects or animals | Mosquitoes (malaria), ticks (Lyme disease) | Pest control, environmental management |
Healthcare-Associated Infections (HAIs)
HAIs are infections acquired in healthcare facilities. They are a major concern in Illinois long-term care:
| HAI Type | Common Organisms | Prevention |
|---|---|---|
| Urinary Tract Infection (UTI) | E. coli, Klebsiella | Proper catheter care, perineal hygiene |
| Respiratory Infection | Influenza, pneumonia | Hand hygiene, vaccination, oral care |
| Skin Infection | MRSA, wound infections | Skin integrity, wound care, clean technique |
| Gastrointestinal | C. diff, Norovirus | Hand hygiene, contact precautions, cleaning |
| Bloodborne | Hepatitis B/C, HIV | Standard precautions, sharps safety |
Factors That Increase Infection Risk in Elderly Residents
| Factor | Why It Increases Risk |
|---|---|
| Weakened immune system | Aging naturally decreases immune function |
| Chronic diseases | Diabetes, heart disease, COPD compromise defenses |
| Poor nutrition | Inadequate protein and vitamins impair healing |
| Immobility | Leads to skin breakdown and pneumonia |
| Invasive devices | Catheters, feeding tubes create entry points |
| Multiple medications | Some drugs suppress immune function |
| Close living quarters | Shared spaces in facilities increase exposure |
| Cognitive impairment | Residents with dementia may not practice hygiene |
Test Your Knowledge
Which link in the chain of infection does handwashing PRIMARILY break?
A
B
C
D
Test Your Knowledge
Which mode of transmission requires an N95 respirator for protection?
A
B
C
D
Test Your Knowledge
The most common type of healthcare-associated infection (HAI) in long-term care facilities is:
A
B
C
D