Key Takeaways
- The chain of infection has 6 links: agent, reservoir, exit, transmission, entry, susceptible host
- All 6 links must be present for infection to spread - break any link to prevent transmission
- Pathogens include bacteria, viruses, fungi, parasites, and prions
- Modes of transmission include contact (direct/indirect), droplet, airborne, and vector
- Hand hygiene is the most effective way to break the chain of infection
Chain of Infection
Understanding the chain of infection is essential for preventing the spread of disease in healthcare settings. By breaking any link in this chain, CNAs help protect patients, coworkers, and themselves.
What is the Chain of Infection?
The chain of infection describes the six elements required for an infection to spread from one person to another. All six links must be present for infection to occur:
| Link | Description | Example |
|---|---|---|
| 1. Infectious Agent | The pathogen (germ) | Bacteria, virus, fungus, parasite |
| 2. Reservoir | Where the germ lives | Humans, animals, environment |
| 3. Portal of Exit | How germ leaves reservoir | Respiratory secretions, blood, feces |
| 4. Mode of Transmission | How germ travels | Direct contact, droplets, airborne |
| 5. Portal of Entry | How germ enters new host | Mucous membranes, wounds, inhalation |
| 6. Susceptible Host | Person who can get infected | Elderly, immunocompromised, infants |
Types of Infectious Agents
Pathogens are microorganisms that cause disease:
| Type | Examples | Diseases Caused |
|---|---|---|
| Bacteria | Staph, Strep, E. coli, C. diff | MRSA, pneumonia, UTIs |
| Viruses | Influenza, COVID-19, Norovirus | Flu, respiratory illness, gastroenteritis |
| Fungi | Candida, Tinea | Yeast infections, ringworm |
| Parasites | Lice, scabies, pinworms | Infestations |
| Prions | Abnormal proteins | Creutzfeldt-Jakob disease |
Common Reservoirs
Reservoirs are places where pathogens live and multiply:
| Reservoir Type | Examples |
|---|---|
| Humans | Infected patients, carriers, healthcare workers |
| Animals | Pets, pests (rodents, insects) |
| Environment | Contaminated surfaces, water, food, equipment |
Portals of Exit
Ways pathogens leave the reservoir:
| Portal of Exit | Examples |
|---|---|
| Respiratory | Coughing, sneezing, talking |
| Gastrointestinal | Feces, vomit |
| Blood/Body fluids | Open wounds, needlesticks |
| Urinary | Urine |
| Skin | Skin lesions, wound drainage |
Modes of Transmission
How pathogens travel from one host to another:
| Mode | Description | Example |
|---|---|---|
| Contact - Direct | Touching infected person | MRSA from skin contact |
| Contact - Indirect | Touching contaminated object | C. diff from bedrails |
| Droplet | Large droplets (>5 microns), travel <6 feet | Influenza, COVID |
| Airborne | Small particles (<5 microns), travel far | TB, measles, chickenpox |
| Vector | Insect or animal carrier | Lyme disease (ticks) |
| Common vehicle | Contaminated food/water | Salmonella, Hepatitis A |
Portals of Entry
How pathogens enter a new host:
| Portal of Entry | Examples |
|---|---|
| Respiratory tract | Inhaling contaminated air |
| Mucous membranes | Eyes, nose, mouth contact |
| Breaks in skin | Wounds, IV sites, surgical sites |
| Gastrointestinal | Ingesting contaminated food/water |
| Urinary tract | Catheter insertion |
| Placenta | Mother to fetus |
Susceptible Hosts
People at higher risk for infection:
| Risk Factor | Why More Susceptible |
|---|---|
| Elderly | Weakened immune system |
| Infants | Immature immune system |
| Chronic disease | Body resources depleted |
| Surgery patients | Breaks in skin barrier |
| Immunocompromised | HIV, cancer treatment, transplant |
| Diabetics | Impaired circulation and healing |
| Malnourished | Weakened defenses |
Breaking the Chain
CNAs can break the chain at every link:
| Link | How CNAs Break It |
|---|---|
| Infectious agent | Cleaning, disinfecting, sterilizing |
| Reservoir | Proper waste disposal, environmental cleaning |
| Portal of exit | Covering coughs, containing body fluids |
| Transmission | Hand hygiene, PPE, isolation precautions |
| Portal of entry | Wound care, sterile technique |
| Susceptible host | Nutrition, encouraging vaccines |
How many links are in the chain of infection?
What is the MOST effective way for CNAs to break the chain of infection?
Which of the following is a mode of transmission?