7.1 The Chain of Infection

The Chain of Infection

Quick Answer: The chain of infection has six links — infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host. Break any single link and infection cannot occur. For the Indiana CNA, the most actionable links are the reservoir (cleaning surfaces), the mode of transmission (hand hygiene and PPE), and the susceptible host (protecting immunocompromised residents).

Infection control is 10% of the Indiana CNA written exam and shows up on the clinical skills evaluation as hand hygiene critical steps. Every infection in a long-term care facility follows the same six-link chain. Understand the chain and you can break it at any point — that is the foundation of every precaution you will practice.

The Six Links

1. Infectious Agent (the pathogen)

The microorganism that causes disease — bacteria (MRSA, C. diff, TB), viruses (influenza, SARS-CoV-2, hepatitis B, HIV, varicella), fungi, or parasites (scabies, pediculosis). Each pathogen has different survival characteristics: C. diff forms hardy spores that live on surfaces for months; HIV dies quickly outside the body. Knowing the agent drives PPE choice and disinfectant selection.

Break the chain: Use the correct EPA-registered disinfectant for the pathogen. C. diff requires a sporicidal disinfectant (often bleach-based) — standard quaternary disinfectants do not kill spores. Indiana LTC facilities post approved disinfectant lists near the cleaning cart; check the label before using.

2. Reservoir (where the pathogen lives)

The reservoir is where the organism normally lives and multiplies — the resident (an infected wound, the digestive tract carrying C. diff), the environment (bedrails, call lights, reusable equipment, privacy curtains), food, or water. The human reservoir may be symptomatic (sick) or asymptomatic — an MRSA carrier who shows no signs is still a reservoir.

Break the chain: Clean high-touch surfaces (bedrails, overbed tables, call lights, door handles, privacy curtain ties) between residents and at least once per shift. Soiled linen is a reservoir — bag it at the point of origin, do not sort or rinse it in the resident's room.

3. Portal of Exit (how the pathogen leaves the reservoir)

The route by which the organism leaves the host — respiratory tract (cough, sneeze), gastrointestinal tract (stool, vomit), genitourinary tract (urine), skin (wound drainage, lesions), blood (needlestick, bleeding), or mucous membranes.

Break the chain: Cover coughs and sneezes with the elbow (not hands); contain stool and vomit promptly; contain wound drainage with dressings (the CNA observes but does NOT apply or remove dressings per 410 IAC 16.2 Standard 14); use sharps containers for needles and lancets — never recap a needle.

4. Mode of Transmission (how it travels)

The way the pathogen moves from reservoir to the new host. Three modes are tested on the Indiana CNA exam:

• Contact transmission — the most common route in LTC. Direct contact is skin-to-skin (turning a resident with MRSA). Indirect contact is via a contaminated object (shared BP cuff, unwashed stethoscope, soiled linen). MRSA, VRE, C. diff, scabies, and pediculosis spread this way.
• Droplet transmission — large respiratory droplets travel short distances (about 3–6 feet) through the air when a resident coughs, sneezes, talks, or is suctioned. Influenza, mumps, rubella, pertussis, and meningococcal meningitis spread by droplet.
• Airborne transmission — tiny infectious nuclei stay suspended in air for long distances. TB, measles, and varicella (chickenpox) spread airborne. These require a negative-pressure AIIR room and an N95 respirator — beyond the CNA's scope; the CNA assists with transfer and does NOT enter without a fit-tested N95.

Break the chain: Hand hygiene is the single most effective way to break contact transmission. For droplet, use a surgical mask and stay 6 feet away when possible. For airborne, the CNA's job is to support the facility's AIIR protocol — do not enter without an N95 and confirmed fit-test.

5. Portal of Entry (how it gets into the new host)

The route into the susceptible host — breaks in skin (cuts, pressure ulcers, IV sites), mucous membranes (eyes, nose, mouth), respiratory tract, GI tract, urinary tract (catheter), or reproductive tract.

Break the chain: Cover all breaks in the resident's skin with dressings; use sterile technique for catheter care; keep the urinary drainage bag below bladder level and off the floor; wear gloves for any contact with mucous membranes or non-intact skin; never touch your own eyes, nose, or mouth with gloved hands.

6. Susceptible Host (who gets infected)

The person at risk — elderly residents, immunocompromised residents, those with chronic disease (diabetes, COPD, kidney disease), residents with invasive devices (Foley catheters, IV lines, feeding tubes), malnourished residents, and those on antibiotics (which disrupt normal gut flora and allow C. diff overgrowth).

Break the chain: Protect the host through good nutrition and hydration, prompt reporting of early infection signs (fever, redness, drainage, change in mental status), repositioning to prevent pressure ulcers (a portal of entry), and strict adherence to transmission-based precautions. The CNA does not boost the immune system directly — you protect it by preventing exposure.

Putting It Together on the Indiana CNA Exam

The exam often presents a scenario and asks which link you are breaking with a specific action. Hand hygiene breaks the mode of transmission link. Cleaning the bedside table breaks the reservoir link. Putting a mask on a coughing resident breaks the portal of exit link. Dressing a pressure ulcer correctly breaks the portal of entry link. Identifying the link from the action — and vice versa — is the testable skill.

In an Indiana LTC facility, the chain is real, not abstract. A C. diff resident on antibiotics (susceptible host) sheds spores in stool (portal of exit), which contaminate the bedrail (reservoir). A CNA who skips hand hygiene carries spores to the next resident (mode of transmission), whose pressure ulcer (portal of entry) becomes infected. Break the chain at hand hygiene and the next resident never gets exposed.