Chain of Infection, Standard & Transmission-Based Precautions & PPE
Key Takeaways
- The chain of infection has six links: infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host — breaking any one link stops disease spread.
- Standard precautions (hand hygiene, gloves, and eye/face protection as indicated) apply to every patient, every time, regardless of diagnosis.
- CDC's PPE donning order is gown, mask or respirator, goggles or face shield, then gloves; doffing order is gloves, goggles or face shield, gown, then mask or respirator.
- Airborne precautions (TB, measles, varicella) require a fit-tested N95 or higher respirator and a negative-pressure room; droplet precautions (influenza, pertussis, meningitis) require only a surgical mask.
- Alcohol-based hand sanitizer does not kill C. difficile spores, so hands must be washed with soap and water after caring for a patient with C. diff.
The Chain of Infection
Every infection that develops in a healthcare setting follows the same six-link sequence, known as the chain of infection. Break any single link and transmission stops — this is the theoretical basis for every precaution, glove, and hand-hygiene rule a CPCT/A follows on the job.
| Link | Definition | Example |
|---|---|---|
| Infectious agent | The pathogen (bacterium, virus, fungus, or parasite) capable of causing disease | MRSA, C. difficile, influenza virus |
| Reservoir | The place where the agent lives and multiplies | Human GI tract, contaminated equipment, standing water |
| Portal of exit | The route the agent uses to leave the reservoir | Respiratory secretions, blood, stool, a draining wound |
| Mode of transmission | How the agent travels to a new host | Contact, droplet, airborne, vehicle (contaminated food/water), vector |
| Portal of entry | The route the agent uses to enter a new host | Mucous membranes, non-intact skin, IV lines, urinary catheters |
| Susceptible host | A person whose defenses cannot resist the agent | Immunocompromised, elderly, post-surgical, or device-dependent patients |
Hand hygiene interrupts the mode-of-transmission link; PPE interrupts the portal-of-exit and portal-of-entry links; prompt catheter or IV removal reduces susceptible-host risk. Understanding the chain lets a CPCT/A reason through why a precaution exists rather than memorizing it in isolation.
Standard Precautions
Standard precautions apply to the care of every patient, every time, regardless of diagnosis or presumed infection status, because any patient may carry an unrecognized pathogen. Standard precautions assume that blood, body fluids, secretions, excretions (other than sweat), and non-intact skin or mucous membranes from any patient could be infectious, which is why the CPCT/A applies them universally rather than reserving them for patients with a known diagnosis. Standard precautions include:
- Hand hygiene before and after every patient contact
- Gloves when contact with blood, body fluids, mucous membranes, or non-intact skin is anticipated
- Mask, eye protection, or a face shield when splashes or sprays are likely
- Gown when clothing contact with blood or body fluids is likely
- Safe injection practices (one needle, one syringe, one time)
- Respiratory hygiene and cough etiquette
- Safe handling of contaminated equipment and linen
Transmission-Based Precautions
When standard precautions alone are not enough to stop a known or suspected pathogen, transmission-based precautions are added on top of standard precautions. There are three categories:
| Category | Spread mechanism | Example organisms | Added PPE |
|---|---|---|---|
| Contact | Direct or indirect skin/surface contact | MRSA, C. difficile, VRE (vancomycin-resistant enterococcus) | Gown and gloves before room entry |
| Droplet | Large respiratory droplets over short distances (coughing, sneezing, talking) | Influenza, pertussis (whooping cough), bacterial meningitis | Surgical mask before room entry |
| Airborne | Small droplet nuclei that stay suspended in air and travel farther | Tuberculosis (TB), measles, varicella (chickenpox) | Fit-tested N95 (or higher) respirator; patient placed in a negative-pressure airborne infection isolation room (AIIR) with the door closed |
A patient can be on more than one category at once — for example, a patient with suspected TB may also need contact precautions for a draining wound.
PPE Donning and Doffing Order
Putting equipment on and taking it off in the correct sequence is what actually prevents self-contamination, making this one of the highest-yield facts on the exam.
Donning (putting on), in order:
- Gown
- Mask or respirator
- Goggles or face shield
- Gloves
Doffing (taking off), in order:
- Gloves
- Goggles or face shield
- Gown
- Mask or respirator
Gloves come off first because they are the most contaminated item, and the mask or respirator comes off last (after leaving the room, for airborne precautions) because it protects the respiratory tract until the technician has fully exited the contaminated environment. Perform hand hygiene immediately after removing all PPE.
Hand Hygiene and C. difficile
Alcohol-based hand sanitizer is effective against most organisms encountered in patient care, but it does not kill C. difficile spores. After caring for a patient with known or suspected C. diff, the CPCT/A must wash hands with soap and water — the friction and rinsing physically remove spores that alcohol cannot destroy.
Healthcare-Associated Infections (HAIs)
HAIs are infections a patient acquires during care that were not present or incubating at admission. High-yield HAIs for the exam:
- CAUTI (catheter-associated urinary tract infection): linked to indwelling urinary catheters; prevented by using catheters only when medically necessary and removing them as soon as possible
- CLABSI (central line-associated bloodstream infection): linked to central venous catheters; prevented by sterile insertion technique and scrubbing the hub before each access
- MRSA (methicillin-resistant Staphylococcus aureus): a contact-precaution organism spread by direct contact or contaminated surfaces
- C. difficile: a spore-forming, contact-precaution organism associated with antibiotic use; requires soap-and-water hand hygiene and bleach-based environmental disinfection
CAUTI and CLABSI are both device-associated infections, meaning the risk exists only as long as the invasive device (catheter or line) stays in place — this is why daily assessment of whether a device is still necessary, and prompt removal once it is not, is one of the most effective HAI-prevention actions a CPCT/A can support. Facilities track HAI rates closely because they are a top patient-safety priority for accrediting bodies such as the Joint Commission, and they are largely preventable through the basics covered in this section: hand hygiene, correctly selected precautions, properly sequenced PPE, and minimizing invasive-device dwell time.
Consistent hand hygiene, prompt device removal, and correctly applied precautions are the CPCT/A's primary tools for interrupting the chain of infection and preventing HAIs.
When donning personal protective equipment (PPE) before entering a contact-precautions room, which item should be put on FIRST?
A patient has active pulmonary tuberculosis. Which precaution category applies, and what PPE does it require?