The Chain of Infection

The chain of infection is the model used to understand how infections spread. It consists of six links — all must be present for infection to occur. Breaking any single link prevents transmission.

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The Six Links

1. Infectious Agent (Causative Organism)

The microorganism capable of causing disease:

• Bacteria, viruses, fungi, parasites, prions
• The agent's virulence (ability to cause disease), pathogenicity, and infective dose determine severity
• CS role: Eliminate or reduce the infectious agent through cleaning, disinfection, and sterilization

2. Reservoir (Where the Agent Lives)

The habitat where the organism survives and multiplies:

• Human reservoirs: Patients, healthcare workers (especially carriers)
• Environmental reservoirs: Contaminated surfaces, water, equipment
• Instrument reservoirs: Biofilm in lumens, hinges, and crevices of improperly cleaned instruments
• CS role: Prevent instruments from becoming reservoirs by thorough cleaning and sterilization

3. Portal of Exit (How the Agent Leaves the Reservoir)

The pathway by which the organism leaves its reservoir:

• Blood, body fluids, respiratory secretions, wound drainage, feces
• During surgery: blood and tissue directly contact instruments
• CS role: Handle soiled instruments as potentially infectious (Standard Precautions)

4. Mode of Transmission (How the Agent Travels)

The mechanism by which the organism is transferred:

5. Portal of Entry (How the Agent Enters the New Host)

The pathway by which the organism enters a susceptible person:

• Surgical incisions (break in skin)
• Mucous membranes
• Respiratory tract
• Urinary tract
• Intravenous sites
• CS role: Ensure sterility of items that will enter sterile body sites

6. Susceptible Host (The Person Who Gets Infected)

A person whose immune defenses are inadequate:

• Surgical patients (broken skin barrier)
• Immunocompromised patients
• Elderly patients
• Neonates
• Patients on immunosuppressive therapy
• CS role: Recognize that EVERY patient is potentially susceptible

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How CS Technicians Break the Chain

Central Service professionals primarily break the chain at three points:

1. Infectious Agent — Destroy microorganisms through cleaning, disinfection, and sterilization
2. Reservoir — Prevent instruments from harboring microorganisms through thorough cleaning
3. Mode of Transmission — Prevent indirect contact transmission by ensuring instruments are sterile when they reach the patient

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Healthcare-Associated Infections (HAIs)

HAIs are infections patients acquire during the course of receiving healthcare treatment:

• Approximately 1 in 31 hospital patients has at least one HAI on any given day
• The CDC estimates 1.7 million HAIs occur annually in U.S. hospitals
• HAIs result in approximately 99,000 deaths per year in the U.S.
• Common types: surgical site infections (SSIs), catheter-associated urinary tract infections (CAUTIs), central line-associated bloodstream infections (CLABSIs), ventilator-associated pneumonia (VAP)

The work of Central Service directly impacts HAI rates. Improperly processed instruments can lead to surgical site infections, one of the most preventable types of HAIs.

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Standard Precautions

Standard Precautions (formerly Universal Precautions) treat all blood and body fluids as potentially infectious, regardless of the patient's known infection status.

In Central Service, Standard Precautions mean:

• Always wear appropriate PPE when handling soiled instruments
• Treat every instrument as if it were contaminated with bloodborne pathogens
• Never assume an instrument is safe to handle without PPE based on the procedure it was used in
• Follow the same rigorous cleaning and sterilization process for every item, every time