Chain of Infection Notes

Learning Objectives

  • Define chain of infection components.

  • Identify examples in infectious diseases.

  • Explain its operation in communicable disease spread.

  • Differentiate between direct and indirect transmission.

  • Describe each link's role in transmission.

Infection

  • Invasion of pathogens producing disease.

  • Microorganism reproduction in tissue causing clinical response.

Infection Control

  • Practices preventing microorganism spread.

  • Protects clients/providers by reducing infection sources.

The Six Links

  • Pathogen, Reservoirs, Exit, Transmission, Entry, Host

Chain of Infection Components

  • Agent (Germs): Bacteria, Viruses, Parasites

  • Reservoir: People, Animals, Food, Soil, Water

  • Portal of Exit: Mouth, Cuts, Diapering

  • Mode of Transmission: Contact, Droplets

  • Portal of Entry: Mouth, Cuts, Eyes

  • Susceptible Host: Babies, Children, Elderly, Immunocompromised

Infectious Agent

  • Microorganism causing disease.

  • First link in chain of infection.

Reservoir

  • Pathogen's living/growing place.

  • Direct: Host. Indirect: Contaminated sources.

Human Reservoir

  • Person-to-person diseases: STDs, measles, respiratory pathogens.

  • CARRIERS: Transmit pathogen without symptoms.

Animal Reservoir

  • Diseases transmitted from animals to humans.

  • Zoonosis: Animal to human transmission.

Environmental Reservoirs

  • Plants, soil, water.

  • Fungal agents in soil, Legionella in water supplies.

Place of Exit

  • Pathogen escape routes: Mouth, Nose, Broken Skin

Method of Transmission

  • Directly: Body fluids. Indirectly: Intermediate hosts.

Direct Transmission

  • Contact: Skin, kissing, sex.

  • Droplet spread: Sneezing, coughing.

Indirect Transmission

  • Airborne: Dust, droplet nuclei.

  • Vehicles: Food, water, fomites.

Port of Entry

  • Entry routes: Broken skin, Mouth, Nose, Eyes, Genitals, Insect bite

Susceptible Host

  • Little resistance to pathogen.

  • Carriers spread unknowingly.

Kill Pathogen

  • Stop spread: Antibiotics, hand washing.

Prevent Contact

  • No escape: Quarantine/isolate.

Prevent Escape

  • Cover mouth, bandage wounds.

5 Steps of Infection Prevention

  1. Stop at source

  2. Block exit

  3. Interrupt transport

  4. Protect entry

  5. Increase defenses

Prevent Transmission

  • Stop spread: Control animals/insects, treat sewage, chlorinate water.

Block the Entry

  • No entry: Cover wounds, avoid questionable food.

Resistant Host

  • Strong immune system: Exercise, diet, vaccines.