Reservoirs, Transmission, and HAIs

Reservoir of Infection

• A reservoir is a place that provides pathogens with adequate conditions for survival, multiplication, and opportunity for transmission.

• It can be a living organism or an inanimate object.

Types of Reservoirs

• Living Reservoir:

  • Human Carrier: An individual infected with a pathogen.

    • Asymptomatic Carrier: An individual infected with a pathogen but does not exhibit disease symptoms.

    • Passive Carrier: An individual not infected but can spread the pathogen (e.g., not washing hands).

  • Animal Vector: An animal that can spread disease to humans.

    • Biological Vector: An animal actively participating in the pathogen's life cycle (e.g., mosquitoes for Plasmodium, the malaria-causing agent).

    • Mechanical Vector: An animal not actively participating in the pathogen's life cycle (e.g., a house fly landing on feces and then on food).

  • Zoonotic Infection: An infection that can transmit from animals to humans and back to animals (zoonoses).

    • Examples: Rabies (bats, skunks, dogs), Lyme disease (mice).

• Non-living Reservoir:

  • Examples: Soil, water.

    • Clostridium tetani and Clostridium botulinum can be found in soil and animal feces used as fertilizers.

Transmission of Disease

• Once infection occurs, the disease develops.

Contact Transmission:

• Direct Transmission:

  • Also known as person-to-person transmission.

  • Prevention: Use gloves and other appropriate PPE (Personal Protective Equipment).

• Indirect Transmission:

  • Transmission through fomites (non-living objects involved in spreading infection).

  • Examples: Tissues, handkerchiefs, towels, drinking cups, eating utensils, money, toys, thermometers.

• Droplet Transmission:

  • Microbes spread through droplet nuclei that travel only short distances.

• Vertical Transmission:

  • Mother to child during pregnancy

• Biological Vector

Vehicle Transmission:

• Waterborne Transmission:

  • Untreated or poorly treated sewage often causes waterborne transmission of disease.

  • Examples: Cholera, Waterborne shigellosis

• Foodborne Transmission:

  • Pathogens transmitted in foods that are incompletely cooked, poorly refrigerated, or prepared under unsanitary conditions.

  • Examples: Food poisoning (Salmonella), tapeworm.

• Airborne Transmission:

  • The spread of pathogens by droplet nuclei that travel more than 1 meter from the reservoir to the host, such as by sneezing, coughing, and dust particles.

Vector Transmission:

• Mechanical vs. Biological transmission.

Nosocomial Infection

• Healthcare-Associated Infection (HAI): Infections patients acquire while receiving treatment for other conditions at a health facility.

• The CDC (Centers for Disease Control and Prevention) estimates that approximately 1 in 25 hospital patients has at least one HAI on any given day.

• HAIs result from a combination of several factors; any one factor alone is typically insufficient to cause infection.

Factors Contributing to HAIs

• Microorganisms in the healthcare-associated environment.

• Compromised host.

• Chain of transmission.

Common HAIs and Related Factors

• Urinary tract infections (UTIs): Often related to urinary catheterization.

• Respiratory infections: Often related to respiratory devices that aid breathing or administer medication.

• Surgical site infections & Lower respiratory infections are the most common infections in hospitals

• Other infections:

  • Urinary tract infections: 22%

  • Surgical site infections: 22%

  • Lower respiratory infections: 16%

  • Gastrointestinal infections: 13%

  • Bloodstream infections: 10%

  • Other: 17%

Predisposing Factors

• Factors that make the body more susceptible to a particular disease.

  • Gender: Females have a higher incidence of urinary tract infections.

  • Genetic background: Family history of cancer.