Principles of Disease and Epidemiology Study Notes

Infection vs. Disease

• Infection: Entry and multiplication of pathogens.

• Disease: Host's response to infection, resulting in symptoms.

Microbiota

• Normal Microbiota: Permanent residents of the host.

• Transient Microbiota: Temporarily present in host.

Relationships

• Commensal: One benefits, other unaffected.

• Mutualistic: Both benefit.

• Parasitic: One benefits at the expense of the other.

Koch's Postulates

• Purpose: To determine the causative agent of a disease.

• Four criteria:

  • Microbe present in diseased individuals.

  • Microbe isolated and cultured.

  • Microbe causes disease in healthy host.

  • Microbe re-isolated from experimentally infected host.

• Limitations: Not applicable to all diseases (e.g., polymicrobial infections).

Herd Immunity

• Definition: Immunity of a population to protect individuals.

• Mechanism: Reduced spread of disease through majority being immune.

Disease Susceptibility

• Predisposing factors: Genetics, age, lifestyle, etc.

Reservoirs and Disease Transmission

• Reservoir: Natural habitat of a pathogen.

• Transmission methods:

  • Direct contact.

  • Indirect contact.

  • Airborne.

Healthcare-Associated Infections (HAIs)

• Definition: Infections acquired in healthcare settings.

• Contributing factors:

  • Compromised host.

  • Pathogen presence.

  • Chain of transmission.

Emerging Infectious Diseases

• Definition: New or previously unrecognized infections.

• Contributing factors: Globalization, environmental changes, etc.

Role of CDC

• Purpose: To monitor and prevent disease outbreaks.

Epidemiology

• Contribution: Studies incidence, spread, and prevention of diseases.