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Flashcards in Session 1 - Introduction to Infection Deck (12)
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What is an Infection?

The invasion of a host's tissues by microorganisms.

Infections can be caused by: microbial multiplication, toxins, and the host response.




How do people get infections?


Describe patient to patient infections

Some microorganisms are carried on the skin and mucosal surfaces of our body.

These are normally harmless in their relevant areas (some even are beneficial).

If transferred to another site, they can be harmful and cause infections.

Example: E. coli in the bowel and colon being transferred to the urinary system leading to a UTI


Describe source (to intermediary) to patient infections

Physical contact is required for some infections (STIs)

Airborne infections can also occur (chickenpox)

An intermediary (vector) may sometimes be necessary for transmission (mosquitos and malaria)


Describe environment to patient infections

Transmissions can be due to contaminated food or water (cholera)

Inhalation of contaminated air by environmental organisms (chickenpox)

Contact with contaminated surfaces, including medical devices (E. coli)


What are the horizontal methods for disease transfer?

Contact - direct, indirect, vectors

Inhalation - droplets, aerosols

Ingestion - faecal-oral transmission


What are the vertical methods of disease transmission?

Mother to child (can happen either during or immediately after birth)

Can come from placenta transmission, or even through breast feeding.


How do bacteira cause disease?


How do viruses cause disease?

Viruses have to replicated within a host cell.

Viruses therefore, have to adhere to a specific cell surface structure (normally a receptor)

Viruses are then absorbed into the cell where they can then replicate within the cytoplasm.


What are virulence factors?

Virulence factors are molecules that are produced by a microorganism that help with their effectiveness in dissemination.

Examples: capsules, exotoxins, and endotoxins in bacteria


What are determinant factors and how do they affect whether or not an infection occurs?

Pathogen determinant factors:

Virulence factors, inoculum size, and antimicrobial resistance

Patient determinant factors:

Site of infection, and comorbidities (is there anything else happening to the patient, example: immunocompromised?)


What supportive investigations should you conduct when a person presents with what is likely to be an infection?

  • Full blood count: neutrophils and lymphocytes raised during infection
  • C-reactive Protein levels: acute phase protein that goes up in the inflammatory process
  • Blood chemistry: liver and kidney function tests
  • Imaging: x-ray, ultrasound, MRI, CT scan
  • Histopathology: gram staining, microscopy, culture, blood film
  • Antigen detection testing
  • PCR for nucleic acid detection (DNA for bacteria, RNA for viruses)
  • Antibiotic susceptibility: checking which antibiotics can kill them
  • Virology
    • antigen detection for the virus
    • antibody detection (the patient's response)
    • detecting viral nucleic acids (DNA or RNA)