Infection 3 - Infection Model + Making Diagnoses

Question 1

What are the 6 stages of the infection model?

Answer 1

1) Patient
2) Pathogen
3) Mechanism of infection
4) Process of Infection
5) Patient management
6) Outcome

Question 2

What does step 1 + 2 of the infection model include?

Answer 2

Patient

1) Person - e.g.: age, gender, physiological state (e.g.: pregnancy), pathological state (e.g.: immunosuppressed) + social factors
2) Time - e.g.: calendar time (e.g.: flu season) + relative time (e.g.: incubation period)
3) Place - e.g.: current and recent travels

Pathogen - e.g.: virus/bacteria/fungi etc, all of those likely to affect what the infection does.

Question 3

What does step 3 of the infection model include?

Answer 3

Mechanism of infection

1) Contiguous (direct) spread - e.g.: skin to skin or mucous membrane.
2) Inoculation - something injected into tissues
3) Haematogenous - spread through blood stream
4) Ingestion - e.g.: contaminated food/water
5) Inhalation
6) Vector - e.g.: mosquitos
7) Vertical transmission - mother to child

Question 4

What does step 4 of the infection model include?

Answer 4

Process of infection

1) Attachment - organism has to attach itself to host cells
2) Interaction with host
3) Toxin production + inflammation - leading to host damage.

Question 5

What do steps 5+6 of the infection model include?

Answer 5

Management:

• History, examination + investigations for diagnosis
• Treatment will be specific (anti-microbials, surgery) or supportive (e.g.: paracetamol for fevers) which is symptom relief + physiological restoration. Not always possible/necessary to identify exact causative agent, diagnosis enough.

Outcome:

1) Cure (+/- disability)
2) Death

Question 6

What is the human microbiota?

Answer 6

Microbiota = “commensals”. Micro-organisms naturally carried on skin + mucosal surfaces. usually helpful/harmless. Transfer to other sites can be harmful.