Intro

Question 1

What is an infection

Answer 1

What is an infection?
• Invasion of a host’s tissues by micro-organisms
&
• Disease caused by:
– microbial multiplication
– toxins - can be associated with production of toxins released into tissue asa normal aspect of microbial multiplication or dying
– host response - Diseases caused by pathogenic interaction between host and organism - disease also determined by host response - consequence of host response

Question 2

How do people get infections?

Answer 2

Majority cause by patients own microbiota going from place where they are not causing a problem to somewhere where they are
Eg streptococcus plneumoniae in throat - causes pneumonia in lungs - if aspirated eg if comatose

Question 3

What are microbiota?

Answer 3

• Microbiota = “commensals”
– micro-organisms carried on skin and mucosal surfaces
– normally harmless or even beneficial
– transfer to other sites can be harmful

Commensals implies “harmless”
Organisms vary from place to place depending on heat, humidity, etc
Normally harmless but transfer to other sites can be harmful
Eg E. coli from rectum to urinary tract can cause UTI
Difference in women and men due to anatomical differences

Question 4

What are different ways infections can be transmitted?

Answer 4

Contact and intermediary may be necked or colonised
• Physical contact required for some infections, e.g. sexually transmitted infections
• Airborne spread may be sufficient for other infections, e.g. chickenpox
• Vector may be necessary, e.g. mosquito for malaria
• Transmission due to ingestion of contaminated food or water
• Inhalation of air contaminated by environmental organisms
• Contact with contaminated surfaces, including medical devices

Question 5

What is horizonat and vertical transmission?

Answer 5

Modes of horizontal transmission
– Contact
• direct - eg salmonella when contamination of raw/cooked meat
• indirect - eg legionella in shower
• vectors 
– Inhalation
• droplets 
• aerosols
– Ingestion (faecal-oral transmission)

• Vertical transmission
– mother to child, before or at birth eg HIV via breast milk

Question 6

What are the steps that microorganisms cause disease?

Answer 6

Expose - Exposure to cell on surface of tract
Adherence
Invasion 
Multiplication
Dissemination 

At the same time may produce vilurence factors - produce by organisms and released into environment -
PVL produced by staph, aureus
PVL break down white cells - allows bacteria to reproduce quickly
Some organisms produce enzymes which have targets
Endotoxins

Question 7

What are virulence factors

Answer 7

Virulence factors 
• Exotoxins
• cytolytic
• AB toxins
• superantigens
• enzymes 
• Endotoxins

host cellular damage
• direct
• consequent to host immune response

Question 8

In which case may the host immune response be dampened down?

Answer 8

Bacteria die - causing host imflammatory response
Cellular damage consequence of damage by bacteria or host immune response
Eg meningitis
Brain cant cope with swelling
Meningitis - host response
Steroids given to damp down host response
Normally a bad thing bc limit host response to infection
But when disease process primarily caused by host immune response, damp down the response also tract with antibiotics

Question 9

What are disease determinants?

Answer 9

• Pathogen
– virulence factors
– inoculum size
– antimicrobial resistance 
• Patient
– site of infection 
– co-morbidities

Interaction between patient and pathogen
Tend to be more ill if larger innoculus
If you wasted time with ineffective agent - natural history of untreated disease
Management of “red flag sepsis” - invasion of blood stream by pathogen from Urinary tract
Every hour delay in effective antibiotic - 4-7% increase in mortality
A lot of E. coli resistant to a lot of antibiolotics
80-90% effective of 100% effective
Broad spec high guarantee to be effective but drive the resistance

Looking at whole population - patients who are diabetic - more susceptible to E. coli blood infection
Knock on consequence

Question 10

How do we know patients have an infection? What are question to answer?

Answer 10

Questions to answer 
• Is there an infection? 
• Where is the infection? 
• What is the cause of the infection? 
• What is the best treatment?

• history
– symptoms
• focal, systemic
• severity
• duration 
– potential exposures
• examination
– organ dysfunctions 
• investigations
– specific
– supportive

Question 11

What are supportive investigations to determine if a patient has an infection?

Answer 11

• Supportive investigations
– Full blood count
– neutrophils, lymphocytes
– C reactive protein (CRP) - produced during inflammation
– blood chemistry – liver and kidney function tests
– imaging – x-ray, ultrasound, magnetic resonance imaging (MRI) – histopathology

Question 12

How do we know patients have infections in terms of bacteriology?

Answer 12

• Bacteriology
– Specimen types
• swabs, fluids, tissues 
– “M,C&S”
• microscopy
– bacterial cells (e.g.Gram stain) 
– patient cells e.g. cerebrospinal fluid (CSF)
• culture 
• antibiotic susceptibility
– Antigen detection
– Nucleic acid detection

Question 13

How do we know patients have infections in terms of virology?

Answer 13

• Virology
– antigen detection (the virus)
– antibody detection (the patient’s response)
– detecting viral nucleic acid (DNA or RNA)

Question 14

Who is involved in managing infections?

Answer 14

• All clinicians encounter patients with infections
• Specialties whose primary interest is infection:
– infectious diseases
– medical microbiology and virology
– genitourinary medicine
– health protection

Question 15

What are important topics in infection?

Answer 15

• new pathogens
• antimicrobial resistance
• healthcare infections
• re-labelling of established diseases as infections