Infection Diagnosis Flashcards
What does microbiology do?
Identify infecting organism
Susceptibility testing
Identify clusters organisms over-represented in community
Importance of identifying infecting organism I microbiology:
Diagnostic advice
Importance of susceptibility testing in microbiology:
Treatment advice
Importance of identifying clustered organisms in microbiology:
Infection and outbreak control
What are laboratory tests for?
Doctor’s back up
Help when antibiotics are unpredictable
Provide intelligence system
Detection of outbreak samples
Permit collection of alert organisms
Why do clinicians not use microbiology results?
Speed of progression much faster than time taken to generate results
Difficult to understand implications of data - very complex
Roles of clinical microbiologist:
High quality diagnostic tests
Clinical consultation service
Clinical advice
Advice on therapy of serious infections
Manage control of infection issues within hospital
How do you make a microbiological diagnosis?
Direct examination
Culture
Serology
Molecular
Advantages of a smear diagnosis:
Rapid
Simple
Cheap
Disadvantages of smear diagnosis:
Not very sensitive + specific
Requires considerable expertise
What does light microscopy involve?
Direct (parasites)
Gram stain (CSF - bacteria)
Z-N (sputum - TB)
Giemsa stain (blood - malaria)
What does fluorescent microscopy involve?
Respiratory syncytial virus (RSV) diagnosis
What does electron microscopy involve?
Virus detection and identification
Advantages of culture diagnosis:
More sensitive than spear
Susceptibility testing
Rapid
Detailed identification
Disadvantages of culture diagnosis:
Rendered negative by antibiotics - bacteria less likely to grow
Advantages of MALDI-TOF:
Rapid identification of bacteria
Disadvantages of MALDI-TOF:
Doesn’t provide susceptibilities
Delayed by slow growth - requires culture step on agar
Rendered negative by antibiotics
What does a serological diagnosis do?
Detect high IgG concentration
Detect rising of falling titres
Detect IgM/IgA
Measure avidity of binding
Detect antigen
Give examples of serological techniques:
Agglutination
Precipitation
Complement fixation
Virus neutralisation
Enzyme linked immunosorbent assay
Radioimmunoassay
Immunofluorescence
Give examples of molecular techniques:
DNA hybridisation
Nucleic acid amplification testing
What’s involved in nucleic acid amplification testing?
Polymerase chain reaction (PCR)
Ligase chain reaction
Automated DNA amplification
Real time PCR
Disadvantages of culture based diagnosis:
Many organisms don’t grow on agar
Specimens rendered negative by antibiotics
Missed diagnosis
Infection aetiology not understood
Missing prognostic information
What specimens have a single pathogen?
Throat swab
Infection control screening
Unusual infections
Mtb detection
What specimens have a few organisms?
CSF
STI samples
Blood
Which specimens have multiple pathogens?
Faeces
Abscess pus
LRTI samples
Oral swab
Urine
What is evidence of a positive diagnosis?
Sensitivity
Specificity
Predictive value of positive and negative test
What’s sensitivity?
Ability of test to detect all true positives
Equal to number of positives obtained divided by total number of positives
What’s specificity?
Ability to identify number of true negatives
Equal to number of negatives obtained divided by number of true negatives
What’s the normal flora?
Everywhere - many pathogens are colonisers
Interpretation of all microbiology results must be made in context of normal flora
