Making an Infection Diagnosis Flashcards
What does microbiology do ?
Identify the infecting organism
Susceptibility testing
Identify clustered organisms over-represented in the community.
Diagnostic advice
Identify the infecting organism
Treatment advice
Susceptibility testing
Infection control
Identify clustered organisms over-represented in the community.
What are laboratory results for ?
- Act as a doctors back up
- Alert us to patients where the clinicians suspect infection but have not bothered to contact
- Help out when antibiotics are unpredictable
- Permit collection of alert organisms and detection of outbreak samples
- Provide an intelligence system
Why don’t clinicians use microbiology results ?
The speed of progression of infection is much
faster than the time taken to generate results
(we are too slow)
They do not understand the implications of
the data.
Describe some roles of clinical microbiologist
To provide :
- high quality diagnostic tests
- a clinical consultation service for patients with suspected infection
- clinical advice on the interpretation of diagnostic tests
- advice on therapy of serious infections
Describe the process of a diagnosis
Patient doctor interaction
Differential diagnosis
Clinical specimens
Results - refinement of differential diagnosis
Diagnosis
Therapy
How to make a microbiological diagnosis ?
Direct examination
Culture
Serology
Molecular
What is serology ?
To check for the presence or level of specific antibodies in the blood.
Types of Microscopy
Light
Fluorescent
Electron microscopy
Types of light microscopy
Direct
Gram
Z-N
Giemsa
Direct light microscopy
stool - parastites
Gram light microscopy
CSF - bacteria
Z-N light microscopy
sputum - TB
Giesma light microscopy
blood - malaria
What is fluorescence microscopy used for ?
Respiratory syncytial virus
RSV diagnosis
What is electron microscopy used for ?
Virus detection and identification
Culture diagnosis features
- More sensitive than smear
- Allows susceptibility testing
- Allows rapid presumptive diagnosis
- Allows detailed identification
- Rendered negative by antibiotics
Smear diagnosis description
- Rapid
- Simple to perform
- Cheap
- Not very sensitive
*Not very specific - Requires considerable expertise
MALDI-TOF description
A positive step
- Rapid identification of bacteria
- Does not provide susceptibilities
- Delayed by slow growth
- Of no value if antibiotics render cultures negative
Serological diagnosis function
- Detect high IgG concentration
- Detect rising of falling titres
- Detect IgM/IgA
- Measure avidity of binding
- Detect antigen
Name 7 examples of serological techniques
Agglutination
Precipitation
Complement fixation
Virus neutralisation
ELISA
Radioimmunoassay
Immunofluorescence
Examples of molecular techniques
DNA hybridisation.
Nucleic acid amplification testing.
- PCR
- LCR
- Automated DNA amplification
- Real time PCR
