Making an Infection Diagnosis Flashcards
What would be some reasons clinicians wouldn’t use lab results
the speed of progression of infections is much faster than the time taken to generate results
thye do not understand the implications of the data
give me some roles of microbiologist
- provide a clinical consultation service for patients with suspected infection
- clinical advice on the interpretation of results
- advice on therapy
What is the usual circle of events
Patient doctor interaction - differential diagnosis
- clinical specimens
- results
- informed diagnosis
- therapy
What processes can be performed to make such a diagnosis
Direct examination (of sample)
culture
serology
molecular
Advantages of smear diagnosis
- rapid
- simple to perform
- cheap
disadvantages of smear diagnosis
not very sensitive
not very specific
requires considerable expertise
What are the different forms of Light microscopy
Direct (stool-parasites)
Gram (CSF-bacteria)
Z-N (sputum-TB)
Giemsa (blood-malaria)
what can fluorescent microscopy used to diagnose
Respiratory syncytial virus (RSV)
What can electron microscopy be used for
virus detection and indeitification
advantages of culture diagnosis
more sensitive than smear
allows susceptibility testing
allows rapid presumptive diagnosis
allows detailed identification
Disadvantages of culture diagnosis
rendered negative by antibiotics
What is MALDI-TOF used for (advantages)
rapid identification of bacteria
Disadvantages of MALDI-TOF
Does not provide susceptibilities
delayed by slow growth
no value if presence of antibiotics render culture negative
What can serological diagnosis detect
high IgE conc rising of falling titres IgM/IgA Measure avidity (strength) of binding antigen
List me some examples of serological techniques
Agglutination Precipitation Complement fixation virus neutralisation ELISA RIA Immunoflurescence
Tell me the algorithm of all possible outcomes
this results from parallel IGRA and TST testing
examples of molecular techniques
DNA hybridisation nucleic acid amplification testing: -PCR -LCR -Automated DNA amplification -real time PCR
Examples of specimens which can be taken
UTI: - midstream urine WOUND: - pus or swab MENINGITIS: - CSF and blood PYREXIA UO: - blood for culture + serology PNEUMONIA: - Sputum - lavage - serology
What specimens could be collected when a single pathogen is present
throat swab (not diphtheria)
infection control screening
Mtb detection
What would you use when a few organisms are likely
CSF
STI samples
blood
What are some specimens with multiple pathogens
faeces abscess pus LRTI samples Oral swab Urine
What do we look at when finding evidence for a positive diagnosis
sensitivity
specificity
predictive value of a positive and negative test
What does sensitivity mean
the ability of a test to detect all true positives
equal to the number of positives obtained divided by the total number of positives
What does specificity mean
ability to identify the number of true negatives
equal to the number of true negatives obtained divided by the number of true negatives
How will cultures present when a patient has a virus
negative
legionella drawback
grows slowly and requires specialise medium
Mycoplasma pneumoniae drawback
requires specialist medium
Chlamydia psittaci, Chlamydophyla pneumoniae drawback
Obligate intracellular pathogen
how long does real time PCR take
approximately 2 hours
