IOD Investigations of infections Flashcards
How is an infection diagnosed?
History Clinical Examination General investigations Microbiology investigations Sensitivity & Specificity All tests have false positives & false negatives Predictive values depend on prior probability / prevalence
Chain of investigation?
Which specimens, whether, when, how? Lab users’ guide – test only with consent Transport to lab Urgent? Point of Care Testing? Analysis in the lab Reporting from lab Telephone + electronic Guidance for the clinician & patient Electronic + in person If you send the test – you must check the result
microbiology investigations?
Microscopy Culture Antigen detection Nucleic acid detection Antibody detection
microbes?
Bacteria Viruses Fungi Protozoa Helminths
what do tests depend on?
The organism’s Microbiology….
Laboratory methods available
Commercial equipment
abscess investigations?
Aspirate Pus (not a swab)
Gram
Culture + Sensitivity
cultures?
Isolation, identification and sensitivities
blood agar haemolysis
zone of inhibition
MIC
endocarditis investigations?
3 x blood cultures ECHO Duke Criteria Antibody for culture negative Q fever Bartonella Valve 16s RNA
meningococcal meningitis investigations?
Microscopy CSF ?skin lesions Culture Blood, CSF, throat Nucleic acid detection Blood CSF Antigen detection CSF-PCR Antibody detection
mycobacterium testing?
ZN (auramine) on sputum / pus PCR on sputum if smear positive / CSF. Liquid culture + LJ slopes Role of IGRA being assessed. Cell mediated not antibody.
categories of labs?
1-no antigens
2-non-human pathogens-not contagious
3-danger of infection-TB or typhoid or brucellosis
4-non specifc pathogens-hard to manage
E coli investigations?
Culture stool on Sorbitol MacConkey agar
Bile salts select E coli
E coli 0157 NSF
Verotoxin gene probe
C diff investigations?
C diff-toxin-pcr, gdh-ag in stool cdt-card test for antigen
Virology pathway?
Microscopy Virus isolation (cell culture) Antigen detection Antibody detection Nucleic acid detection (NAATs e.g. PCR)
types
rotavirus herpes VZV-Vesicle fluid - PCR Viral swab – culture Serum VZIgM HSV-Vesicle fluid - PCR Viral swab – culture CSF-proteins and glucose in encaphelitis
