ADVANCED MICROBIOLOGY- infection tests Flashcards
Fever
sign of inflammation and can be a symtpm / sign of infection. 38 degrees plus is a temperature.
Symptoms: fever- burning up. Chills, sweats, night sweats and rigors.
Examination
Can be symptom specific e.g lung crackles, bony, tenderness or non-specific e.g pyreix, sweating.
History
If someone has travelled inside uk or outside uk. Occupation e.g. fishmonger, framer, vet, air steward.
Animal contact: which animal and nature of contact, Sexual history
Full blood count
Hb: not much help in infection- but anaemia of chronic disease (normocytic) can be caused by infection. White blood cell count- WCC can be raised in infection but other conditions too (poor specificity). Severe sepsis can lower WCC. Neutrophils typically raised in bacterial infection and lymphocytes raised in viral infection.
Inflammatory markers
CRP <5mg, ESR<0.5, procalcitonin, new e.g. TRAIL IL-6 and IP-10
Raised markers support diagnosis, negative markers make infection less likely.
LFTs
U & E’s
1) can indicate biliary sepsis
2) can identify severe sepsis, urinary tract infection
Lactate & Blood gases
Can help identify serve sepsis and respiratory failure. Also part of CURB 65 score to help ascertain how ill a patient is
Immunological tests
Detection of immune response to infection. Antibody detection: igM detection and seroconversion (change from negative to positive result from one test to a subsequent test). Fourfold rise in titre
Rise in concentration of antibody from one test to a subsequent test: ,“Titre” is 1/greatest dilution at which antibody is detectable i.e. if antibody is just detectable at a serum dilution of 1/64, the titre is 64
“Fourfold rise in titre” would be e.g. 2 → 32 or 4 → 64
Other immunological tests = IFN-γ release assays in tuberculosis
Serology
Serum is diluted down. Antibody testing: Confirms exposure to a specific micro-organism including cultivatable and non-organisms. Confirms exposure to a specific micro-organism, Cultivable and nun-cultivable organisms, Is restricted to patients with a detectable antibody response and Is retrospective so often too late to inform antimicrobial therapy decisions.
Culture
Isolation of viable pathogen enables: identification by immediate or further testing, Typing to establish organism relatedness and Sensitivity testing to direct antimicrobial therapy. This is not applicable to non-cultivatable micro-organisms. Needs to be done before antibiotics are started. Need to minimise contamination by staph. Patient sampling, sample handling, specimen transport, incubation at 35-37 degrees for 5-7 days then growth detection.
Uses and limitations: establishes the presence of a microorganism at a particular site and allows use of empiric and targeted antimicrobial therapy. But it takes lots of time.
Direct detection
Of whole organism: microscopy.
Of component organism: antigen and nucleic acid. Detection of antigen e.g. legionella antigen detection test can be used as a point of care test. Gives rapid results at bedside but requires training.
Detection of nucleic acid: Viruses e.g. influenza or bacteria e.g. strep pneumonia or 16S PCR. If primers bind to the highly conserved parts of bacteria, you can help identify any bacteria pathogen.
Direct detection use: Establishes the presence of micro-organism at a particular site so works on cultivatable and on cultivatable. Allows the use of appropriate empiric antimicrobial therapy. Does not give any information on:
Antimicrobial susceptibility or typing. Is usually the fastest diagnostic method
Sensitivity testing
Requires viable micro-organisms usually bacteria or fungi. Basic principle: culture of micro-organism in the presence of antimicrobial agent. Work out if concentration of antimicrobial that will be available in the body is high enough to kill the micro-organism. Should be liquid or solid media.
Use is to inform decision on targets antimicrobial therapy. Initial treatment is with “empiric therapy”. Subsequent treatment is targeted.
This required isolation of micro-organism and antimicrobial susceptibility testing. The correlation between antimicrobial sensitivity and clinical response is not absolute
Microscopy
Gram staining: Chemical process that distinguishes between bacterial cell walls that retain crystal violet and those that do not, when stained and washed with acetone. Gram positive- purple. Gram negative- pink
Chest x-rays & Bone x-rays
Useful in infection diagnosis e.g. pneumonia.
Imaging
CT scans = Computerised tomography
PET scans = Positron emission tomography. Radiography active Glucose monitored
