Comorbidities Flashcards
What are the 3 diagnostic techniques used in TB?
Clinical history
Imaging - x-ray, CT
Microbiological investigations
What are examples of microbiological investigations used in TB?
Smear
Nucleic acid amplification tests
Culture
Antimicrobial susceptibilities of isolated mycobacterium tuberculosis
Why can samples for diagnosing TB be taken from many parts of the body?
TB can infect virtually anywhere, so samples received in the laboratory are varied
What are examples of sample types that can be taken to diagnose TB?
Pulmonary samples
Lymph nodes
Renal/Bladder
CSF
Biopsy or fluid aspiration from bone, joints, liver and other organs
When are pulmonary samples taken?
In cases of pulmonary TB
What are examples of pulmonary samples?
Sputum
Bronchoalveolar lavage/ washing
Pleural fluid
What are ways to obtain samples from the lymph nodes?
Lymph node dissection - excised entirely
Lymph node biopsy - fine needle aspirate
Imaging-guided biopsy
EBUS - endobronchial ultrasound biopsy of medisastinal nodes
Where are the mediastinal lymph nodes?
Center of the chest
What sample is taken from the renal/bladder?
Early morning urine samples
Why is CSF taken?
TB can cause meningitis and brain abcesses
Why are bone, joints and liver biopsies/aspirations taken?
As TB can go anywhere
M. tuberculosis is notoriously difficult to isolate and grow
TRUE or FALSE
TRUE
What are the difficulties in isolating M. tuberculosis?
Samples are often contaminated with other organisms
Some patients will not be able to produce sputum
Slow-growing organism
Samples are often paucibacillary
What happens if the patients are unable to produce sputum?
Bronchoscopy
Induced sputum
How can you induce sputum?
Inhale nebulised saline
Irritates the lung
Induces the production of sputum
How much time is needed for the M. tuberculosis to divide?
16-20 hours
What does paucibacillary mean?
Having or made up of few bacilli
Low number of organisms to start with
What type of organism is M.tuberculosis?
Hazard group 3
Which laboratory handles M. tuberculosis?
Containment level 3 laboratory
- Special airflow
- Equipment
- Filters
What does a hazard group 3 organism mean?
Has potential to cause severe disease
Poses risk to people handling it
Potential to spread to people
How is the sample prepared for investigation?
Samples received have low numbers of bacteria
Need to concentrate by centrifugation to maximise yield
Non-sterile specimens are decontaminated to lyse other organisms
What is a smear?
Small proportion of concentrated sample
How is the smear prepared to be investigated?
Sample heat-fixed to microscope slides
Stained with a fluorescent stain such as auramine-O
Decolourise with 0.5-1% acid alcohol
Examine with a fluorescent microscope at x200-400 magnification
What is the purpose of decolorising the smear with acid alcohol?
Mycobacteria have lipid-rich walls
Pick up stain and retain them
If you see a fluorescent bacteria with microscope = definitely mycobacteria
What are the advantages of fluorescent microscopy?
Easy to screen
Better sensitivity than routine microscopy
All TB patients are smear-positive
TRUE or FALSE
FALSE
Around 90% are
What indications do smear-positive smears indicate about TB?
More likely to be infectious
What is done after a smear test comes back positive?
Get patient to treatment
Make sure not pass to other people
Quantify how positive a sputum slide is
What are the two procedures in which NAAT can be used to determine the antimicrobial susceptibility of the bacteria?
Genexpert
Genotype MTBDRplus
What does Genexpert consist of?
Mini PCR laboratory inside a blue box
How is the sample added to the Genexpert machine?
Take out concentrated decontaminated sample
Put in front of machine within 24 hours
What two things does the Genexpert machine determine?
Determines whether M. tuberculosis is present
Tells us by looking at specific gene sequences if the organism is susceptible to a specific antibody
How is the sample added to the Genotype MTBDRplus machine?
Concentrated and decontaminated sample is amplified using PCR
Nitrocellulose membrane with small sections of DNA bound to it
What does Genotype MTBDRplus test for?
Look for 3 specific genes involved in antibiotic resistance
Those genes are amplified
What is the positive result for the presence of resistance genes in Genotype MTBDRplus?
Blue line
What is the gold-standard for diagnosing M.tuberculosis?
Culture
What is the main disadvantage of culture?
Slow process
Takes 8 weeks
What is a culture method used to grow TV?
Lowenstein Jensen media
Egg-based medium
Concentrated decontaminated sample is inoculated onto the medium
What is a modern culture method?
Mycobacteria growth indicator tube system
Fluorescent indicator flags when something grows in the tube
How does Mycobacteria growth indicator tube system work?
Fluorescent is bound to oxygen
As bacteria grows and divides, uses the oxygen and disassociates it from the fluorescent molecule
Sensor detects when something is growing
Analyser flags when something grows in the tube
What type of growth medium is used in the Mycobacteria growth indicator tube system?
Liquid culture
What are the advantage of Mycobacteria growth indicator tube system?
Machine reads the growth automatically
Less input from a scientist
Growth time is faster in liquid media
What is another method of detecting the presence of M. tuberculosis?
Colour indicator on bottom
CO2 produced by bacteria that divide and respire
Drops the pH of the tube
Every 10 minutes - pH is detected
The colour of the indicator changes accordingly
What proportion of TB cases are multi-drug resistant?
5% of cases
What two drugs indicate MDR-TB?
Rifampicin
Isoniazid
What if TB is only resistant to Isoniazid?
It is not considered MDR-TB
What are four ways in which patients acquire MDR-TB?
Infected with a resistant strain
Poor compliance
Poor absorption
Interactions with other drugs causing subtherapeutic levels
What is the amount of time patients with TB have to take medication?
6 months
Why may patients not comply with the drug schedule?
Side-effects may make them stop taking the drugs since they feel better
What are the two ways to detect resistance?
Phenotypically
Genotypically
Why is it important to detect resistance in the population?
Make sure the patient is on correct treatment
Make sure the drug resistant strains don’t spread
What is the phenotypic method for detecting resistance?
Isolates of M. tuberculosis are incubates in the presence of anti-TB drugs
Gives absolute definite idea whether strain is susceptible
What are the pros of phenotypic testing for detecting resistance?
Gold-standard result
Know that organism growing is categorically susceptible or resistant to antimicrobial agent
What are the cons of phenotypic testing for detecting resistance?
Takes time - weeks needed to know if the patient is on the correct treatment
Need to isolate - 1/3 of cases can’t
Need laboratory facilities
What does the genotypic testing for detecting resistance entail?
Detect mutations on genes that may confer resistance
What are the pros of genotypic testing?
Speed - hours
Can be performed on samples - no need to grow
What are the the cons of genotypic testing?
Less accurate than phenotypic methods
Many gene mutations may not cause resistance
Phenotypically can confer resistance whilst genotypically can be susceptible
What is the most sensitive method of diagnosing TB?
Culture > NAAT > smear
Why is NAAT less sensitive in diagnosing TB?
Lipid wall is very thick
Difficult to obtain the RNA
PCR not as effective
Why is it important to test for Mycobacteria TB specifically?
Over 130 species of mycobacteria
Downstream tests needed to confirm it is tuberculosis
Why is TB called the great imitator?
A lot of symptoms overlap with other diseases
What are methods of monitoring TB after diagnosis and treatment?
Smear conversion
Culture conversion
Detection of acquired resistance
What is the process of smear conversion?
Look for the reduction of bacteria in smear
Gives an idea of how the treatment is going
If the sputum that is coughed up contains less bacteria = antibiotics are effective
What is the main disadvantage of smear conversion?
Arbitrary system
Quantifying the number of bacteria is difficult
Quality of sample differs between periods of taking the samples
Not absolute
What is culture conversion?
Look for not being able to grow the bacteria in the sputum of the patient
How can we detect acquired resistance?
Need to find out why bacteria are resistant
Sensitive stains may have acquired resistance due to
- poor compliance
- poor absorption of antibiotics
How are the patients managed following TB diagnosis?
Anti-tuberculosis treatment
Clinical and microbiological improvement
What anti-tuberculosis treatment is used?
Empirical first
Modified based on drug susceptibility tests
How is clinical and microbiological improvement tested for?
Smear and culture conversion
Improvement in clinical well-being
Look for
- improvement of inflammatory markers
- weight gain
- improvement of imaging
What inflammatory markers are used to look for clinical and microbiological improvement?
White cell count
C-reactive protein levels
What is seen when patients improve in CXR?
Consolidations or cavities improve
What are other important infections in HIV?
Oral candidiasis
Mycobacterium avium
PCP
What is PCP?
Pneumocystitis jiroveci pneumonia
Fungal disease
What is oral candidiasis?
Yeast that can grow abundantly in the mouth
What is Mycobacterium avium?
Severe intestinal disease
Disseminated disease like sepsis in advanced HIV
