L62 Tuberculosis Flashcards
Which of the following about tuberculosis is correct?
A. Humans are the only reservoir
B. Only pulmonary and laryngeal TB are potentially contagious
C. It is an aerobic organism
D. It is spore-forming
E. It is a non-motile bacillus
All except D
It is non-spore forming
Mycobacterium tuberculosis has high cell wall content of high molecular weight __________.
It has fast/slow growth
and it can be stained by ____________ because it is an acid-fast bacillus.
lipids;
slow growth (15-20 hours)
Ziehl Neelsen stain
What are the advantages and disadvantages of using acid-fast stain for detecting mycobacterium tuberculosis?
Adv
- simple, inexpensice
Disadv
- Low sensitivity
- Cannot distinguish between Mycobacterium tuberculosis and non-tuberculosis mycobacterium
What is the strongest risk factor for tuberculosis?
HIV
At a very young age (<5 years old), primary pulmonary tuberculosis is a progressive primary disease which does not only cause local progression to other lung areas, but also?
Prevention?
- Lympho-hematogenous dissemination: miliary-meningeal disease
- BCG vaccine for protection
At 5-12 years old, it is a relatively disease-resistant period and is usually non-progressive. Progression is usually (if any) @ (site) ?
It also occurs in puberty/young adulthood.
Extra-pulmonary/ Apical pulmonary TB
In adolescents and adults, TB can either be primary or recurrent.
Primary infection is usually without signs or symptoms. It can either be typical primary complex OR typical chronic pulmonary tuberculosis without primary complex.
Recurrent TB is usually present at (site)?
Causes what in the lungs?
Subapical-posterior position of the upper lobe. (due to high O2)
> > > Pneumonitis, cavitation, caseation of the lung
For early TB infection, patients tend to be asymptomatic.
What would TB patients present with later? (3)
- Non-specific constitutional symptoms
- LOA, LOW, fever, night sweat - Productive cough + hemoptysis
- Hemoptysis due to endobronchial erosion, massive due to artery erosion - Pleuritic chest pain if parietal pleural is involved.
What is latent infection of TB?
What risk does it cause?
- A state of the persistent immune response to stimulation of M.tuberculosis antigens without evidence of clinically manifested active TB.
- Lifetime risk of endogenous reactivation
Give the 4 examples of extra-pulmonary TB (miliary nodules can be seen in CXR).
- Laryngeal TB: hoarseness and dysphagia
- Pott disease: back pain
- Colonic TB: ulceration (GI bleed), perforation
- Anal TB: anal fistula, perirectal abscess > anal pain
If suspected TB, the first line of investigation?
Sputum for AFB
If AFB smear is positive, What to do next?
GeneXpert 1. if positive: - MTB complex - Rifampicin resistance - Await culture and susceptibility of other drugs (initiate treatment first)
- if negative
- Non TB microbacteria (high sensitivity)
- await culture for species identification
If AFB negative, what to do next?
Culture in solid/liquid medium:
MPB64: specific antigen for MTB complex
- MPB64 positive > MTB
- MPB64 negative >NTM
What is the gold standard for diagnosing TB?
Advantages and disadvantages?
Culture in Lowenstein Jensen medium (solid medium)
Adv:
- strain identification, susceptibility testing
Disadv:
- slow result, in 3-8 weeks
What are the adv and disadvantages of culture in liquid broth?
Adv:
- result in 1-3 weeks (c.f. 3-8weeks)
- strain identification, susceptibility testing
Disadv:
- Cannot quantitate growth as Lowenstein Jensen medium
Other than acid fast stain and LJ medium, what other diagnostic assays can be used for TB?
- MTB PCR
- better sensitivity than AF stain
- identify M.tuberculosis complex
- culture still needed to identify the species and susceptibility testing - PCR with GeneXpert MTB/RIF
- high sensitivity
- detects also rifampicin resistance
- culture still needed for susceptibility testing
Drug susceptibility testing for TB can be by phenotypic testing or genotyping testing which is?
Genotyping testing:
- DNA sequencing to look for genes responsible for drug resistance
Other than diagnostic assays, what further investigations can be done? (4)
- Imaging
- CXR
- 18F-FDG-PET/CT: increase uptake in regions affected by TB (extra-pulmonary TB) - Sputum induction by hypertonic saline aerosols
- Bronchoscopy + transbronchial biopsy + bronchoalveolar lavage
- Histological examination of granuloma (but may also be seen in NTM (non-tuberculosis mycobacterium) disease, or other infectious/autoimmune diseases)
What is expected to be to seen in TB CXR?
- Hilar lymphadenopathy
2. Ghon focus
What test can be done for patients with a high risk of developing TB e.g. close TB contact, HIV, etc.?
Describe the test. (3)
Tuberculin skin test (TST)
- 2TU (tuberculin units, 0.1mL
- Intradermal injection of purified protein derivative (PPD)
- Measure the size of skin induration after 48-72 hours.
What are the possible false positives and false negatives of the Tuberculin skin test?
- False positive
- NTM (non-tuberculosis mycobacterium) infection
- BCG vaccine - False negative
- HIV
- Steroids
- Malnutrition
What is Interferon-gamma release assay? (IGRA)
- Incubate the subject’s blood with TB antigens
- Measure the release of interferon-gamma
- overcome limitations of TST
limitations of TST - (false positives, operator-dependent, require follow-up visit)
TB is a notifiable disease. In presumed and confirmed TB, what preventive measures are taken by medical workers? (2)
- Negative-pressure isolation room
2. N95 masks
Drug of choice for TB?
- Rifampacin (R)
- Isoniazid (H)
- Pyrazinamide (Z)
- Ethambutol (E)
What is MDR? (Multi-drug resistance)
Patient who is resistant to both rifampicin and isoniazid.
What is XDR? (Extensive drug resistance)
Resistant to both rifampacin and isoniazid + any fluoroquinolone + at least one of the 3 SLIDS (capreomycin, kanamycin, amikacin)
If site of infection of TB is the lung, what is the treatment regimen?
2 months of HRZE + 4 months of HR
Treatment for latent TB?
- 6-9 months of isoniazid/
- 4 months of rifampicin
- 3 months of weekly rifapentine + isoniazid
Prevention of TB?
BCG vaccine
- for patient <5 years old
- 50-80% efficacy in preventing severe, extra-pulmonary TB
Why is it important to keep the Lowenstein Jensen medium jar airtight? (2)
- Mycobacterium tuberculosis is highly infective
- Prevent other organisms from contaminating the medium
What to expect to see in AFB test if the organism is mycobacterium tuberculosis?
Pink rod-shaped bacteria (bacilli)
