TB/NTM Flashcards
What type of bacteria is Mycobacterium tuberculosis?
Acid fast bacillus (mycolic acid makes it impervious to gram staining)
What is the leading cause of infectious death
Tb
What percentage of children encounter delays in diagnosis of TB
90%
What are the three trajectories for TB infection in children?
- Immediate killing (TST/IGRA negative)
- Latent TB (TST/IGRA positive), can lead to reactivation
- Primary progressive TB
How do children often acquired Tb?
Close contact with infectious adult case
90% of children who progress to TB disease do so within ___ years of infection
1 year
What is latent Tb
Asymptomatic, well child, normal CXR, TST/IGRA positive
How does Pulmonary TB present
Fever, cough, weight loss, lethargy. 50% are still asymptomatic, found through contact tracing
Clinical presentations of TB
- Latent TB
- Pulmonary TB
- Extrapulmonary TB (TB adenitis, TB meningitis, TB percarditis, TB peritonitis, BJI)
- Miliary TB
- Congenital TB
Diagnosis of TB
- TST (Mantoux)
- Qunatiferon Gold (IGRA)
- AFB smear
- Rapid PCR
How does TST work
Intradermal injection with purified protein derivative. Read at 48 - 72 hours. Positive result = LTB or TB disease, negative test doesn’t rule out TB disease
How does IGRA work
Measures IFN-y in blood in response to TB antigens. Positive result = LTB or TB disease, negative test doesn’t rule out TB disease
What is ELI-spot/T spot
Number of peripheral mononuclear cells that make IFN-y after antigen stimulation
What is AFB smear
x3 resp samples or x3 early morning gastric aspirates (most children smear negative due to pauci-bacillary disease)
How do rapid molecular methods work
PCR. Can also detect rPOB gene which predicts rifampicin resistance. Highly specific, 98%
Classic imaging findings TB on CXR
Hilar lymphadenopathy, lobar consolidation, diffuse small nodules (milliary), RUL involvement (adolescents), pleural effusions, cavitations
TB Treatment
LTBI: 3 months RH or 6 months H
TB disease: 2 months RHZ + 4 months RH
SHINE trial
4 months treatment was non inferior to 6 months for TB disease that is non severe, smear negative and not drug resistant (2 RHZ + 2 RH)
TB drugs
R = Rifampicin
H = Isoniazid
Z = Pyrazinamide
E= Ethambutol
Disseminated TB treatment
12 months total
Adjunct to TB drugs
Steroids (if TB meningitis, airway obstruction, pericardial, milliary)
Pyridoxine to prevent Isoniazid peripheral neuropathy in breast fed babies, adolescents, malnourished child, HIV positive, peripheral neuropathy
Side effects of TB treatment
RHZ = LFT derangement
E = Optic neuritis and red green colour blindness
H = Peripheral neuritis
What is BCG vaccine made from
Mycobacterium bovis isolate, live attenuated vaccine
How effective is BCG vaccine
80% effective against severe forms (Milliary + miliary) in young infants
How does BCG affect TB diagnostic tests
Can cause false positive TST, no impact on IGRA
Side effects of BCG vaccine
Local scar, injection site abscess, regional adenopathy, osteitis, disseminated BCG disease
Where are NTM found
Soil, food water animals
Most common NTM
Mycobacterium avium intracellulare (MAIC)
Most common clinical manifestation of NTM
Lymphadenitis
What is MSMD
Mendelian Susceptbility to Mycobacterial Disease, caused by IL-12 deficiency and interferon gamma receptor defects. Occurs post HSCT, in HIV. Impaired cell mediated immunity
Spectrum of NTM infections
Cutaneous, disseminated, pulmonary (Bx, CF, PCD)
Diagnosis of NTM
Culture/PCR
TST may be positive with MAIC cervical lymphadenitis
IGRA has less cross reactivity for MAIC and most other NTM species
Types of NTM
MAIC, M. fortuitum, M. absessus, M marinarum
Treatment for MAIC adenitis
Natural history is slow resolution
1. Excision
2. I&D risks sinus and fistula formation
3. If resection not possible, consider Clarithromycin/Azithromycin + Ethambutol +/- Rifampicin
