Tb Flashcards
Features of mycobacterium
Intracellular bacteria slow growth rate Growth increases with oxygen waxy cell wall weakly gram positive identified with ziehl nielsen stain
Spread of tuberculosis
via pulmonary route
inhalation of small of droplets
Pathophysiology of tuberculosis
taken up by macrophages which can’t break it down
bacteria replicate inside cell
formation of granuloma
cell mediated response occurs at 2-8 weeks
Immune factors important for containing Tb
T cells
TNF alpha
INF gamma
What is a ghon complex?
Parenchymal granuloma and hilar lymphadenopathy
Radiological features of primary tb
bilateral hilar lymphadenopathy
middle and lower lobes affected
Manifestations of miliary tb
pulmonary - dyspnoea, cough, CP fever, night sweats enlarged LN bone/joint GI involvement CNS signs
Mortality of miliary tb
20%
Features of reactivation Tb
insidious onset of weight loss, fever, night sweats, chest pain, cough
CXR - fibrocavity changes in upper lobes
Common sites of extrapulmonary Tb
lymph nodes - 40%
pleura - 20%
GU/skeletal/cerebral - rarer
Tests for latent Tb
mantoux
Quantiferon
Limitations of mantoux test
false negative in immunosuppressed and overwhelming Tb as relies on cell mediated immunity
false positives in non tuberculous mycobacteria and BCG vaccine
What does an IGRA (quantiferon) measure?
T cell release of interferon gamma in response to stimulation by highly specific Tb antigens
Limitations of quantiferon test
less reliable in HIV when CD4 count less than 100
* not affected by non tuberculous mycobacteria or BCG
Diagnosis of active Tb
Don’t use quantiferon or mantoux in actuve disease
Visualisation of acid fast bacilli under microscopy (provides measure of infectivity)
Culture is gold standard (slow to grow 10-14 days)
Nucleic acid amplication - rapid test + provides information on rifampicin resistance
Issues in treating latent tb
dont test unless will treat
5% latent tb becomes active in first 18 months
then 5% lifetime risk of reactivation
risk of isoniazid hepatitis increases with age – therefore need to balance risk with benefit
Groups who should have screening for latent Tb
High risk of reactivation
- HIV, transplant, chemotherapy, lymphoma, leukaemia, silicosis, renal dialysis, TNF-a
Increased risk of new infection
- close contact of active tb individual
- healthcare workers with high exposure
Treatment of latent Tb
treatment decreases risk of active Tb by 90%
isoniazid for 9 months
make sure to exclude active disease with symptoms and CXR
Treatment of active Tb
Always treat with more than two drugs
RIPE for 2 months, followed by rifampicin and isoniazid for 4 months (total 6 months)
Risk factors for relapse of active Tb
Cavitation
Extensive disease
Immunosuppression
Positive sputum culture after 8 weeks of treatment
Monitoring of treatment
Sputum - average time to smear negative 3-4 weeks
Bloods for monitoring toxicity
Adherence with DOT
Rifampicin ADRs
GI upset rash Thrombocytopenia Haemolytic anaemia Colours body fluids red/orange Small risk of hepatitis
ADRs of isoniazid
Peripheral neuropathy - can be reduce with pyridoxine administration
Hepatitis (can be severe, increases with age and underlying liver conditions)
GI upset
Rash
Seizures
What is an important side effect of ethambutol
Optic neuropathy
Red green colour blindness
What predicts MDR strain of Tb
Rifampicin resistance
What is definition of MDR Tb
Resistant to both isoniazid and rifampicin
What is definition of XDR tb
Resistant to isoniazid, rifampicin, fluoroquinolone and an injectable agent
BCG vaccination
Given to infants in endemic Tb countries
Efficacy 50%
Prevents disseminated disease and meningitis in children
Live vaccine
Risk of reactivation of TB in HIV patients
5-10% per year
Effect of TB on HIV
Increases HIV replication
Accelerates progression of HIV
What is IRIS?
paradoxical worsening of Tb due to increased effectiveness of immune system
occurs 1-3 months after commencement of ART
more common if lower CD4 count and extrapulmonary disease
Treatment of IRIS
Steroids and symptomatic treatment
To prevent IRIS - initiate ART 4-8 weeks after Tb treatment
