TB Flashcards
How is TB spread?
human to human via aerosols from coughing
T or F. Everyone that becomes infected by MTB develops disease
F. 90% do not
Describe TB
acid-fast bacillus, obligate aerobe that grows VERY slowly (thus, cultures take up to 6-8 weeks)
How does primary TB infection present?
most are asymptomatic (only evidence of infection is fibrocalcific nodules at the site of infection)
How does secondary TB infection occur?
viable organisms can remain dormant for years and reactivate
Secondary infection usually involves what part of the lungs?
apices
How does the mycolic acid of the cell wall of MTB promote infection?
Mycolic acids, glycolipids, arabinagalactans, and free lipids make the cell wall impermeable to many host systems
Virulence factors of MTB?
- cord factor
- sulfatides (surface glycolipids that inhibit phagolysosomal fusion once inside macrophages)
What does cord factor do?
inhibits macrophage maturation and induces TNF-a release (virulent strains grow in a cord-like pattern)
Where does MTB reside in the body?
inside alveolar macrophages (antibodies and complement ineffective)
What polymorphism promotes for bacteremia of MTB?
NRAMP1
When do granulomas begin to appear following TB infection?
3 weeks
How do granulomas form?
after TB enters macrophages, the macrophages produce Il-12 which activate TH1 cells to produce IFN-y, which then further activates them to produce TNF-a and cytokines that cause monocyte recruitment and caseous necrosis and containment of infection
Why are rheumatoid arthritis patients at an increased risk for TB?
because they are often treated with TNF-a antagonists, which is critical for granola formation
What are the risk factors for TB?
- crowded conditions
- malnourished
- alcoholism, poverty
- AIDS
- elderly
What diseases predispose a patient to Tb risk?
DM, Hodgkin lymphoma, CKD, immunosuppression
What is Miliary TB?
lympho-hematogenous disseminated Tb (BM, liver, spleen, etc.). Can follow primary OR secondary TB
HIV patients at high risk
What is ‘progressive’ primary TB?
Tb that produces symptoms (roughly 10%)
How does secondary TB present?
insidious onset of malaise, anorexia, low-grade fever weight loss, night sweats, SOB, purulent sputum, blood streaked sputum, and rarely pleuritic pain
What happens in progressive primary TB?
the initial infected tubercle can erode into a bronchus, spill its contents and infection then spread to other parts of the lung
What does progressive primary TB resemble?
acute bacterial pneumonia.
CXR of primary progressive TB?
- lobar consolidation
- hilar LAD
- pleural effusion
What is characteristic of military TB upon CXR?
millet seeds
What are some complications of miliary TB?
- meningitis
- Pott’s disease
- N/V, diarrhea
- hematuria, proteinuria, sterile pyuria
What is Pott’s disease?
vertebral osteomyelitis
Other complications of Miliary TB?
- pancytopenia (fom BM involvement)
- Adrenal insufficiency
- Epididymitis
- prostatitis
How is TB diagnosed?
- acid fast sputum stain
- culture (takes 3-6 weeks)
- PCR
What agar is needed to culture TB?
Lowenstein-Jensen agar (will not grow on BAP) OR
culture in liquid media (shows in 2 weeks)
When should TB treatment be initiated?
When TB is suspected, do not wait for confirmed diagnosis- start treatment
Treatment for primary/secondary TB?
-Isoniazid, Rifampin, Pyrazinimide, Ethambutol (RIPE)
Why is such long treatment regimen needed for TB?
- granuloma blocks ABX
- organism is slow growing
What is MDR TB?
resistant to INH and RIF (common in AIDs patients)
What is XDR TB?
resistance to INH, RIF, fluoroquinolone, and at least 1 other drug
How does HIV affect TB?
- increased frequency of false negative sputum smears
- absence of granulomas
- cavitation/bronchial damage less severe
How is latent Tb diagnosed?
- PPD (purified protein derivative)
- IGRA
How does a PPD work?
I.D. injection of tuberculin material which stimulates a delayed type hypersensitivity mediated by T cells (causes induration within 48-72 hrs)
What can cause a false positive PPD?
immunization with BCG or infection is a non-TB mycobacteria
How does an IGRA (Quantiferon gold Quan-TB, T-spot) work?
Patient blood cells are exposed to antigens from MTB and the amount of INF-y released is measured. (no false positive from BCG or NTM infections)
Latent Tb tests in HIV patients
False negatives can occur in both tests due to lack of immune response, called anergy
How is latent Tb treated?
INH for 9 months OR
INH and Rifapentine for 3 months
What determines a positive PPD?
risk factors
What is a positive PPD in someone with no known risk factors?
15+mm
What is a positive PPD in a homeless, IVDU, nursing home resident, recent immigrant, children under 4?
10-15mm
What is a positive PPD in a HIV, immunosuppressed, organ transplant, prior TB?
5-10mm
Do you measure the erythema or induration in a PPD?
induration!
How can TB be prevented?
- screen those with risk factors
- treat latent converters
- masks
