TB and Other Mycobacteria Flashcards
Tuberculosis epidemiology:
Worldwide: 33% prevalence 9 million new cases/year 1.4 million deaths/year 3.7% MDR In the US: 4% prevalence 10,000 new cases/year 500 deaths/year 1.3% MDR
M. tuberculosis complex:
M. tuberculosis M. africanum M. bovis M. bovis-BCG strain M. cannetti
TB patholophysiology:
Small respiratory droplets containing TB land in the alveoli. There, they may be:
1) eliminated - no infection
2) cause immediate disease (primary TB)
3) survive dormant (latent TB)
4) survive dormant and then reactivate (reactivation TB)
Risk of progression from LTBI to TB:
5% in first 2 years, 10% over lifetime
If HIV+: 10% annually
High risk of TB INFECTION:
1) Close contact with those with TB
2) Foreign-born persons
3) Low income/homeless persons
4) Living/working in special settings
5) Healthcare workers who serve high-risk groups
6) Racial/ethnic minorities
7) Infants, adolescents, children
8) IV drug users
High risk of TB DISEASE:
1) HIV patients
2) Patients with diseases that increase risk of TB
3) Persons infected within the last 2 years
4) Infants/children <4 years old
5) IV drug users
Latent tuberculosis:
Inactive bacilli within the body TST is usually positive Chest x-ray usually normal Sputum sample/culture negative NO SYMPTOMS NON-INFECTIOUS
Active TB disease:
Active bacilli within the body TST is usually positive Chest x-ray usually abnormal Sputum sample/culture positive SYMPTOMS INFECTIOUS
Booster phenomenon:
Patient has latent TB for many years.
Patient undergoes TST, which appears as negative.
The initial TST “wakes up” the immune system, which leads to a subsequent positive TST.
“Two-step testing” is thus performed in certain populations.
TST Do’s and Dont’s of testing:
Don’t test: those with a previous positive TST or within 6 weeks of receiving a live vaccine
Do test: prior to immunosuppressive therapy, even if they’ve had BCG (remotely).
BCG and TST:
If BCG happens before age 2, TST false-positive in 1%
If BCG happens after age 2, TST false-positive in 20%
IGRAs (quantiferon):
Requires single patient visit to conduct test No booster phenomenon Fewer incorrect readings No effect of BCG vaccine or NTM Limited time to process blood samples
Treatment regimens for latent TB:
9 months of INH (best)
6 months of INH (acceptable)
New: 3 months of INH-RPT
Clinicians must RULE OUT active TB before treating latent TB.
Approach to TB diagnosis:
Clinical history Physical exam TST/IGRA Chest X-ray Bacteriological examination (specimen collection, acid-fast staining, nucleic acid amplification, drug susceptibility testing).
Treatment of active TB:
4 drugs for 2 months (initial phase). 2 drugs for 4 months (continuation phase).
4 drugs: Rifampin, isoniazid, pyrazinamide, ethambutol
Anti-TB drug side effects:
Rifampin: HEPATITIS, flu-like illness
Isoniazid: HEPATITIS, neuropathy
Pyrazinamide: HEPATITIS, GI, rash, myalgias
Ethambutol: Ocular toxicity (only bacteriostatic drug)
Primary vs. secondary resistance:
Primary resistance: patient ACQUIRES a resistant TB organism
Secondary resistance: patient DEVELOPS a resistant TB organism (usually due to medicine non-compliance)
Categories of resistance:
Mono-resistant: resistant to any one drug
Multidrug resistant (MDR TB): resistant to isoniazid and rifampin
Extensively drug resistant (XDR TB): resistant to isoniazid and rifampin, plus any fluoroquinolone, and at least 1 of 3 injectable second-line drugs.
Treatment for MAC:
Clarithromycin or Azithromycin, Ethambutol AND Rifampin
Tuberculosis BCG:
Most common child immunization in the world. Protects against disseminated TB and TB meningitis, but does not durably protect all adult TB in many studies. Can cause disease if given to infants with HIV.
Mycobacterium avium:
Causes disseminated disease in AIDS patients, or a smoldering lung disease with chronic cough in immunocompetent people.
Mycobacterium marinum:
Causes skin infections in people exposed to fish and aquatic environments.
Rarer disease caused by TB:
Miliary (disseminated) tuberculosis: diffuse “millet seed” appearance in multiple organs due to bacteremia.
Extrapulmonary tuberculosis: lymphatic, skeletal, genitourinary, CNS
TST positive cutoff of 5 mm:
HIV infection
TB contact
Organ transplantation
