Tuberculosis Flashcards
- Explain the epidemiology of M. tuberculosis, including trends worldwide, in the US and in Wisconsin.
TB has plagued mankind throughout history, for decades isolation in sanitoriums was a major control method
development of streptomycin and isoniazid ‘46-‘52 made outpatient treatment possible and curtailed TB in industrialized countries
resurgence 1984 due to deterioration of TB public health infrastructure, HIV/AIDS epidemic and deco of MDR orgs
Mtb is estimated to infect ⅓ of the world’s population; 2 billion effected, 9 million develop it yearly
TB kills 1.5 million people each year, mostly in SE asia, sub-Saharan Africa and Eastern Europe, immunocompromised are most at risk.
in US 15million are infected M. tb with the greatest number of TB cases occurring among foreign-born from high prevalence countries, racial or ethnic minorities and those in congregate settings
over 40% cases reported in Wisconsin occurred in Milwaukee county, 50% of cases in people born outside the US
- Describe the structure and physiology of M. tuberculosis, including virulence factors/mechanisms.
M tb produces an unusual, waxy coating on the cell surface, primarily composed of my colic acid (impermeable to usual stains; classified as acid fast because they retain carbol fuchsin stain (alt. fluorescent aura mine-rhodamine dye)
M tb is an intracellular pathogen and ingest but not killed by macrophages due to inhibition of phagolysosome fusion; its ability to multiply in macrophages is key to virulence
cord factor- surface glycolipid found only in virulent strains, triggers TH1 response and enhances survival in macrophages
- Describe the transmission of TB infection and TB disease.
reservoirs of persons with caviar lung lesions, and expelled into environment via coughing, singing or sneezing
small droplets 1-5 microns may reach alveoli where infection can begin
infection depends on # organisms expelled, ventilation and size of room, length of time exposed/ rate ventilation and immune status of the exposed person
- Explain the significance of co-infection with HIV and the mycobacteria involved.
any compromise in CMI may result in a poor outcome with active disease or disseminated disease
for most 10% lifetime risk of infection progression to disease with 50% of risk in first 2 years
disseminated/miliary TB is most common in immunocompromised (organs are seeded with millet like lesions) which is commonly seen in persons co-infected with HIV –> high mortality if not treated
high burden of co-infection in sub-Saharan Africa
HIV is the strongest risk factor for someone with latent TB to progress to active disease, w/o proper treatment 90% people living with HIV die within months of contracting TB
HIV modifies the clinical presentation of TB (radiographically atypical)
persons with HIV risk development of environmental mycobacteria, dx. with blood cultures
- Discuss why young children need to be identified soon after contact with an individual who has active disease, including predisposing factors.
children have an increased risk for developing severe disease within weeks to months of infection; are also at increased risk for TB meningitis (often results in deafness, blindness, paralysis and mental impairments)
dx. can be difficult if child is unable to produce sputum for lab tests or have extra-pulmonary TB lesions
extra pulmonary TB occurs more commonly in children
disseminated/miliary TB is common in children (organs are seeded with millet like lesions)
- Discuss the laboratory tests available to diagnose M. TB.
several stains can demonstrate acid fast bacilli: Ziehl-Neelsen, Kinyoun and Flurochrome
to detect AFB in smear 5,000-10,000 bacilli/mL needed (50-80% of patients)– positive smear presumed to be TB until proven otherwise
Nucleic acid amplification, fast but low sensitivity, neg test does not exclude TB dx.
difficult to grow and slow growing, may take 5 weeks before a M tb positive specimen can be ID’d and drug susceptibilities known by traditional techniques
- Explain the rationale of targeted tuberculin testing and why the tuberculin reaction occurs.
reason to test include find latent TB that would benefit form tx. or TB disease that should be treated
PPD should only be done in higher risk groups for exposure or disease once infected
reaction to PPD is due to type IV hypersensitivity (TH1 activation and cytokine release)
- Explain the importance of timely reporting of all TB cases (or suspected cases) to local public health departments.
all TB cases or suspected TB cases are to be reported to local health dept. within 24 hrs., delay can result in delays of treatment plan and protecting contacts
- Discuss the role of non-tuberculous mycobacteria in human disease.
aka environmental mycobacteria, or atypical mycobacteria can be acquired from environment by aspiration or inoculation and can resistance to many 1st line antituberculous agents
NTM cause more disease in WI than M tb
- Explain the concepts that are important in effective treatment of TB disease and LTBI with antimicrobials.
for DISEASE: tx. must be prolonged (6-9mo) because M tb are slowly dividing, intracellular pathogens
more than one drug used to combat resistance, monitoring for drug reactions are important, with adherence, patients are non-infectious within 2-3 weeks
LTBI: rule out TB disease, standard tx. is isoniazid for 9 mo.
- Of the 7 mycobacteria that comprise Mycobacterium tuberculosis complex which are most significant to human health ?
[M. tuberculosis, M bovis, Mafricanum, M microti, M canetti, M caprae and M. pinnipedii]
M. tb is the primary cause of TB, M bovis and M aftricanum are rare causes
- Describe the basics of how TB is spread and what serves as a reservoir of TB. How is most likely to be susceptible to TB?
humans are the only natural reservoir of M. tb
TB is spread person-to-person by aerosols
TB equally affects females and males
an increased risk of mortality exists at extremes of age
- Describe the transmission and pathogenesis of TB infection and TB disease.
circulating macrophages engulf M tb in the alveoli and bring them to regional lymph nodes accompanied by a silent bacteria
unrestrained replication proceeds both in the initial foci and metastatic foci for several weeks until concentration reaches 10^3-10^4 which can elicit the CMI response
activated T cells and macrophages surround and form granulomas, most of these granulomas heal through fibrosis and calcification. well oxygenated lesions (apical lungs) the bacilli may be walled off but remain viable –> LTBI
What is TB disease?
active or clinical disease; patient has M tb and symptoms are present
What is the action of BCG vaccination?
does not prevent infection but induces a more rapid response by alveolar macrophages and helps to prevent bacteremia (contraindicated in pregnancy and anyone with compromised immune response)
