tb Flashcards
how is mycobacterium tb transmitted?
98% airborne
access lower airways
- consumed by macrophage–> no infection
- rep in lungs–> cellular immunity
2 types
- asymptomatic (latent)
- symptomatic (active)- bac rep out of hand
what are the risk factors for latent tb? (4)
- living in urban area
- residents of prisons, homeless shelters, nursing home
- close contact with pulm tb pt
- co-infection with HIV (immunosup due to HIV, higher exposure to tb, may predispose to convert latent–> active)
what are the risk factors for active tb? (9)
- living in urban area
- residents of prisons, homeless shelters, nursing home
- close contact with pulm tb pt
- co-infection with HIV (immunosup due to HIV, higher exposure to tb, may predispose to convert latent–> active)
- children <2yo
- elderly >65
malnutrition - immunosup
what is extrapulmn tb?
eg. bone and joint, cns, spine
- mostly same tx but longer duration of tx and adjunctive therapy may be req
s/sx of tb? (5)
- fever
- weight loss
- fatugue
- productive cough
- night sweat
hemoptysis (cough out blood)
how to differentiate between pneumonia and tb?
by duration of sx
- tb: gradual onset, over weeks- months
- pneumonia: acute onset, hours or days, get very sick very quickly
what are the radiological findings for tb?
- infiltrates in apical region
- cavitary lesions
what are the indications for latent tb infection (LTBI) screening?
intent to treat if positive AND
high risk group
- children with recent tb contact
- HIV infected indv
- pt considered for tumour necrosis factor antagonist therapy
- dialysis pt- chronic disease, immunosup, access to healthcare setting, more exposure
- transplant pt
what diagnositic tests can be done for latent tb? (3)
- latent tb infection screening LTBI
- tuberculin skin test eg. Mantoux test
- interferon gamma release assay
what is the procedure for tuberculin skin test?
- inject 0.1ml of PPD intradermally
- read after 48-72h by trained reader
- read diameter of induration (not area of redness)
strenghts (3) and limitations (4) of tuberculin skin test?
+: high sensitivty (95-98%)
+: low cost
+: no need to collect blood sample
+: specific to tb (less cross reactivity)
- :false neg- immunosup
- : false pos- envr contact with non-tb mycobacteria, BCG vaccination
- : no universally accepted standard for interpreting rsults
- : inter-reader variability
what is the procedure for interferon gamma release assay?
- blood collection into special tubes
- measre interferon famma released by WBC in response to incubation with M.tb specific antigens
strengths (4) and limitations (3) of interferon gamma release assay?
+:performance as good as PPD
+: no false pos in BCG vaccinated indv
+: minimal cross reactivity with non-tb mycobacteria
+: results avail within few hours
- : more expensive
- : need for blood sample
- : false neg- immunosup
what are some infection control consideratiosn for active tb?
- in hospital: need airborne precaution (eg. neg pressure room, PPE, gowns)
- tx decreases infectiousness (generally, airborne precautions no longer needed after 2 weeks of effective tx)
- in community: no need to avoid household members (take tb med, practice cough etiquette, ventilate homes)
why treat LTBI?
- reduce lifetime risk of progression to active tb from 10% to 1%
- prior to initiation: exclude active tb (look at sx), weigh risk vs benefit
- monotherpay is adequate
