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
what is the tx regimen for LTBI?
- isoniazid 5mg/kg PO daily (max 300mg PO daily) for 9 months
- preferred regimen, esp in pregnancy, lactation, HIC
- co admin with pyridoxine to minimize neuropathy - rifampicin 10mg/kg daily (maz 600mg PO daily) for 4 months
- alt in pt who cannot tolerate isoniazid
benefits of treating active tb
benefit to pt
- reduce number of replicating and persisting bacteria
- achieve durable cure and prevent releapse
- prevent dev of resistance
benefit to community
- minimise transmission to others
what is the singapore tb elimination prog? (STEP)
it promotes directly observed therapy (pt come back to hospital daily to inject med, must be performed by trained personnel), dose contact investigations
national treatment surveillance regsitry
if someone has tb, need to report to MOH
what ab to use for active tb tx?
Rifampicin 10mg./kg daily, max 600mg per dose (tab: 100, 300mg)
isoniazid 5mg/kg daily (tab: 150, 300mg)
pyrazinamide (15-30mg/kg daily), max 2g (taB: 500mg)
ethambutol (15-25mg/kg daily), max 1600mg per dose (tab: 100, 400mg)
streptomycin 10-15mg/kg daily ( 1g vials)
what is the tx duration ?
standard 6 months
- 2 months intensive phase: daily admin of RIPE/S
- 4 months continuation phase: daily 3x/week admin of R and I
can only change from intensive to continuation phsae if
- confirmed susceptibility to RIF and INH or
- culture neg pulm tb
who likelty cannot tolerate PZA? what is the tx duration then?
- elderly, liver disease (PZA causes severe hepatotoxicity)
give 9months therpay
intensive 2 months RIE
continuation pahse 7 months daily or 3x/week RI
how is RIPE administered?
- TB med exhibit conc dep killing
- admin once daily
- all med taken at same time
which drugs cause hepatotox?
RIP
what are the risk factors for hepatotox SE?
age >35, female, underlying liver disease, concurrent alcohol use, HIV
how to manage if hepatotox dev in active tb:
- stop tx immediately
- monitor LFT
- re-challeng sequentially when LFT normalised and sx resolved
- if rechallenge regimen fails, may need non-heptox regimen eg. EMB+ FQ+ STM
SE of EMB?
- cause visual tox
reduced visual acuity
reduced red-green color discrimintation
how to monitor visual acuity and color dis test?
- once at baseline for all pt
- monthly monitoring in pt with any risk factors: taking taking doses > 25mg/kg, taking EMB for more than 2 months, has renal insuf eg. CKD
- educate all pt to stop tb tx and see a doctor immediately if experience change in vision
