pathophysiology of TB
98% transmission via airborne
- consumed by macrophages
- replicates in lungs causing cellular immunity
latent and active TB risk factors
- residents of prison, homeless shelter, nursing homes
- close contact with pulmonary tuberculosis patients
- co-infection with HIV
Active TB risk factor
- children <2yo
- elderly >65yo
- malnutrition
- immunosuppression
- co-infection with HIV
Clinical presentation of TB
- primarily a pulmonary infection
- extra- pulmonary TB possible: in the bone & joint, spine, CNS
signs and symptoms of TB
- productive cough
- hemoptysis
- fever
- fatigue
- night sweats
- weight loss
radiological findings in TB
- infiltrate apical region
2. cavity lesions
how are TB symptoms different from pneumonia symptoms
TB: gradual onset (weeks to months)
Pneumonia: acute onset (hours to days)
indication for latent TB infection LTBI screening
- high risk group and
2. intent to treat if possible
definition of high risk Latent TB group
- children with recent TB contact
- HIV infected individuals
- pt considered for tumor necrosis factor antagonist therapy
- transplant pt
- dialysis pt
reasons not to treat TB
if patient has life limiting diseases like end stage cancer, it doesnt make sense to expose pt to more medication and toxicity
diagnostic test for latent TB
- tuberculin skin test (mantoux test, tuberculin purified protein derivative PPD test)
- interferon-gamma release assay (quantiFERON-TB- gold, T-SPOT.TB)
describe tuberculin skin test
- infect 0.1ml of PPD intradermally
- read after 48-72h by trained reader
- read diameter of induration (not area of redness)
describe interferon-gamma release assay
- blood collection into special tubes
- measures the interferon-gamma released by WBC in the response to incubation with M.tuberculosis- specific antigens
note: previously exposed to TB will be able to mount an immune response against the test
strengths of tuberculin skin test
- highly sensitive (95-98%)
- low cost
- no need to collect blood samples
limitation of tuberculin skin test
- false neg (immuno)
- false pos (environmental contact with non-TB mycobacteria, BCG vax (mostly pos >10mm)
- no universally accepted standard for interpreting results
- inter-reader variability
strengths of interferon-gamma release assay
- performance as good as PPD
- no false positive in BCG-vax
- minimal cross reactivity with non-TB mycobacteria
- results avail within few hours
limitations of interferon-gamma release assay
- more expensive
- need blood samples
- false neg (immuno- may not mount adequate immune response)
Active TB diagnosis
sputum obtained for Ziehl-Neelsen stain for acid fast bacilli AFB
- if pos, intiate tx
infection control for active TB in hospitals
- need airborne precaution
- negative pressure rooms
- PPE and N95 mask
infection control for active TB in community
- no need to avoid household members
- take TB meds
- practice cough etiquette
- ventilate homes
why treat LTBI
- reduce lifetime risk of progression to active TB from 10% to 1&
- reducing number of replicating and persisting bacteria
- achieve durable cure and prevent relapse
- prevents development of res
- minimise transmission
what to do before starting LTBI tx
- exclude active TB
2. weigh risk benefits
tx of LTBI
- isoniazid: 5mg/kg PO OD (max 300mg) x 6mth (9mth if HIV)
- co-adminster with pyridoxine (at least 10mg/d to minimise neuropathy) - rifampicin: 10mg/kg PO OD (max 600mg) x 4mth
- alternative for iso - isoniazid + rifampicin: 900mg PO weekly (300+600mg) x12w
- given under direct observed therapy
- not suitable for HIV pt
rifampicin first line TB dosing
- PO 10mg/kg OD; max 600mg
- PO 10mg/kg 3x/week; max 600mg
- no renal dose adjustment
- tablet size: 100mg, 300mg
