Latent tuberculosis infection

Prior exposure to TB leading to persistent latent tuberculosis, usually contained within lung ganulomas
Goal is to identify those who are at increased risk of developing active TB and would benefit from treatment

Investigations

Tuberculin skin test (TBST)
- Sens 90%, Spec >95
Interferon-gamma release assay (IGRA)
- Sn 95%, Sp >95%
- Preferred for those who have received BCG after infancy

Is it truly positive?
- Consider IGRA
- BCG vaccine can be considered a cause of false positive when
  - vaccine given after 12 months of age, and
  - patient has no risk factors, and
  - either Canadian-born non-Aboriginal, or not from endemic country
Rule out active TB
- signs/symptoms
- CXR or CT chest
- Sputum x3 if coughing or cavitary lesions
Evaluate risk of reactivation treatment
- INH 300 daily x9 mo with pyridoxine
- baseline liver enzymes and vision testing

Standard regimen (9INH):
- Nine months of isoniazid with daily vitamin B6
Alternative shorter courses:
- 4RIF: not yet in guidelines, but likely preferred. Slightly higher risk of hepatitis.
- 6INH
- 3-4INH/RMP