Latent Tuberculosis

From the Canadian TB standards:

Who to test for LTBI?

• Contacts of a known case
• Immigrants to Canada within the past 2 years
• Healthcare workers or those at high risk of nosocomial exposure
• Immunosuppressed patients (HIV, transplant, high dose steroids, TNF-alpha, etc.)
• Radiographic evidence of possible old TB without symptoms and no diagnosis

Diagnosis:

• Mantoux test (PPD) 5-TU intradermal injection
• Read at 48-72 hours
• Record the number of millimetres of induration (raised area, not just red) without rounding
  

False negative:

• Severe illness including active TB
• Malnutrition
• Immunosuppression (iatrogenic, HIV, etc)
• Major viral illness

False positive:

• Allergy to PPD
• Previous fully treated TB
• BCG (see below)
• Non-TB mycobacterial sensitization

Treatment:

1. Exclude active disease
2. INH 300mg PO OD x 9 months +/- Vitamin B6 25mg PO OD
   OR
   RIFAMPIN 600mg PO OD x 4 months
   

NNT~10 for reactivation in the general population. Risk reduction from ~10% to 1% lifetime of reactivation. Lower NNT in at-risk groups.