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Latent tuberculosis infection — sometimes called inactive TB — is TB
bacteria present in a person who is not ill and not infectious. It can be
treated to prevent TB disease.
The reason to bother is a single statistic:
**Progression from untreated latent TB infection to TB disease accounts for
approximately 80% of U.S. TB cases.**
Most American tuberculosis is not newly caught. It is an old infection waking
up. Which means finding and treating latent infection is not a secondary
activity alongside controlling transmission — it is the main lever there is.
The rule that comes first
Do not start latent TB infection treatment until TB disease is excluded.
Latent infection is treated with fewer drugs than active disease. Giving that
regimen to someone who actually has TB disease is how drug resistance is
manufactured — an inadequate combination against a full bacterial load.
The regimens
**The CDC and the National Tuberculosis Coalition of America preferentially
recommend short-course, rifamycin-based, 3- or 4-month regimens.**
Short-course matters for the same reason travel reimbursement matters in
contact tracing: a well person taking medicine for a disease they do not have
will not do it for nine months, and completion is the only thing that
counts.
Who to treat
| Priority | Criteria |
|---|---|
| High | Known risk factors for developing TB disease, and a positive TB blood test (IGRA) or tuberculin skin test |
| Consider | No known risk factors, with either a positive IGRA or a skin test reaction of 15 mm or larger |
The threshold moves with the risk. A smaller skin test reaction counts in
someone with risk factors; without them, the bar is 15 mm — because in a
low-risk person a smaller reaction is more likely to be a false positive than
an infection.
Source: Centers for Disease Control and Prevention.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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