2
Key Points
➤ TB disease remains one of the major causes of morbidity and
mortality in the world.
➤ The emergence of drug-resistant tuberculosis has become apparent
over the past 2 decades—in particular, multidrug-resistant
tuberculosis (MDR-TB; resistant to isoniazid and rifampin) and
extensively drug-resistant tuberculosis (XDR-TB; resistant to isoniazid
and rifampin, plus any fluoroquinolone and at least 1 of 3 injectable
second-line drugs [ie, amikacin, kanamycin, or capreomycin]).
Transmission
➤ Mycobacterium tuberculosis (Mtb) is transmitted from person
to person via the airborne route. Several factors determine the
probability of Mtb transmission:
1. Infectiousness of the source patient: A positive sputum smear for acid-fast bacilli
(AFB) or a cavity on chest radiograph are strongly associated with infectiousness.
2. Host susceptibility of the contact.
3. Duration of exposure of the contact to the source patient.
4. The environment in which the exposure takes place. A small, poorly ventilated space
provides the highest risk.
5. Infectiousness of the Mtb strain.
➤ Those who are household contacts and are exposed to patients who
are smear positive have higher rates of both infection and disease.
➤ Medical procedures that generate aerosols of respiratory secretions,
such as sputum induction and bronchoscopy, entail significant risk for
Mtb transmission unless proper precautions are taken.
Testing for Latent Tuberculosis Infection (LTBI)
See page 11 for an explanation of the Recommendation Grading.
➤ The panel recommends performing an interferon-γ release assay
(IGRA) rather than a tuberculin skin test (TST) in individuals ≥5
years of age who meet the following criteria (S-M):
• are likely to be infected with Mtb
• have a low or intermediate risk of disease progression
• it has been decided that testing for LTBI is warranted and
• either have a history of BCG vaccination or are unlikely to return to have their
TST read.
Remarks: A TST is an acceptable alternative, especially in situations where an IGRA is
not available, too costly, or too burdensome.
Diagnosis
