WHO and CDC Definition for Extensively Drug-Resistant Mycobacterium tuberculosis

 

Analysis: in vitro antibiotic susceptibility

 

Criteria for extensively drug-resistant Mycobacterium tuberculosis - the isolate is:

(1) resistant to isoniazid

(2) resistant to rifampin

(3) resistant to one or more fluoroquinolones

(4) resistant to one or more of the injectable second-line drugs (amikacin, kanamycin, capreomycin)

 

Observations:

(1) In vitro susceptibility testing to fluoroquinolones, amikacin, kanamycin and capreomycin are more reproducible than testing to other second-line antibiotics.

(2) Infections with M. tuberculosis resistant to fluoroquinolones and the injectable second-line drugs tend to have poor treatment outcomes.