Table 3. Drug resistance of Mycobacterium tuberculosis isolates and history of tuberculosis treatment.

Drug resistance	History of tuberculosis treatment
	Any	None
	n = 15	n = 65
	n (%)	n (%)
Any of the four drugs	8 (53)	12 (19)	P<0.01
Isoniazid (0.1 μg/mL)	5 (33)	3 (5)	P<0.01
Rifampin (10 μg/mL)	6 (40)	1 (2)	P<0.01
Ethambutol (2.5 μg/mL)	5 (33)	6 (9)	P<0.05
Streptomycin (20 μg/mL)	5 (33)	6 (9)	P<0.05
Isoniazid and rifampin	3 (20)	0 (0)	P<0.01

Drug susceptibility of M. tuberculosis isolates was tested by the absolute concentration method. Critical concentrations were indicated in parentheses. Colony growth of at least 25% at the critical concentration was defined as indicating resistance.

The association between drug resistance of M. tuberculosis and a history of tuberculosis treatment was assessed by Fisher’s exact test.