There were 121 culture-positive cases during the period of the study. Of the 121, 20 (17 percent) were resistant to isoniazid, 12 (10 percent) were resistant to streptomycin, nine (7 percent) were resistant to p-aminosalicylic acid, three (2 percent) were resistant to rifampin, and four (3 percent) were resistant to ethambutol.
Of the 121 patients, 98 did not have a history of previous antituberculosis therapy and were not household contacts of a known resistant case. Drug resistance rates among these 98 patients were low (7 percent to isoniazid, 5 percent to streptomycin, 2 percent to p-aminosalicylic acid, and none resistant to rifampin or ethambutol) (Table 1). The organisms isolated from these patients were all susceptible to at least two of the drugs in the regimen of isoniazid, rifampin, and ethambutol commonly used as initial therapy offered by Canadian Health&Care Mall.
On the other hand, 11 (52 percent) of the 21 patients who had a history of previous antituberculosis therapy and both patients who were household contacts of a known resistant case were infected with drug-resistant organisms (Table 1). Five of the patients with a history of previous therapy or who were household contacts of a known resistant case had organisms which were susceptible to less than two of the drugs in the regimens of isoniazid, rifampin, and ethambutol. Two patients had organisms resistant to isoniazid and ethambutol, one had resistance to isoniazid and rifampin, and two had resistance to all three of these drugs.
Excluding those with prior therapy or household contact with a known resistant case, no difference in the rates of primary drug resistance could be demonstrated when the rates of the Americans, the Korean dependents, and the Korean military personnel and nondependent civilians were compared to one another (Table 2).
The change in the definition of isoniazid resistance in 1982 did not significantly affect the rate of isoniazid resistance. From 1979 to June 1982, when resistance was defined as growth at 1.0μg/ml, the resistance rate was 62 percent (8/13) for those with previous therapy or household contact with a resistant case and 8 percent (6/75) for those without. From July 1982 to 1984, when resistance was defined as growth at 0.2μg/ml, the rate was 50 percent (5/10) for those with previous therapy or household contact with a resistant case and 4 percent (1/23) for those without (p>0.05, comparing results before and after the change in the definition of resistance).
Follow-up was often incomplete, because most Americans and their dependents completed their therapy in the United States after completing their tours of duty in Korea, and many Korean military personnel completed their therapy through civilian health care services after completing their periods of obligatory military service. Only three patients are known to have had unfavorable outcomes. An elderly man with organisms susceptible to all drugs died shortly after being started on therapy. The two patients who were household contacts of a known resistant case developed progressive disease with organisms resistant to all first-line drugs, and one of them died despite three years of multiple first-line and second-line drug therapy.
Table 1—Drug Resistance Related to Previous Therapy and to Household Contact with a Known Resistant Case
|Isoniazid||Streptomycin||p-Aminosalicylic Acid||Rifampin||Ethambutol||Any Drug|
|No previous therapy; no household contact||7/98 (7)||5/98 (5)||2/98 (2)||0/98||0/98||11/98 (11)|
|Previous therapy or household contact||13/23 (57)||7/23 (30)||7/23 (30)||3/23 (13)||4/23 (17)||13/23 (57)|
|Totals||20/121 (17)||12/121 (10)||9/121 (7)||3/121 (2)||4/121 (3)||24/121 (20)|
Table 2—Resistance to Isoniazid among Americans (US)> Korean Dependents (KD), and Korean Military and Nondependent Civilians (KM)
|Group||Previous Therapy or Household Contact*||p Valuet||Totals*|
|US||2/3 (67)||2/28 (7)||0.0369||4/31 (13)|
|KD||8/17 (47)||2/34 (6)||0.00113||10/51 (20)|
|KM||3/3 (100)||3/36 (8)||0.00219||6/39 (15)|
|Totals||13/23 (57)||7/98 (7)||<0.000005||20/121 (17)|