Drug-resistance in patients with pulmonary tuberculosis presenting at chest clinics in Hong Kong

Abstract

Specimens of sputum were obtained from 869 newly-registered patients, considered likely to have bacteriologically positive pulmonary tuberculosis, in the 4 main tuberculosis clinics in Hong Kong and flown to London for culture and sensitivity testing to isoniazid, streptomycin and PAS. In all, 247 (28·4%) specimens were negative on smear and culture, 47 (5·4%) positive on smear but negative on culture and 571 (65·7%) grew on culture. Only 4 (0·5%) cultures were contaminated. There were 5 anonymous mycobacteria. All 564 strains of Myco. tuberculosis were classified as the human variety. Smear-positive but culture-negative results were obtained in 23% of specimens which were scantily positive on smear. Climatic conditions, the time in transit, loss of viability of isoniazid-resistant organisms and courses of previous chemotherapy did not explain this incidence. The patients were interrogated about their history of previous chemotherapy on registration, at 1 month and at 6 months; the latter 2 interrogations provided very little extra information. Of the 564 patients with sensitivity test results, 302 (54%) had no history of previous chemotherapy, 54 (10%) had a history of probable chemotherapy and 208 (37%) a history of definite previous chemotherapy. Of the 302 patients with no history of previous chemotherapy, 20% had drug resistance to 1 or more drugs, namely, to 1 drug in 14%, to 2 drugs in 5% and to all 3 drugs in 2%. The total resistance to isoniazid was 14%, to streptomycin 11% and to PAS 3%. Double drug resistance to isoniazid and streptomycin occurred in 5% of patients. Of the 208 patients with a history of definite chemotherapy, 70% had drug resistance to 1 or more drugs, namely, to 1 drug in 35%, to 2 drugs in 25% and to all 3 drugs in 11%. The total resistance to isoniazid was 62%, to streptomycin 41% and to PAS 13%. Double drug resistance to isoniazid and streptomycin occurred in 23% of patients, to isoniazid and PAS in 1% and to streptomycin and PAS in 0·5% of patients. Isoniazid resistance was found in 14% of patients with no history of previous chemotherapy, in 40% of patients with a history of previous chemotherapy which did not include definite isoniazid, and in 67% of patients with a history which included definite isoniazid therapy. Streptomycin resistance occurred in 11% of patients with no history of chemotherapy, in 27% of patients who had received courses of injections and in 43% of patients who had a history of a course of definite streptomycin. there were statistically significant associations between the number of injections and also the number of definite streptomycin injections and the likelihood of finding streptomycin resistance. PAS resistance was found in 3% of patients with no history of previous chemotherapy, in 10% of patients with a history of chemotherapy which did not include PAS and 20% of patients with a history of definite PAS therapy. Of 110 patients with a history of definite chemotherapy received in Hong Kong, 57% had drug resistance compared with 85% of 98 patients who had received chemotherapy elsewhere, the difference being due to the incidence of isoniazid resistance, namely, 45% and 83%, respectively. Patients whose sputum smears were graded as heavy or moderate on direct examination were more likely to be excreting drug-resistant organisms than patients whose smears were graded as scanty or negative. In Hong Kong a careful history in patients newly-registered at a clinic is a valuable guide to the likelihood of finding drug-resistant strains.