Mycobacterium kansasii pulmonary infection: a prospective study of the results of nine months of treatment with rifampicin and ethambutol. Research Committee, British Thoracic Society.

BACKGROUND: Pulmonary disease caused by Mycobacterium kansasii is reported in approximately 50 new patients in Britain annually. Rifampicin and ethambutol are effective in vitro but the optimal duration of treatment, and whether isoniazid should also be given, are uncertain. The British Thoracic Society has conducted a prospective, multicentre study of the treatment of this condition with rifampicin and ethambutol given for nine months.

METHODS: One hundred and seventy three patients with two or more positive cultures and radiological evidence of disease were recruited via the Mycobacterium Reference Unit (PHLS) in Cardiff from 113 physicians in England, Scotland, and Wales. Rifampicin and ethambutol were given for nine months, other antituberculosis drugs being discontinued once the culture was identified as M kansasii. Patients were reviewed, sputum cultured, and chest radiographs performed before, during, and at regular intervals for 51 months after chemotherapy.

RESULTS: The mean (SD) age was 55.5 (11.7) years, 73% were men, and 50% had other lung problems. Cavitation was seen in 88%, bilateral shadowing in 48%, and three or more lung zones were affected in 46%. All cultures were sensitive to rifampicin and ethambutol but resistant to isoniazid and pyrazinamide. One patient who took chemotherapy irregularly still had positive cultures at seven and eight months. Fifteen patients developed positive cultures after the end of chemotherapy; factors which might account for the relapse were identified in eight. Reinfection rather than relapse was suspected in three of the 15. Radiographic improvement stabilised within three years in 80%.

CONCLUSIONS: M kansasii pulmonary infection responds well to nine months of treatment with rifampicin and ethambutol but patients who contract this disease have a high mortality rate from other causes. Isoniazid does not appear to be a necessary part of the regimen.