Isoniazid-resistant tuberculosis. A community outbreak and report of a rifampin prophylaxis failure.

The choice of effective preventive treatment for persons exposed to Mycobacterium tuberculosis resistant to isoniazid is uncertain. Although no data document the efficacy of any drug other than isoniazid for preventive treatment of tuberculosis, rifampin, with or without ethambutol, has been used for prophylaxis in contacts of cases with known isoniazid-resistant organisms. This report describes a community outbreak of isoniazid-resistant tuberculosis infection and a case of rifampin prophylaxis failure with acquired rifampin resistance. This raises concern about the efficacy of rifampin for the preventive treatment of contacts exposed to isoniazid-resistant tuberculosis.