[Persistent positive baciloscopy after several months of tuberculosis therapy: not always it represents a treatment failure].

International agencies for tuberculosis (TB) control (WHO, IUATLD, KNCV) consider the presence of acid-fast bacilli (AFB) in the sputum smear after completion of TB therapy as treatment failure. We describe a case of a pulmonary TB patient who received and correctly completed 6 months of antituberculous treatment with a positive AFB sputum smear. Treatment was continued and sputum cultures were performed for resistance determination. After 9 months, despite the persistence of AFB in the sputum smear, the treatment was suspended because none of the sputum samples yielded a positive culture, indicating no viable bacilli. In addition, the patient was asymptomatic and had recovered his body weight. An exhaustive review of medical literature allowed us to conclude that a positive sputum smear after therapy has been detected in up to 5% of cases and does not always represent a treatment failure as defined by international guidelines. For scenarios where culture methods are not available we propose a scheme to evaluate these patients. This includes compliance with the treatment, severity of the disease at the moment of diagnosis, clinical symptoms after specific therapy and rate of in vitro resistance of M. tuberculosis in the community.