Isoniazid-resistant tuberculosis in Birmingham, United Kingdom, 1999-2010

Background: There have been few studies on risk factors and treatment outcomes of isoniazid (H)-resistant tuberculosis (TB), and optimal treatment regimens are debated. Aim: To identify risk factors for H-resistant TB, describe treatment regimens and compare these to national guidelines and describe short-term outcomes of H-resistant TB in Birmingham, UK. Design: Retrospective case series. Methods: Cases of H-resistant tuberculosis in Birmingham between January 1999 and December 2010 (n = 89) were compared with drug-susceptible cases (n = 2497). Treatment regimens and outcomes at 12 months from diagnosis were evaluated by case note review. Results: No independent predictors for H-resistant TB were found. For 76/89 (85%) patients with full treatment details available, median treatment duration was 11 months (interquartile range 9-12 months). Only 27/72 (38%) patients with H-monoresistance were treated in line with national guidelines. A further 14/72 (19%) were treated according to other recognized guidelines. Overall treatment success was 75/89 (84%). Treatment failure occurred in 6/89 (7%) patients, all developed multi-drug resistance. Poor adherence was documented in these patients and use of a non-standard regimen in one patient was not thought to have contributed to treatment failure. Conclusions: No discriminating risk factors for early detection of H-resistant TB were found. Treatment regimens in clinical practice were highly varied. H-resistance can drive MDR-TB when there is evidence or suspicion of poor adherence. A low threshold for enhanced case management with directly observed therapy is warranted in this group.