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Using treatment failure under effective directly observed short-course chemotherapy programs to identify patients
M C Becerra1, J Freeman, J Bayona
1Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA. mbecerra@post.harvard.edu
Setting:
Public ambulatory care centers in three districts of northern metropolitan Lima, Peru.
Objective:
To document drug resistance patterns of isolates of Mycobacterium tuberculosis from patients identified as treatment failures under a model tuberculosis (TB) control program based on directly observed, short-course chemotherapy (DOT-SCC).
Design:
Case series.
Results:
In a referred, consecutive sample of 173 patients identified as treatment failures on DOT-SCC, 160 (92.5%) had culture-positive TB. Of those 160, 150 (93.8%) had active, pulmonary multidrug-resistant TB (MDR-TB, resistance to at least isoniazid [INH] and rifampicin [RIF]). Sixty of the 150 (40.0%) had isolates resistant to at least INH, RIF, ethambutol (EMB) and pyrazinamide (PZA), the initial first-line empiric treatment regimen used locally. Forty-four (29.3%) had isolates resistant to at least INH, RIF, EMB, PZA and streptomycin (SM), the first retreatment regimen. This series of patients had isolates resistant to a mean of 4.5 of the ten drugs tested. The local profile of multidrug resistance is very different from that obtained from national data from Peru.
Conclusion:
In this setting, treatment failure on DOT-SCC is strongly predictive of active MDR-TB. Because of existing local drug resistance patterns in northern Lima, 89.3% of MDR-TB patients identified as treatment failures will receive ineffective therapy with two or fewer secondary TB drugs if they are given the five-drug empiric retreatment regimen endorsed by the World Health Organization. Further short-course chemotherapy for these patients would only serve to amplify ominous existing drug resistance patterns.