Characterization of tuberculosis drug resistance patterns in the early days of XDR-TB

Drug-resistant tuberculosis is considered one of the major threats to tuberculosis (TB) control, namely in the forms of Multidrug-Resistant TB (MDR-TB) and Extensively Drug Resistant TB (XDR-TB). The term XDR-TB was coined in 2005 to describe strains of MDR-TB that are also resistant to fluoroquinolones and second-line injectable drugs. In a 2006 CDC/WHO survey of 17690 isolates of M. tuberculosis, 20% were found to be MDR‐TB and 2% were XDR-TB. Other reports also showed a higher prevalence (53%) of XDR-TB isolates in Portugal. Given this context, we collected data from the Portuguese National Reference Centre for MDR-TB located at the last working Portuguese sanatorium. We conducted a retrospective descriptive study, analyzing the drug susceptibility test (DST) results from then recently admitted drug-resistant TB patients, from 1994 to 1998. All cultures and phenotypic DST were performed in the National Reference Laboratory. A total of 113 patients were included. There were 79 patients (69.9%) fulfilling criteria for MDR-TB and 35 patients (31,0%) for XDR-TB. In the MDR-TB group, 41 patients (36.3%) also presented resistance to ethambutol, 93 (82.3%) to streptomycin, and 19 (16.8%) to pyrazinamide. The resistance pattern for second-line drugs in this group was variable. With regard to the trends in resistance patterns over the study period, we observed a downward trend in the prevalence of resistance to all of the drugs from 1996 forward. Our data confirms the high prevalence of XDR-TB cases in Portugal. Although the exact reasons for this are unknown, we postulate that it may be related to the high percentage of African immigrants from the former Portuguese colonies.