Early detection of MDRTB by molecular tools in the control of drug resistant tuberculosis in Portugal: a case of success.

Multidrug resistant tuberculosis (MDRTB) represents a threat to public health and a challenge to tuberculosis (TB) con-trol programs. From 1994 to 1997, Portugal had an incidence of 48.3 new cases of TB per 100 000 inhabitants and an average of 22.7% of these cases were MDRTB, the highest in Western Europe. In an attempt to assist the National Health Authorities in the control of TB, we implemented in 2002 with the support of Fundação Calouste Gulbenkian, the “TB Fast-Track” program as part of the TB Task Force of Greater Lisbon, involving 12 Lisbon hospitals and based on the use of the BACTECTM MGIT 960 system, coupled with the direct identification of M. tuberculosis complex (MTBC) and the de-tection of mutations in the rpoB gene, using the INNOLiPA Rif.TB Assay (LiPA) (Innogenetics). Because mutations in the rpoB result in resistance to rifampicin (RIF), and resistance to RIF is almost always accompanied by resistance to isoniazid (INH), this approach allowed us to identify the MDRTB patient within 24-48 hours. A full report confirming identification and antibiotic susceptibility (AST) of MTBC by conventional methods (BACTEC culture plus AST and Accuprobe ID) was issued within additional 12 days.From September 2002 to January 2006, the LiPA assay was directly applied to630 acid fast positive respiratory speci-mens. The comparison between data from this assay and conventional methods revealed 84 discrepancies. The 11 false positive results corresponded to patients with therapy already established by the time of specimen sampling, whereas the 73 false negative resulted from inhibition of amplification. A total of 487 of the 600 MTBC positive isolates were susceptible to all 5 first-line anti-TB drugs. The frequency of MDRTB (resistant to at least INH plus RIF) was 10%. From the 63 MTBC resistant to RIF, 62 were detected by the LiPA as carrying mutations S531L (60 isolates), H526Y and D516V (1 isolate each). No mutation was detected by LiPA for one sample, repeatedly identified as resistant by AST. Detection of rpoB mutations proved to be a good surrogate marker for MDRTB, since only 2 out of 600 MTBC isolates were monoresistant to RIF. The early detection of active TB, particularly the detection of MDRTB, is essential for the success of any TB control program. The application of molecular techniques for the early identification of MDRTB assisted the National Health Authorities in the reduction of MDRTB rates in Lisbon to less than 8% (average 2003 to 2007)