Direct Detection by the Xpert MTB/RIF Assay and Characterization of Multi and Poly Drug-Resistant Tuberculosis in Guinea-Bissau, West Africa

Abstract

Background: This study aimed to evaluate the usefulness of the Xpert MTB/RIF assay for the rapid direct detection of M. tuberculosis complex (MTBC) strains and rifampicin resistance associated mutations in a resource-limited setting such as Guinea-Bissau and its implications in the management of tuberculosis (TB) and drug resistant tuberculosis, complementing the scarce information on resistance and genotypic diversity of MTBC strains in this West African country.

Methods and results: This cross-sectional prospective study included 100 consecutive TB patients with positive acid-fast smears at two months of anti-tuberculosis treatment or in a re-treatment situation, between May and December 2012. Resistance to rifampicin was detected using the GeneXpert system and the Xpert MTB/RIF assay. MTBC isolates obtained with the BACTEC MGIT 960 system were tested for susceptibility to first- and second-line anti-tuberculosis drugs. Overall, the prevalence of multidrug-resistant tuberculosis (MDR-TB) was found to be 9 cases. Of these, 67% (6 patients) of confirmed MDR-TB cases had no past history of TB treatment and 33% (3 patients) were previously treated cases. Extensively drug-resistant TB was not found. Molecular typing of the MDR-TB strains revealed recent transmission patterns of imported MDR strains.

Conclusions: The Xpert MTB/RIF assay was reliable for the detection of rifampicin resistant MTBC strains directly from sputum samples of patients undergoing first-line treatment for two months, being more trustworthy than the simple presence of acid-fast bacilli in the smear. Its implementation is technically simple, does not require specialized laboratory infrastructures and is suitable for resource-limited settings when a regular source of electricity and maintenance is available as well as financial and operation sustainability is guaranteed by the health authorities. A high prevalence of MDR-TB among patients at risk of MDR-TB after two months of first-line treatment was found, in support of the WHO recommendations for its use in the management of this risk group.

Fig 1. Flowchart presenting the selected study population.

The diagram describes the criteria used for the selection of the patients included in the study. From the initial 333 patients admitted in the hospital with symptoms of PTB, 100 meet the inclusion criteria and were monitored in the course of the present study. HRF, Hospital Raoul Follereau; TB; Tuberculosis; PTB: Pulmonary tuberculosis; (+), positive; (-), negative.

Fig 2. Dendogram based on the 24-loci MIRU-VNTR and spoligotyping profiles of the eight MDR M. tuberculosis isolates, with positive results with the Xpert MTB/RIF assay in Guinea-Bissau.

The eight strains can be divided in two clades, Beijing and LAM9. Within the Beijing clade, two genetic clusters were detected; one comprised by strains #1 and #90 and the second one by strains #19 and #68. Distance scale is indicated at the bottom (see Methods for further details). SIT, shared international type (from SITVIT WEB database).