Successful Treatment of a Multidrug-Resistant Tuberculosis Patient with a Negative Xpert MTB/RIF Test for Rifampicin-Resistant Tuberculosis in Guizhou Province of China: A Case Report.

The Xpert MTB/RIF (Xpert) assay recommended by the World Health Organization (WHO) can be used to simultaneously detect complex (MTBC) and rifampicin (RIF) resistance associated mutations. However, if Xpert testing results are negative for RIF resistance because mutations outside the RIF resistance-determining region (RRDR) are not detectable by the assay, patients with RIF-resistant/multidrug-resistant tuberculosis (RR/MDR-TB) will be treated inappropriately for several weeks prior to obtaining the drug susceptibility testing (DST) results. Here, we report a rare case of TB in Guizhou Province of China that was identified as RIF-susceptible by the Xpert MTB/RIF assay, but later was confirmed as MDR-TB by DST, and its successful treatment with effective second-line anti-TB drugs. We detected a rare mutation (Ile572Phe) in clinical samples of this patient, highlighting the importance of using other methods such as PCR and sequencing to complement the Xpert MTB/RIF assay for the routine diagnosis of RR/MDR-TB because of the limited scope of the assay. These complementary methods allow for the detection of rare mutations outside the RRDR and can be beneficial when used in geographical locations where such mutations are frequently reported. However, these methods may not be feasible for resource-limited settings.