研究
Application on GeneXpert on bronchoscopic samples in the clinical management of patients suspicious of Tuberculosis
日期: 2017-11-13
作者: Dr. TO Kin Wang
摘要: Background: There is limited experience on clinical use of GeneXpert on bronchoalveolar lavage (BAL) fluid samples obtained from patients clinically suspected of pulmonary tuberculosis (TB) in intermediate burden settings. Methods: sputum acid-fast-bacilli (AFB) smear negative patients were offered bronchoscopy. BAL fluid was collected for AFB smear, TB culture, Cobas Taqman TB polymerase chain reaction (PCR) and for GeneXpert. Cases were diagnosed as TB if any one of the tests was positive. Results: From December 2014 to February 2017, 227 samples were collected. Patients’ mean (SD) age was 60.7 (15) years, 143 patients were males and 84 were females. Cough and haemoptysis were the presenting symptoms in 70% and 37.4% respectively. Apical shadows in chest X-ray (CXR) and apical cavitations in computed tomography (CT) were more common in GeneXpert positive cases (p=0.01 and 0.02 respectively). Sensitivities and specificity of GeneXpert was 80% and 98% respectively. The positive predictive value and negative predictive value was 92.3 and 95.1% respectively. There were 9 false negative GeneXpert samples (8 were Cobas Taqman TB PCR negative): 6 were diagnosed by BAL culture, 2 by biopsy and one by Cobas Taqman TB PCR. There were 3 false positive cases with negative culture, 2 were put on empirical treatment with favorable clinical responses, while one defaulted followed up. Conclusion: GeneXpert in BAL samples has high specificity and similar performance as Cobas Taqman PCR to rule in TB for initiating early treatment in clinical suspicious cases. However, it cannot replace other investigations as the only test for diagnosing pulmonary TB.
Optimizing MGIT pyrazinamide susceptibility testing using a reduced inoculum
日期: 2016-07-31
作者: Dr. YAM Wing Cheong
摘要: Among the 150 culture isolates, 11 isolates failed in the MGIT 960 PZA susceptibility test due to under inoculums size (3 isolates for both standard and reduced inoculums; 8 isolates for reduced inoculums only). The failure rate for standard and reduced inoculums was 1.8% (3/171) and 6.4% (11/171) respectively. Only 139 isolates were eligible for further study and analysis. Another 21 archived PZA resistant strains collected between 2003-2013 were also included for comparative study. However, one strain was later confirmed to be PZA susceptible that 140 PZA susceptible and 20 PZA resistant strains were used for the McNemar’s analysis, indicating there is no significant difference between standard and reduced inoculums for MGIT960 PZA susceptibility test (p = 0.6171; Odd Ratio = 1; 95% CI: 0.072 – 13.796). The 20 PZA resistant archived strains collected between 2003-2013 were further characterized by MGIT960 PZA (standard and reduced inoculums) test, PZase activity and DNA sequencing to identify pncA mutations. The most common PZA resistant mutations at pncA were G162D and I90S. Novel mutations including insertions and deletions were also detected among PZA resistant strains. PZase activity were negative for all PZA resistant strains while 20 randomly selected PZA susceptible strains were positive to PZase activity with no mutations in the pncA gene. One strain (WC036) reported as PZA susceptible by TB Reference laboratory (PHLSB) was confirmed resistant to PZA by MGIT960 (both standard and reduced inoculum) with pncA mutations and negative for PZase activity. Another strain (WC205) reported as susceptible to all first line drugs but resistant to PZA was also confirmed susceptible to PZA by MGIT960 (both standard and reduced inoculum) with wild type pncA and positive for PZase activity. In this study, testing 160 M. tuberculosis isolates indicated no significant difference between standard and reduced inoculums for MGIT960 PZA susceptibility test (p >0.05). The failure rate for standard and reduced inoculums was 1.8% and 6.4% respectively. The 1 false susceptible and 1 false resistant isolates reported by TB reference Laboratory (PHLSB) was probably accounted by the drug susceptibility test other than MGIT960. Since 2014, PHLSB has adopted the MGIT960 system with standard inoculums size for routine service to all Hospital Authority Hospitals in Hong Kong. For routine PZA MGIT 960 susceptibility testing using standard inoculums, clinical isolates reported as resistant to PZA should be confirmed by PZase activity and pncA gene mutation analysis using PCR-sequencing.