Evaluation of the tuberculosis culture color plate test for rapid detection of drug susceptible and drug-resistant Mycobacterium tuberculosis in a resource-limited setting, Addis Ababa, Ethiopia

Abstract

Timely diagnosis of tuberculosis (TB) is limited in Ethiopia. We evaluated the performance of a low technology, thin layer agar, Mycobacterium tuberculosis ( M . tb ) culture color plate (TB-CX) test with concurrent drug susceptibility testing (DST) to isoniazid (INH), rifampin (RIF), and pyrazinamide (PZA) directly from sputum specimens. Patients undergoing examination for TB and multidrug-resistant (MDR)-TB were enrolled in Addis Ababa, Ethiopia from March 2016 to February 2017. All subjects received a GeneXpert MTB/RIF PCR test. TB-CX test results were compared to reference Löwenstein–Jensen (LJ) culture for M . tb detection and DST for susceptibility to INH and RIF. Kappa statistic was applied to test agreement between results for TB-CX test and the reference methods, a cut-off Kappa value of 0.75 was considered as high level of agreements. A total of 137 participants were analyzed: 88 (64%) were new TB cases, 49 (36%) were re-treatment cases. The TB-CX test detected M . tb and DST in an average of 13 days compared to 50 days for the conventional DST result. The sensitivity and specificity of the TB-CX test for detecting M . tb were 94% and 98%, respectively (concordance, 96%; kappa 0.91). The sensitivity of the TB-CX test to detect drug resistance to INH, RIF, and MDR-TB was 91%, 100%, and 90% respectively. The specificity of the TB-CX test for detecting INH, RIF, and MDR-TB was 94%, 40%, and 94% respectively. Overall agreement between TB-CX test and LJ DST for detection of MDR-TB was 93%. The TB-CX test showed strong agreement with the GeneXpert test for detecting M . tb (89%, kappa 0.76) but low agreement for the detection of RIF resistance (57%, kappa 0.28). The TB-CX test was found to be a good alternative method for screening of TB and selective drug resistant-TB in a timely and cost-efficient manner.

Successful introduction of the Colour Test into inexperienced settings

“…and used approximately a week after production, but when the CT would be used routinely in a diagnostic laboratory using direct patient specimen, it would be helpful to have a longer expiration date in order to pour more plates at once. Other study groups have used CT plates with expiry terms even up to four months [25], yet it needs to be investigated, whether such a prolongation changes the diagnostic performance of the test when the media is prepared on site.…”

“…for isoniazid (INH), rifampicin (RIF) and ciprofloxacin (CFX) [23]. In former studies, where the performance of CT was evaluated, the media was prepared in an expert laboratory elsewhere and transported into the study site or the specimens from the study site were transported into an expert laboratory for testing [24,25]. Hence, the preparations of the media represent a constraint of the CT method.…”

“…Hence, the preparations of the media represent a constraint of the CT method. On the other hand, the performance of CT has been evaluated in the role of a direct test for both detection of TB and DST [25][26][27][28]. Furthermore, CT has been studied as a method for indirect DST on multidrug resistant (MDR)-TB isolates with promising results [23,29].…”

New Developments and Insights in the Improvement of Mycobacterium tuberculosis Vaccines and Diagnostics Within the End TB Strategy

“…Novel culture-based approaches have been developed to reduce time to positivity and simultaneously screen for drug susceptibility during culture, meeting the need for a rapid DST test (one of the four TPPs identified by the WHO/FIND). These recent developments include the fully automated liquid-based Mycobacteria Growth Indicator Tube (MGIT) [ 58 ], and the color plate agar-based culture test [1 st Generation (1G) TB-CX], among others [ 59 ]. Although commercial liquid culture-based DST platforms such as BD BACTEC MGIT can provide reliable results within a few days, liquid culture is prone to contamination and requires extensive laboratory infraestructure, specialized personnel, instrument calibration and maintenance, specialized reagents, etc., limiting wide implementation in low-income settings.…”

“…Although commercial liquid culture-based DST platforms such as BD BACTEC MGIT can provide reliable results within a few days, liquid culture is prone to contamination and requires extensive laboratory infraestructure, specialized personnel, instrument calibration and maintenance, specialized reagents, etc., limiting wide implementation in low-income settings. In contrast, the 1G TB-CX test is based on the rapid, simple and inexpensive thin-layer agar method, and includes DST testing using a four quadrant agar plate, allowing for the early detection of MDR and pre-XDR strains (average of 13 days when compared to the 50 days required for a standard DST), with a 94% sensitivity [ 59 , 60 ]. Despite a limited number of studies in very specific settings, the 1G TB-CX test, at the cost of US$1.35, has the potential to be a good alternative method for the fast and low-cost diagnosis of DS and MDR TB in countries with poor health infraestructure [ 59 ].…”