Sensitivity, Specificity, and Reproducibility of the Capilia TB-Neo Assay

Abstract

bThe performance of the Capilia TB-Neo assay, a new-generation assay, was assessed by determining its sensitivity, specificity, reproducibility, and cross-reaction with contaminating organisms. The sensitivity and specificity were 99.2 and 96.4% and 89.3 and 100% in pure and mixed-culture isolates, respectively. The kappa statistic was 95.0 and 77.9% in pure and mixed culture isolates, respectively. There was no cross-reaction with contaminating organisms. The Capilia TB assay is a rapid, simple, and inexpensive identification test for identification of mycobacterial culture isolates that has been evaluated extensively (1-7). A new generation of this assay, the Capilia TB-Neo assay (Capilia), has been developed, replacing the original assay (Y. Namba, 8 September 2010, European patent application EP 2226635 A1). The original assay has been shown to have sensitivity and specificity ranging from 92% to 100% (1, 2, 6). Cross-reaction with other mycobacteria and other bacteria has been demonstrated with the original assay (1, 7; Y. Namba, 8 September 2010, European patent application EP 2226635 A1). As a result, a new assay was developed to replace the original assay to take care of the cross-reaction and to improve the specificity (Y. Namba, 8 September 2010, European patent application EP 2226635 A1). So far, there are only two published studies that have evaluated this next-generation assay, and the studies show conflicting results. An overall reduction in sensitivity and specificity was observed by Gomathi et al. (8)-76% and 86%, respectively. However, Pokam et al. reported a sensitivity and specificity approaching 100%, comparable to those of the original assay (9).The study was conducted on isolates from an ongoing study that is evaluating the use of the GeneXpert MTB/RIF test (Xpert) in Lusaka, Zambia. Sputum samples were collected from suspected tuberculosis (TB) and confirmed TB patients attending routine services for whom Xpert detected TB or TB with rifampin resistance and from 10% of those for whom Xpert did not detect TB, for quality assurance, confirmation of rifampin resistance, and treatment monitoring purposes. The study had ethical approval from the University of Zambia Ethics Committee, and all patients provided written informed consent before submitting sputum samples for mycobacterial culture.Sputum specimens were decontaminated using the N-acetyl-L-cysteine (NALC)-NaOH method and were inoculated in a manual mycobacterial growth indicator tube (MGIT; BD) according to standard operating procedures (10, 11). All growth-positive tubes were subjected to Ziehl-Neelsen (ZN) staining, and the Capilia test was performed on all culture isolates confirmed to contain acid-fast bacilli (AFB). Capilia test-negative isolates were confirmed using the GenoType Mycobacterium Common Mycobacteria (GTM_CM) test (Hain Lifescience, Nehren, Germany). Further, isolates from patients with Mycobacterium tuberculosis/ Xpert-detected rifampin resistance were confirmed using the MTBDRplus assay as part of protocols for the ...

Capilia™ TB-Neo assay: a new tool for rapid distinction between tuberculous and non-tuberculous mycobacteria

“…[3][4][5] Consistent with previous reports, the Capilia TB-Neo assay demonstrated a specificity of 100%. 7,11 We observed a sensitivity of 97%, higher than reported by Gomanthi et al but similar to that reported by Muyoyeta et al and lower than those reported by Pokam et al and Chikamatsu et al 6,7,11,12 Reactivity with NTM such as M. avium, M. kansasii, M. fortuitum, M. gordonae, M. chelonae, M. peregrinum and other micro-organisms, such as Nocardia spp., K. pneumoniae, P. aeruginosa, E. coli, S. aureus, C. albicans and P. mirabilis, was checked and a cross-reaction was confirmed as absent for all of these as well as for the negative cultures tested. Although we detected no false-positive results, we did detect three false-negative results.…”

“…The existence of false-negative results on Capilia TB-Neo was not further evaluated, but it may have been due to one of the following reasons: either the mpb64 gene was deleted, as previously reported for some Evaluation of the Capilia TB-Neo assay BCG strains, such as substrains of the Pauster and Glaxo strains, 7,13 or the mpb64 gene was mutated, leading to the production of an incomplete protein. 6,7 Despite the false-negative results, we found the sensitivity of the Capilia TB-Neo to be similar to that observed for AccuProbe (96.8%). 14 Unlike the molecular method, the IC test is a rapid one-step test (15 min after positivity of cultures), that is less expensive and does not require sample preparation, trained technicians or sophisticated equipment.…”

“…The Capilia TB-Neo assay is an improved version of Capilia TB and, although this second generation Capilia test has been validated in some laboratories, as with the first generation test, falsenegative results due to mutations in the mpb64 gene have been reported. [6][7][8][9] In the present study, we evaluated the performance of the Capilia TB-Neo assay at the Clinical Pathology Department of the São João Hospital Centre, Porto, Portugal, in identifying MTC by comparing it with our routine molecular identification methods.…”

Practical Guidance for Clinical Microbiology Laboratories: Mycobacteria

“…The Capilia TB-Neo assay is a second-generation test that eliminated previous cross-reactions with certain NTM and nonmycobacterial bacteria to improve specificity (210). Due to mutations (most commonly due to a 63-bp deletion at position 196) in the gene encoding MPB64, the test gave false-negative results for some M. bovis BCG and, more recently, M. africanum variants (211)(212)(213).…”

“…Several factors have been shown to impact the results of IGRAs (206)(207)(208)(209)(210)(211)(269)(270)(271)(272)(273)(274). Preanalytical factors such as the amount of time from blood collection to incubation can significantly affect IGRA results (269).…”