Validation of the line-probe assay for rapid detection of rifampicin-resistant Mycobacterium tuberculosis in Vietnam.
BACKGROUND
Delays in identifying multidrug-resistant tuberculosis (MDR-TB) contribute to higher TB morbidity and mortality, and ongoing transmission. The line-probe assay (LiPA) is a rapid, commercially available polymerase chain reaction based assay that detects most mutations in the rpoB gene for rifampicin (RMP) resistance. We validated and compared this assay with conventional drug susceptibility testing (DST).


METHODS
We re-cultured a random sample of stored isolates known to be either RMP-resistant or RMP-susceptible according to DST (proportion method). We performed a blinded comparison between LiPA and conventional DST. Genetic sequencing of the rpoB gene was performed on RMP-resistant isolates and discordant results.


RESULTS
We tested 79 RMP-resistant and 64 RMP-susceptible strains. Concordance of LiPA with DST was 94%. For detecting RMP resistance, LiPA sensitivity was 90% and specificity was 100%. Molecular analysis of possible false-negative isolates by LiPA revealed an absence of mutations in the rpoB gene. RMP resistance was a good proxy for MDR-TB, as 66 (93%) of 71 RMP-resistant isolates were also isoniazid-resistant.


CONCLUSIONS
The LiPA provided rapid results that were highly predictive of RMP resistance and MDR-TB. False-negatives occurred, but only among isolates with mutations in regions not assessed by LiPA. Performance and cost-effectiveness should be evaluated in patients during routine program conditions.
Shah
N S
NS
International Research and Programs Branch, Division of TB Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. sshah@montefiore.org
Lan
N T N
NT
Huyen
M N T
MN
Laserson
K
K
Iademarco
M F
MF
Binkin
N
N
Wells
C
C
Varma
J K
JK
D000904:Antibiotics, Antitubercular / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D001681:Biological Assay / Q000379:methods* / Q000706:statistics & numerical data; D012321:DNA-Directed RNA Polymerases; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006801:Humans; D016013:Likelihood Functions; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000706:statistics & numerical data*; D012293:Rifampin / Q000494:pharmacology; D012680:Sensitivity and Specificity; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis / Q000235:genetics / Q000382:microbiology*; D014744:Vietnam
D000904:Antibiotics, Antitubercular; D001426:Bacterial Proteins; C505805:rpoB protein, Mycobacterium tuberculosis; D012321:DNA-Directed RNA Polymerases; D012293:Rifampin