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DATA ANALYSIS
The sensitivity, specificity, predictive values and diagnostic accuracy for Xpert™ MTB/Rif in
comparison to culture and DST as the gold standard will be calculated. Analysis will be done
per patient applying the following diagnostic rules as outlined in the table below. Additionally,
the secondary endpoints time to detection of TB and rifampicin resistance, time to TB treatment
and time to MDR treatment, and time to reporting case detection and MDR will be calculated.
Time to detection will be calculated for all tests per sputum from the date of the sputum
collected on which the test was performed to the date that the result is available. Time to
appropriate treatment and time to clinical reporting will be calculated per patient from the time
of first sputum collection from the patient. Indeterminate rates will be calculated out of all tests
performed.
Diagnosis
Description
Smear-positive
•
•
≥ 1+ smear (≥10/100 fields) or ≥ 2 scanty-positive smears
Smear positives with only negative or contaminated cultures will be excluded
from analysis.
Scanty-positive smear
•
•
1-9 AFB per 100 fields
≥ 2 scanty positive smears with 2 negative or contaminated cultures will be
excluded from analysis.
Culture-positive
≥ 1 LJ and/or MGIT culture growth confirmed MTB complex.
Cross-Contamination: A single LJ culture with
≤ 20 colonies or a single MGIT
culture with MTB growth ≥28 days per patient will be excluded from analysis.
NTM: Specimens with growth of mycobacteria other than MTB complex only will be
excluded from analysis.
Contaminated culture
•
•
•
LJ: Cultures completely overgrown by bacterial or fungal contaminations within
3 weeks (discarded). In case of mixed cultures, isolated MTB colonies
transferred to new LJ tube (repeat culture).
MGIT: Instrument positivity w/o detection of AFB.
Contaminated culture results only, among all available cultures, will lead to
exclusion from analysis.
Xpert™ MTB/Rif
positive
Xpert™ MTB/Rif
resistant case
Xpert™ MTB/Rif invalid
case
Non-TB case
Xpert™ MTB results “TB positive”.
Indeterminate cases
(excluded from
analysis)
Excluded from analysis as indeterminate cases will be patients not meeting
inclusion criteria or with incomplete case report forms; sputum 1 and 2
collected >7 days away; no culture done; no valid culture result due to
contamination; no valid Xpert™ MTB/Rif result; smear-positive, culturenegative; single positive culture with <20 colonies on LJ or >28 days on MGIT;
culture-positive at follow-up only; culture-positive but missing speciation;
culture-positive but NTM only and discrepant RIF in conventional DST.
Xpert™ MTB “Rif resistance detected”
Persistent “invalid” or “error” or “no result” after repetition (whenever possible).
• Smear negative, culture-negative patient without TB treatment on the basis
of clinical criteria.
• For Xpert™ MTB/Rif or Culture positive patients and random controls, a
follow-up at 2 and 6 months with repeated clinical and bacteriological workup will be required to exclude TB with the highest possible likelihood. Only if
the bacteriological work-up remains negative, the patient is called Non-TB.
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