Evaluation of Xpert MTB/RIF and MODS assay for the diagnosis of pediatric tuberculosis.
BACKGROUND
Tuberculosis (TB) in children is rarely confirmed due to the lack of effective diagnostic tools; only 10 to 15% of pediatric TB is smear positive due to paucibacillary samples and the difficulty of obtaining high-quality specimens from children. We evaluate here the accuracy of Xpert MTB/RIF in comparison with the Micoroscopic observation drug susceptibility (MODS) assay for diagnosis of TB in children using samples stored during a previously reported evaluation of the MODS assay.


METHODS
Ninety-six eligible children presenting with suspected TB were recruited consecutively at Pham Ngoc Thach Hospital in Ho Chi Minh City Viet Nam between May to December 2008 and tested by Ziehl-Neelsen smear, MODS and Mycobacterial growth Indicator (MGIT, Becton Dickinson) culture. All samples sent by the treating clinician for testing were included in the analysis. An aliquot of processed sample deposit was stored at -20°C and tested in the present study by Xpert MTB/RIF test. 183 samples from 73 children were available for analysis by Xpert. Accuracy measures of MODS and Xpert were summarized.


RESULTS
The sensitivity (%) in detecting children with a clinical diagnosis of TB for smear, MODS and Xpert were 37.9 [95% CI 25.5; 51.6], 51.7 [38.2; 65.0] and 50.0 [36.6; 63.4], respectively (per patient analysis). Xpert was significantly more sensitive than smear (P=0.046). Testing of additional samples did not increase case detection for MODS while testing of a second sputum sample by Xpert detected only two additional cases. The positive and negative predictive values (%) of Xpert were 100.0 [88.0; 100.0] and 34.1 [20.5; 49.9], respectively, while those of MODS were 96.8 [83.3; 99.9] and 33.3 [19.6; 49.5].


CONCLUSIONS
MODS culture and Xpert MTB/RIF test have similar sensitivities for the detection of pediatric TB. Xpert MTB RIF is able to detect tuberculosis and rifampicin resistance within two hours. MODS allows isolation of cultures for further drug susceptibility testing but requires approximately one week to become positive. Testing of multiple samples by xpert detected only two additional cases and the benefits must be considered against costs in each setting. Further research is required to evaluate the optimal integration of Xpert into pediatric testing algorithms.
Oxford University Clinical Research Unit, Hospital for Tropical Diseases, 764 Vo Van Kiet, District 5, Ho Chi Minh City, Vietnam.
Nguyen Thi Quynh
NT
Nhu
Dang Thi Minh
DT
Ha
Nguyen Duc
ND
Anh
Do Dang Anh
DD
Thu
Tran Ngoc
TN
Duong
Nguyen Dang
ND
Quang
Nguyen Thi Ngoc
NT
Lan
Tran Van
TV
Quyet
Nguyen Thi Bich
NT
Tuyen
Vo Thi
VT
Ha
Do Chau
DC
Giang
Nguyen Huy
NH
Dung
Marcel
M
Wolbers
Jeremy
J
Farrar
Maxine
M
Caws
D000293:Adolescent; D001431:Bacteriological Techniques / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D024881:Drug Resistance, Bacterial; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000302:isolation & purification; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012293:Rifampin / Q000494:pharmacology; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis*
D011933:Reagent Kits, Diagnostic; D012293:Rifampin