الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Tuberculosis continues to be a leading infectious cause of death worldwide. The emergence of drug-resistant TB necessitates an urgent fast, highly sensitive diagnostic methods. Several commercial broth-based systems and molecular tests have been established. However, these methods are away from the reach of laboratories in most developing countries due to high cost and the need for complex infrastructure facilities.
The aim of the present study was to evaluate MODS assay and GeneXpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis (MTB) and drug susceptibility for sputum specimens from suspected TB patient for rapid detection of MDR & XDR –TB.
We enrolled 120 patients, suspected clinically & radiologically as pulmonary tuberculosis, in this study. Sputum specimens were collected and subjected to direct ZN smears microscopic examination, LJ culture, MODS assay and GeneXpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis (MTB) and drug susceptibility for INH, RIF, OFX, LEV and KAN drugs.
In the current study, out of 120 sputum specimens; 45(37.50%) were positive by direct ZN smear, 47(39.17%) by LJ culture, 51(42.50%) by MODS assay and 72(60%) by GeneXpert assay. Regarding new cases, out of 82 sputum specimens; 13(15.85%) were positive by direct ZN smear, 31(37.80%) by LJ culture, 34(41.46%) by MODS assay and 37(45.12%) by GeneXpert. While for cases with previous antituberculous treatment; out of 38 sputum specimens; 32(84.21%) were positive by direct ZN smear, 16(42.11%) by LJ culture, 17(44.74%) by MODS assay and 35(92.11%) by GeneXpert.
A higher prevalence of pulmonary TB in males than females was observed in the current study. where in males, 41(87.23%) were positive LJ culture while in females only 6(12.77%) showed positive LJ culture.
In the current study, results revealed that out of 120 sputum specimens; 47 specimens were positive by LJ culture, out of these 28 (59.57%) were positive in both culture and direct ZN smear giving a sensitivity of 59.56%. While out of 73 specimens negative by LJ culture; 17 (23.29%) were positive by direct ZN smear giving a specificity of 76.71%. As regards new cases, sensitivity and specificity were 41.94% and 100% respectively while for cases with previous antituberculous treatment ZN smear‘s sensitivity and specificity were 93.75% and 22.73% respectively.
Regarding evaluation of MODS for detection of MTB, the present study showed that out of 120 sputum specimen 51(42.50%) specimens were positive by MODS assay. Results showed that out of 47 sputum specimens that were positive by LJ culture; 46 (97.87%) were also positive by MODS assay and only 1(2.13%) was negative by MODS assay but it was positive by GeneXpert. While out of the 73 specimens that were negative by LJ culture, only 5(6.85%) were positive by MODS assay. The sensitivity of MODS assay for the 120 specimens included in this study compared to culture was 97.87%, while the specificity was 93.15%. As regards new cases, sensitivity and specificity were 96.77% and 92.16% respectively while for cases with previous antituberculous treatment the sensitivity and specificity were 100% and 95.45% respectively.
The current study showed that the sensitivity of GeneXpert for sputum specimens compared to LJ culture for all 120 cases was 100%, while the specificity was 65.75%. Also the sensitivity of GeneXpert for all sputum specimens compared to combined culture results (LJ and MODS assay) was 100%, while the specificity was 70.59%. Regarding new cases, the sensitivity and specificity of GeneXpert compared to LJ culture were 100% and 88.24% respectively while the sensitivity and specificity of GeneXpert compared to combined culture (LJ culture & MODS assay were 100% and 95.75% respectively. As regards cases with previous antituberculous treatment, the sensitivity and specificity of GeneXpert compared to LJ culture were 100% and 13.64% respectively while the sensitivity and specificity of GeneXpert compared to combined culture (LJ culture & MODS assay were 100% and 14.29% respectively
In present study the time required for the recovery of mycobacteria was significantly shorter in MODS assay, mean time was 10.69± 1.892 days, than in LJ medium with a mean time was 33.04 ±4.369 days. The period of the maximum isolation was the second week for MODS assay (90.20%) of isolates in comparison to the 5th week for LJ medium (63.83%) of isolates. Moreover, MODS assay revealed DST results on the same day of MTB detection while LJ culture needed more time after isolation of M. tuberculosis for applying the proportion method to obtain DST results.
MODS assay has an added advantage of performing antibiotic sensitivity for multiple drugs (1st line drugs) at the same time of MTB detection, this study further investigated OFX, LEV and KAN from 2nd line drugs. The present study showed that the sensitivity of MODS assay compared to the proportion method for detection of INH resistance was 100% while specificity was 97.56%. Regarding RIF resistance, this study showed total agreement between both the proportion method and MODS assay, giving a sensitivity of 100%, specificity of 100%. Regarding fluoroquinolone resistance (OFX &LEV) in this study; sensitivity of MODS assay for OFX was 81.82%, while the specificity was 97.14%. As regard LEV, the sensitivity was 100%, while the specificity was 97.78%. The sensitivity of MODS assay for KAN was 75%, while the specificity was 97.62%.
Regarding MDR isolates, this study showed that out of 46 isolated strains, 4 isolates were found to be MDR by both proportion method and MODS assay, while the remaining 42 isolates were not MDR giving a concordance of 100%.
Regarding GeneXpert results in the present study, out of 120 specimens; MTB was detected in 72(60%) and rifampicin resistance was not detected in 65(54.17%) cases, while 4 (3.33%) cases were resistant to RIF and 3(2.50%) cases were indeterminate. In the current study the four cases detected as RIF-resistant by the GeneXpert MTB/RIF assay, were confirmed to be MDR-TB by 1% proportion method and MODS assay giving a sensitivity of 100%, specificity of 100%.
This study concluded that MODS assay showed high sensitivity, specificity and more early diagnosis of TB and drug susceptibility in both new cases and cases with previous anti tuberculous treatment. Thus it can be used for rapid detection of MDR and XDR-TB. Moreover, GeneXpert showed high sensitivity for diagnosis of TB in new cases. However it revealed high sensitivity 100% but low specificity (60%) in smear negative cases under antituberculous treatment. GeneXpert can accurately screen MDR/RR-TB among re-treatment PTB patients, reducing the turn-around time for appropriate therapy initiation.