comparison of performance between zn microscopy and ... · detection of mycobacterium tuberculosis...
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Albert Okumu
06th EDCTP Forum
09th - 13th Oct , 2011
Comparison of performance between ZN microscopy and GeneXpert in MTB detection in sputum specimens at KEMRI/CDC TB laboratory
Okumu A1, Orina F1, Musau S1, Cavanaugh S2, McCarthy K2, Heather A2, Modi S2 , Laserson K1, Cain K1
Affiliation:
1 – KEMRI/CDC Research and Public Health Collaboration
2 – Centers for Disease Control and Prevention, CDC-Atlanta
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Tuberculosis is a major public health threat in Kenya, where 100,000 new cases are reported annually, and approximately 50-60% are HIV-infected.
Detection of Mycobacterium tuberculosis (Mtb) usually depends on Ziehl Neelsen (ZN) microscopy, but this has been shown to be insensitive, especially in persons with HIV.
Xpert MTB/RIF, an automated PCR-based assay, with high sensitivity and turn-around time of under 2 hours, has potential to revolutionize Mtb detection.
We studied the added value of this test compared to ZN microscopy in people with HIV enrolled in a study of TB screening and diagnosis in Nyanza province, Kenya.
Background
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TB Burden in Kenya
• Kenya ranked 13th out of the 22 countries with the most TB, according to the WHO
• Nyanza Province has greatest TB burden in Kenya
– TB notification: 440/100,000
– 20% of all notified TB cases in Kenya
– Only 2.6% of notified TB cases were reported in children aged 0-14 years
• 75% of TB patients are HIV co-infected, while (52%) nationally.
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• To compare yield of ZN smear microscopy
and Xpert MTB/RIF assay for Mtb in people
with HIV.
Purpose:
1. ZN smear with
positive TB bacilli
2. Xpert PCR result with
Rif resistance detected
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• Sputum specimens from people with HIV
were subjected to both ZN microscopy and
Xpert MTB/RIF at KEMRI/CDC TB laboratory.
• We compared the diagnostic yield of these
tests.
Methodology:
1. Microscopy ( ZN) 2. Cepheid GeneXpert
MTB Rif machine
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Procedure for GeneXpert processing
1. Starting up system 2. Identifying
corresponding cartridge
4. Loading cartridge 3. Scanning cartridge
onto the machine
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Boehme C, Nabeta P, Hilleman D, et al., NEJM 2010; 363:1005-1015
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• From October 2010 to December 2010, a
total of 262 specimens were tested with ZN
microscopy and Xpert MTB/RIF.
• Of those, 34 of 262 (13%) were positive by
Xpert MTB/RIF but only 8 of 262 (3%) were
also positive by ZN microscopy.
• 26/34(76%) TB diagnoses would have been
missed by ZN microscopy alone.
Results
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Results of Specimen Testing
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• More work to validate the Xpert assay(s), as
it seems appropriate for POC centres, since
it is user friendly, fast and efficient
• Since it shows MTBc id and Rif. resistance
results, its helpful in pt. management
Recommendations
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• Xpert MTB/RIF more than quadrupled,
(76%) of TB diagnostic testing in specimens
from people with HIV. Given the high
mortality rate of undiagnosed TB in people
with HIV, this could save many lives.
Conclusions/summary:
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• EDCTP
• Ministry of Health
• HIV patients(KDH-MoH)
• CDC-Atlanta team
• KEMRI-CDC, Kisian
• Kisian TB Lab staff
Acknowledgements
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For more information please contact:
KEMRI/CDC
P.O. Box 1578
Kisumu, Kenya
E-mail: [email protected]
The findings and conclusions in this report are those of the authors and do not necessarily represent the official
position of the Centers for Disease Control and Prevention.
Thank you