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

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

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.

• 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

• 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

Procedure for GeneXpert processing

1. Starting up system 2. Identifying

corresponding cartridge

4. Loading cartridge 3. Scanning cartridge

onto the machine

Boehme C, Nabeta P, Hilleman D, et al., NEJM 2010; 363:1005-1015

• 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

Results of Specimen Testing

• 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

• 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:

• EDCTP

• Ministry of Health

• HIV patients(KDH-MoH)

• CDC-Atlanta team

• KEMRI-CDC, Kisian

• Kisian TB Lab staff

Acknowledgements

For more information please contact:

KEMRI/CDC

P.O. Box 1578

Kisumu, Kenya

E-mail: info@ke.cdc.gov

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