TB PCR

Useful For

Detection of Mycobacterium tuberculosis complex in AFB smear-positive specimens.

 

Clinical Information

Delayed laboratory confirmation of TB leads to delays in initiation of therapy, potentially inappropriate therapy, and missed opportunities to prevent transmission.

 

There are five closely related mycobacteria grouped in the M. tuberculosis complex: M. tuberculosis, M. bovis, M. africanum, M. microti, and M. canetti. Mycobacterium tuberculosis is transmitted through the airborne route and there are no known animal reservoirs. Mycobacterium bovis may penetrate the gastrointestinal mucosa or invade the lymphatic tissue of the oropharynx when ingested in milk containing large numbers of organisms. Airborne transmission of both M. bovis and M. africanum can also occur (14–16). Mycobacterium bovis BCG is a live-attenuated strain of M. bovis and is widely used as a vaccine for tuberculosis. It may also be used as an agent to enhance immunity against transitional-cell carcinoma of the bladder. When used in this manner, adverse reactions such as dissemination may be encountered, and in such cases M. bovis BCG may be cultured from nonurinary tract system specimens, i.e., blood, sputum, bone marrow, etc.

 

Tuberculosis is spread from person to person through the air by droplet nuclei, particles 1 to 5 µm in diameter that contain M. tuberculosis complex. Droplet nuclei are produced when persons with pulmonary or laryngeal tuberculosis cough, sneeze, speak, or sing. They also may be produced by aerosol treatments, sputum induction, aerosolization during bronchoscopy, and through manipulation of lesions or processing of tissue or secretions in the hospital or laboratory.

 

Tuberculosis remains one of the deadliest diseases in the world. The World Health Organization (WHO) estimates that each year more than 8,000,000 new cases of tuberculosis occur and approximately 3,000,000 persons die from the disease. In Canada 1,577 new active and re-treatment cases were reported to the Canadian Tuberculosis Reporting System (CTBRS) in 2010, corresponding to an incidence rate of 4.6 per 100,000 population. The incidence in 25 – 34 year olds accounted for 18% of the total (6.0 / 100,000), whereas the incidence in those > 74 years old was 9.6 / 100,000. Of all TB cases in 2010 66% were from foreign-born individuals, 21% among Canadian-born Aboriginal people and 12% of cases were among Canadian-born non-Aboriginal people. For 2010, pulmonary TB constituted 64% of all reported cases.

 

Interpretation

TB PCR

POSITIVE: M. tuberculosis complex DNA detected. Therapeutic success or  failure cannot be determined using this test.

NEGATIVE: M. tuberculosis complex DNA NOT detected. A negative PCR result does not exclude the presence of tuberculosis disease. Therapeutic success or failure cannot be determined using this test.

TB PCR limit of detection is approximately 18 colony-forming units (CFU)/mL in sputum specimens.

 

References

American Thoracic Society. Diagnostic Standards and Classification of Tuberculosis in Adults and Children. Am J Repir Crit Care Med. 2000; 161:1376-1395.

Pfyffer, G, and F Palicova. 2011. Mycobacterium: general Characteristics, Laboratory Detection, and Staining Procedures, p 472 – 502, In
Versalovic, J., Carroll, K. C., Funke, G., Jorgensen, J, H., Landry, M. L., and Warnock, D, W. Manual of Clinical Microbiology, 10th ed., vol. 2. ASM Press, American Society for Microbiology, Washington, DC.

 

 

Menzies D., and Khan, K. Diagnosis of tuberculosis infection and disease. In Long, R., and Ellis, E. Eds. Canadian Tuberculosis Standards 6th Ed. Public Health Agency of Canada, 2007.

 

 

Public Health Agency of Canada. Tuberculosis in Canada 2010. Public Health Agency of Canada, Ottawa, ON. 2012.

Roche Molecular Systems Inc. COBAS® TaqMan® MTB Test, 2010. Roche Diagnostics GmbH, Mannheim.

 

Performance

 

Status

Days

Analytic Time

Maximum Laboratory Time

Specimen Retention

AFB Microscopic

Routine

Mon – Fri 24h 24h 1 month

STAT

Mon – Sun 24h 24h 1 month
TB PCR

Routine

Mon – Sun 24h 48h 1 month
Culture

Routine

Mon – Fri 8 weeks 10 weeks 1 month

 

Method Description

AFB Microscopic: Auramine fluorescent microscopy

TB PCR: Realtime TaqMan PCR with probe confirmation

Culture: 1) BACTTEC MGIT Liquid Media, 2) LJ Solid Media

 

Performing Laboratory Location

Newfoundland & Labrador Public Health Laboratory

100 Forest Road

St. John’s, NL A1A 3Z9

 
 

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