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Open Access Research article

High yield of culture-based diagnosis in a TB-endemic setting

Anne-Marie Demers12, Suzanne Verver34, Andrew Boulle5, Robin Warren6, Paul van Helden6, Marcel A Behr78* and David Coetzee5

Author affiliations

1 Département de Microbiologie et Immunologie, Université de Montréal, Montreal, QC, Canada

2 CHU Sainte-Justine, 3175 Chemin de la Côte Sainte-Catherine, Montréal, QC, H3T 1C5, Canada

3 KNCV Tuberculosis Foundation, The Hague, The Netherlands

4 CINIMA, Academic Medical Centre Amsterdam, Amsterdam, The Netherlands

5 Centre for Infectious Disease Epidemiology and Research, School of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa

6 DST/NRF Centre of Excellence for Biomedical TB Research/ US/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Department of Biomedical Sciences, Faculty of Health Sciences - Stellenbosch University, PO Box 19063, Tygerberg, 7505, South Africa

7 Department of Medicine, McGill University, Montreal, Québec, Canada

8 McGill University Health Centre, Room A5.156, 1650 Cedar Avenue, Montreal, QC, H3G 1A4, Canada

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Citation and License

BMC Infectious Diseases 2012, 12:218  doi:10.1186/1471-2334-12-218

Published: 14 September 2012

Abstract

Background

In most of the world, microbiologic diagnosis of tuberculosis (TB) is limited to microscopy. Recent guidelines recommend culture-based diagnosis where feasible.

Methods

In order to evaluate the relative and absolute incremental diagnostic yield of culture-based diagnosis in a high-incidence community in Cape Town, South Africa, subjects evaluated for suspected TB had their samples processed for microscopy and culture over a 21 month period.

Results

For 2537 suspect episodes with 2 smears and 2 cultures done, 20.0% (508) had at least one positive smear and 29.9% (760) had at least one positive culture. One culture yielded 1.8 times more cases as 1 smear (relative yield), or an increase of 12.0% (absolute yield). Based on the latter value, the

    n
umber of cultures
    n
eeded to
    d
iagnose (NND) one extra case of TB was 8, compared to 19 if second specimens were submitted for microscopy.

Conclusion

In a high-burden setting, the introduction of culture can markedly increase TB diagnosis over microscopy. The concept of number needed to diagnose can help in comparing incremental yield of diagnosis methods. Although new promising diagnostic molecular methods are being implemented, TB culture is still the gold standard.

Keywords:
Tuberculosis; Diagnosis; Culture; Microscopy