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Tuberc Res Treat. 2018 Jun 14;2018:8038137. doi: 10.1155/2018/8038137. eCollection 2018.

Smear Microscopy for Diagnosis of Pulmonary Tuberculosis in Eastern Sudan.

Author information

1
Research Center Borstel, Borstel, Germany.
2
College of Veterinary Medicine, Sudan University of Science and Technology, Khartoum, Sudan.
3
Institute of Microbiology and Epizootics, Freie Universit├Ąt Berlin, Berlin, Germany.
4
Institute of Endemic Diseases, University of Khartoum, Khartoum, Sudan.
5
Robert Koch Institute, Berlin, Germany.
6
Faculty of Veterinary Medicine, University of Khartoum, Khartoum, Sudan.
7
Karolinska Institute, Stockholm, Sweden.
8
Labor Limbach, Heidelberg, Germany.
9
German Center for Infection Research, Borstel Site, Borstel, Germany.
10
London School of Hygiene and Tropical Medicine, London, UK.

Abstract

Background:

In Sudan, tuberculosis diagnosis largely relies on clinical symptoms and smear microscopy as in many other low- and middle-income countries. The aim of this study was to investigate the positive predictive value of a positive sputum smear in patients investigated for pulmonary tuberculosis in Eastern Sudan.

Methods:

Two sputum samples from patients presenting with symptoms suggestive of tuberculosis were investigated using direct Ziehl-Neelsen (ZN) staining and light microscopy between June to October 2014 and January to July 2016. If one of the samples was smear positive, both samples were pooled, stored at -20┬░C, and sent to the National Reference Laboratory (NRL), Germany. Following decontamination, samples underwent repeat microscopy and culture. Culture negative/contaminated samples were investigated using polymerase chain reaction (PCR).

Results:

A total of 383 samples were investigated. Repeat microscopy categorized 123 (32.1%) as negative, among which 31 were culture positive. This increased to 80 when PCR and culture results were considered together. A total of 196 samples were culture positive, of which 171 (87.3%), 14 (7.1%), and 11 (5.6%) were M. tuberculosis, M. intracellulare, and mixed species. Overall, 15.6% (57/365) of the samples had no evidence of M. tuberculosis, resulting in a positive predictive value of 84.4%.

Conclusions:

There was a discordance between the results of smear microscopy performed at local laboratories in the Sudan and at the NRL, Germany; besides, a considerable number of samples had no evidence of M. tuberculosis. Improved quality control for smear microscopy and more specific diagnostics are crucial to avoid possible overtreatment.

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