Smear Microscopy for Diagnosis of Pulmonary Tuberculosis in Eastern Sudan

Abstract EN

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.