OptimisingMycobacterium tuberculosisdetection in resource limited settings

Abstract

ObjectivesThe light-emitting diode (LED) fluorescence microscopy has made acid-fast bacilli (AFB) detection faster and efficient although its optimal performance in resource-limited settings is still being studied. We assessed the optimal performances of light and fluorescence microscopy in routine conditions of a resource-limited setting and evaluated the digestion time for sputum samples for maximum yield of positive cultures.DesignCross-sectional study.SettingFacility-based involving samples of routine patients receiving tuberculosis treatment and care from the main tuberculosis case referral centre in northern Nigeria.ParticipantsThe study included 450 sputum samples from 150 new patients with clinical diagnosis of pulmonary tuberculosis.MethodsThe 450 samples were pooled into 150 specimens, examined independently with mercury vapour lamp (FM), LED CysCope (CY) and Primo Star iLED (PiLED) fluorescence microscopies, and with the Ziehl-Neelsen (ZN) microscopy to assess the performance of each technique compared with liquid culture. The cultured specimens were decontaminated with BD Mycoprep (4% NaOH–1% NLAC and 2.9% sodium citrate) for 10, 15 and 20 min before incubation in Mycobacterium growth incubator tube (MGIT) system and growth examined for acid-fast bacilli (AFB).ResultsOf the 150 specimens examined by direct microscopy: 44 (29%), 60 (40%), 49 (33%) and 64 (43%) were AFB positive by ZN, FM, CY and iLED microscopy, respectively. Digestion of sputum samples for 10, 15 and 20 min yielded mycobacterial growth in 72 (48%), 81 (54%) and 68 (45%) of the digested samples, respectively, after incubation in the MGIT system.ConclusionsIn routine laboratory conditions of a resource-limited setting, our study has demonstrated the superiority of fluorescence microscopy over the conventional ZN technique. Digestion of sputum samples for 15 min yielded more positive cultures.

Diagnostic performance of fluorescent light‐emitting diode microscopy for tuberculous lymphadenitis in a high‐burden setting

“…Lower specificity of LED microscopy compared with conventional ZN microscopy has been reported previously . Most studies found that the specificity of LED microscopy was comparable with that of conventional ZN microscopy.…”

Sensitivitas Metode Pemeriksaan Mikroskopis Fluorokrom dan Ziehl-Neelsen untuk Deteksi Mycobacterium tuberculosis pada Sputum

“…Akan tetapi pada saat ini tersedia mikroskop fluoresen deangan harga yang relatif terjangkau misalnya dengan adanya teknologi LED microscopy 7,8 Hasil penelitian didapatkan bahwa sensitivitas metode pewarnaan ZN dan fluorokrom masing-masing sebesar 70% dan 90%. Sesuai dengan penelitian-penelitian sebelumnya, BTA pada sputum dengan pewarnaan ZN akan menunjukkan hasil positif bila sputum mengandung paling sedikit 10 5 BTA/ml, sedangkan metode pewarnaan yang lebih sensitif seperti fluorokrom dapat mendeteksi BTA dengan jumlah minimal 10 4 BTA/ml 10 14 .…”

Smear Microscopy for Diagnosis of Pulmonary Tuberculosis in Eastern Sudan

“…Assuming a specificity of 98-99% and smear positivity rate of 10%–15%, positive predictive values in the range of 75%–91% would be expected ( Table 2 ) [ 19 ]. Positive predictive values reported by African and Asian investigators vary considerably (60–98%) [ 20 – 26 ]. The heterogeneity of results might be explained by differences in tuberculosis prevalence and smear specificity.…”