Comparison of direct versus concentrated smear microscopy in detection of pulmonary tuberculosis

Abstract

BackgroundSputum smear microscopy is fast and inexpensive technique for detecting tuberculosis (TB) in high incidence areas but has low sensitivity. Physical and chemical sputum processing along with centrifugation have been found to show promise in overcoming this limitation. Our objective was to compare the sensitivity of smear microscopy obtained with smears made directly from respiratory specimens to those from concentrated specimens.MethodsBy active screening, 915 TB suspects were identified from Dhaka Central Jail and sputum specimens were aseptically collected. Direct smears were prepared by taking a small portion of the purulent part of the sputum with a sterile loop. The specimens were then processed by a standard N-acetyl-L-cysteine-NaOH digestion-decontamination method to prepare concentrated specimens. Both smears were then air dried, heat fixed, and stained by the Ziehl-Neelsen staining technique. The stained slides were examined under oil immersion and were graded following International Union Against Tuberculosis and Lung Diseases guidelines. All the specimens were inoculated into Lowenstein-Jensen (L-J) media and culture results were considered as gold standard to calculate sensitivity.ResultsOf 915 specimens, 73 (8%) specimens were positive both on direct and concentrated methods, one sample was positive on direct microscopy but was negative on concentrated method. An extra 14 (1.5%) samples were positive on concentrated method which were negative on direct smear. In L-J media 105 specimens were found positive for TB bacilli and of them, 74 (70.5%) and 87 (82.9%) were positive in direct and concentrated smear, respectively. The sensitivity of direct and concentrated smear microscopy was different when using positive culture as the gold standard (71% vs. 83%).ConclusionsThe results showed that concentrated technique increases the sensitivity of microscopy up to 12%. Therefore, the national programs in high TB burden countries may consider incorporating the technique into their guidelines at least in the district and higher level laboratories to improve case finding strategy.

Pediatric tuberculosis detection using trained African giant pouched rats

“…Animals were rewarded upon correct identification of known TB-positive control sputum samples. All other rat-indicated samples were preconcentrated by adding 4% sodium hydroxide and centrifuging to obtain sediment for concentrated smear microscopy that is more sensitive than direct smear (15). Results of TB patients found by rats and confirmed by light-emitting diode fluorescence microscopy (LED-FM) (16) were submitted to the respective DOTS center and also to the healthcare workers for tracking the respective patients to start TB treatment.…”

Rapid Detection of Mycobacteria using automated Detection/ Incubation System in Exudative Pleural Effusion in Alexandria Main University Hospital

“…Similarly, reports from numerous researches have revealed different sensitivities for Zeil Neelsen direct smear (Lai et al, 2012;Maurya et al, 2011;Gill et al, 2013;Uddin et al, 2013).…”

“…This finding might consider Bact Alert system a reliable, easy, rapid screening test for tuberculous pleurisy that needs confirmation via other laboratory assays. fluid have been considered to be a rapid diagnostic tool but with a low sensitivity as well as inability to discriminate between actively replicating and dead bacilli (Steingart et al, 2007;Uddin et al, 2013). Similarly, rapid molecular techniques as PCR for detection of TB nucleic acid lacked the ability to discriminate between active and inactive TB cases positive for mycobacterial DNA.…”

Bleach method in comparison with NALC-NaOH specimen processing method for the detection of mycobacterium in sputum specimen

“…It was estimated that two billion people being infected with tubercle bacilli worldwide even after the availability of many highly sensitive diagnostic tools and very efficacious treatment since decades. 1 According to the recent data, in India TB epidemic is greater than previously estimated. 2 There was an estimate of 10.4 million new TB cases worldwide in 2015, among which Asian, Nigerian and South African countries were accounted for 60% of new cases.…”