Novel hypertonic saline–sodium hydroxide (HS–SH) method for decontamination and concentration of sputum samples for Mycobacterium tuberculosis microscopy and culture

Abstract

This study evaluated a new decontamination and concentration (DC) method for sputum microscopy and culture. Sputum samples from patients with suspected pulmonary tuberculosis (TB) (n=106) were tested using the proposed hypertonic saline–sodium hydroxide (HS–SH) DC method, the recommended N-acetyl-l-cysteine–sodium citrate–sodium hydroxide (NALC-NaOH) DC method and unconcentrated direct smear (Ziehl–Neelsen) techniques for the presence of mycobacteria using Löwenstein-Jensen culture and light microscopy. Of 94 valid specimens, 21 (22.3 %) were positive in culture and were further characterized as Mycobacterium tuberculosis. The sensitivity for acid-fast bacilli (AFB) smears was increased from 28.6 % using the direct method to 71.4 % (HS–SH) and 66.7 % (NALC-NaOH) using DC methods. Both concentration techniques were highly comparable for culture (kappa=0.794) and smear (kappa=0.631) for AFB. Thus the proposed HS–SH DC method improved the sensitivity of AFB microscopy compared with a routine unconcentrated direct smear; its performance was comparable to that of the NALC-NaOH DC method for AFB smears and culture, but it was methodologically simpler and less expensive, making it a promising candidate for evaluation by national TB control programmes in developing countries.