New simple decontamination method improves microscopic detection and culture of mycobacteria in clinical practice

Nora Morcillo¹, Belén Imperiale¹, Juan Carlos Palomino²

¹Reference Laboratory of Tuberculosis Control Program of Buenos Aires Province, Dr. Cetrángolo Hospital, Buenos Aires, Argentina; ²Mycobacteriology Unit Institute of Tropical Medicine, Antwerp, Belgium

Abstract: This study was carried out at Dr. Cetrángolo Hospital, Buenos Aires, Argentina. The objective was to compare two digestion–decontamination procedures: the N-acetyl-Lcysteine–sodium citrate–NaOH (NALC-NaOH) and a combination of 7% NaCl plus NaOH, the hypertonic saline–sodium hydroxide (HS-SH) method, in detection and recovery of mycobacteria. Microscopy detection rates before and after concentration of specimens by both methods, were also compared. The study had two phases. Phase I: comparison of the gold standard NALC-NaOH and HS-SH on paired samples involving respiratory clinical specimens by means of receiver operating characteristic curve analysis. Phase II: blinded, randomized trial to assess the performance of HS-SH versus NALC-NaOH in clinical practice. Phase I: Positive microscopy rate was significantly increased in around 2.2% after concentration in comparison to that of specimens without concentration. The calculated sensitivity values for microscopy detection increased between 15.2% (HS-SH: 73.5%) to 16.7% (NALC-NaOH: 75.0%) over those without concentration (58.3%). Phase II: similar diagnostic rates by microscopy and cultures were obtained by either HS-SH or NALC-NaOH. The clinical performances were also very similar. These results and the low cost of the HS-SH procedure indicate the possibility of its implementation in clinical laboratories with high burden of tuberculosis cases and low resources.

Keywords: tuberculosis, diagnosis, clinical practice