NOVEL METHOD FOR PROCESSING RESPIRATORY SPECIMENS FOR DETECTION OF MYCOBACTERIA BY USING C-18-CARBOXYPROPYLBETAINE - BLINDED STUDY

A novel method for processing respiratory specimens to improve culture and acid-fast staining of mycobacteria is introduced. This new method utilized methyl-N-(n-octadecyl)-N-(3-carboxypropyl)ammonium inner sal t (Chemical Abstract Service no. 78195-27-4), also known as C-18-carbo xyropylbetaine (CB-18). In a blinded, five-center study, CB-18-based p rocessing was compared to the standard method combining NALC and NaOH (NALC/NaOH). A total of 573 respiratory specimens were tested. Individ ual specimens were split approximately equally; the host institutions processed half of each specimen by the NALC/NaOH method, while the oth er half was processed with CB-18 at Quest Diagnostics-Baltimore. A tot al of 106 specimens were culture positive for acid-fast bacilli (AFB). Replacement of the primary decontamination agent with CB-18 caused ch anges in all diagnostic parameters. Aggregate culture sensitivity impr oved by approximately 43% (P < 0.01), and smear sensitivity improved b y approximately 58% (P < 0.01). The sensitivity of smear relative to t hat of M. tuberculosis isolates exceeded 93% (P < 0.01) when specimens were processed with CB-18. The average times to a positive result wer e reduced by 7.3 days in liquid culture (P < 0.01) and 5.3 days on sol id media (P < 0.05); however, the CB-18 method had a 20.8% contaminati on rate in liquid culture versus a rate of approximately 7.5% with NAL C/NaOH processing. There were also unusual reductions in liquid cultur e sensitivity and smear specificity among CB-18-processed specimens. T he characteristics of the latter parameters suggested that refinement of the CB-18 processing method should allow further improvements in cu lture sensitivity. This study showed that the CB-18 method has the pot ential to improve both smear and culture detection for these important human pathogens.