Evaluation of an acid-fast bacilli autostainer for concentrated sputum smears

Abstract

Setting: An automatic acid-fast bacilli (AFB) stainer was developed to improve laboratory workflow and protect laboratory workers.

Objective: To determine the usefulness of the 7720 Aerospray AFB slide stainer for liquefied and concentrated respiratory specimens.

Design: With 24 smear-positive specimens submitted for AFB stain and culture in a tertiary care hospital, the autostainer was evaluated to determine whether smears would be sloughed from slides during the staining process by loading distilled water instead of staining reagents. With 109 more specimens, the performance of the 7720 Aerospray was compared with manual florescence staining as a gold standard. The tested smears were prepared with Mycohold treatment.

Results: In most cases, the slides exposed to the autostainer containing distilled water showed lower grades of AFB than those slides not exposed to the autostainer (14/24 in Mycohold-treated slides). Almost half (54/109, 49.5%) of the Mycohold-treated autostained smears had a lower grade than the same smears stained manually. Among 62 Mycohold-treated autostained smear-negative specimens, respectively eight (12.9%) and 19 (30.6%) were high and low false-negatives.

Conclusion: The 7720 Aerospray showed poor performance in AFB staining of concentrated sputum specimens.