Efficacy and safety of short-term bleach digestion of sputum in case-finding for pulmonary tuberculosis in Ethiopia

BACKGROUND: In many settings, the diagnosis of pulmonary tuberculosis depends on sputum microscopy. However, this technique has low sensitivity. We studied the efficacy and safety of sputum digestion with bleach prior to Ziehl-Neelsen (ZN) staining.

METHODS: Positive sputum smears were assessed for staining quality and viability of mycobacteria after varying bleaching times. Two hundred smears were then prepared from the first, second and third sputum sample of tuberculosis suspects. Equal amounts of 5% bleach were added to the remaining first sputum and ZN smears were prepared.

FINDINGS: Optimal quality and staining was achieved with 30–45 min of bleaching. No growth was observed from positive samples after 15 min. Bleached specimens had 26% (52/200) positivity compared to 17.5% (35/200) of unbleached smears (P < 0.001). The bleached smears had 92.3% sensitivity, 93.4% specificity, 78.3% and 97.7% positive and negative predictive values, respectively, against a case definition. Ten patients failed to submit a second or third sputum. Six patients were positive on either the standard or bleach-digested smears, or both.

INTERPRETATION: Bleach digestion is simple, cheap and kills mycobacteria. Its positivity rate is as good as three standard smears. This method has the potential to improve over-burdened services in developing countries.