A comparison of sodium hypochlorite n-acetyl-l-cystein sputum concentration methods and culture for diagnosis of smear negative pulmonary tuberculosis suspects attending Mulago hospital.

Abstract

The sensitivity of direct sputum smear microscopy is very low, ranging from 25 to 65%. It is thus inevitable that direct smear microscopy needs to be improved or other methods of diagnosis of smear negative (TB) be designed. Several studies have shown a significant increase in sensitivity of smear microscopy by use of Bleach and NALC sputum concentration methods. However, the concentration methods have not been widely adopted in most countries. No literature is available on use of the concentration methods (bleach and NALC) for diagnosis of initially AAFB negative PTB suspects. Objective: To evaluate the diagnostic efficacy of the bleach and NALC sputum concentration methods in comparison to culture for diagnosis of TB in initially AAFB negative PTB suspects. Study methods: This was a cross sectional study with an analytical component. Consecutive adult patients with a productive cough of more than 2 weeks were requested to participate in the study. Two spot and one early morning sputa were screened for AAFBs. Patients who were initially AAFB negative (3 direct smears negative) were recruited into the study. The second and third sputum samples of patients who had consented were pooled and divided into two. The first of the pooled samples was bleach digested, centrifuged, supernatant discarded, sediment fixed and stained by the ZN technique. The second of the pooled samples was digested using NALC, centrifuged and supernatant discarded. The sediment of this second pooled sample was then used for smear preparation, stained ZN technique, while a part of it was also used for inoculation of culture media. Data collection was done using a coded questionnaire after which it was entered and analysed using SPSS version 12 statistical programme. Results: of the 448 patients screened, 89 were smear positive and started on Anti-TB treatment, 237 were initially AAFB negative and met the inclusion criteria. The rest were excluded for various reasons. Compared to culture, the sensitivity and specificity of the bleach concentration method for diagnosis of initially AAFB negative PTB suspects was found to be 26.8% and 97.7% respectively. NALC concentration method had a sensitivity of 31.7% and a specificity of 95.3%. Conclusion: Bleach and NALC sputum concentration methods cannot be adopted as alternatives to LJ culture for detection of TB in initially AAFB negative PTB suspects, due to their very low sensitivities. However, in developing countries where most health units lack culture facilities these methods could still be utilised to accelerate initiation of treatment since TB is curable and the drugs are readily available.