Pooling sputum from multiple individuals for Xpert® MTB/RIF testing: a strategy for screening high-risk populations

SETTING: Symptom-based screening for tuberculosis (TB) disease is limited by poor performance of symptom screening in several key populations. We tested the hypothesis that pooling sputum from multiple individuals for Xpert® MTB/RIF testing would reduce the number of tests required while retaining an acceptable sensitivity, thus allowing the use of Xpert for TB screening.METHODS: We compared pooling ratios that would require the least number of assays using Xpert and determined that for a population with a TB prevalence of approximately 3%, a 1:5 pooling ratio is optimal. To evaluate sensitivity, we generated pools of one specimen with known Mycobacterium tuberculosis culture positivity (smear microscopy-positive or -negative) with four culture-negative specimens.RESULTS: All 20 of the pools generated from a smear- and culture-positive sputum sample were positive using Xpert. Of the 22 pools with a smear-negative, culture-positive sample, we included 17 in the analysis, of which 13 (76%) were Xpert-positive.CONCLUSIONS: Pooling of sputum samples using Xpert achieved reasonable sensitivity and warrants further evaluation of the systematic screening of high TB prevalence populations.