Peripheral clinic versus centralized laboratory-based Xpert MTB/RIF performance: Experience gained from a pragmatic, stepped-wedge trial in Botswana

Abstract

Background: In 2011, the Botswana National Tuberculosis Program adopted World Health Organization guidelines and introduced Xpert MTB/RIF (Xpert) assay to support intensified case finding among people living with HIV enrolling in care. An evaluation was designed to assess performance under operational conditions to inform the national Xpert scale-up.

Methods: Xpert was implemented from August 2012 through November 2014 with 13 GeneXpert instruments (GeneXpert) deployed in a phased approach over nine months: nine centralized laboratory and four point-of-care (POC) peripheral clinics. Clinicians and laboratorians were trained on the four-symptom tuberculosis screening algorithm and Xpert testing. We documented our experience with staff training and GeneXpert performance. Test results were extracted from GeneXpert software; unsuccessful tests were analysed in relation to testing sites and trends over time.

Results: During 276 instrument-months of operation a total of 3,630 tests were performed, of which 3,102 (85%) were successful with interpretable results. Mycobacterium tuberculosis complex was detected for 447 (14%); of these, 36 (8%) were rifampicin resistant. Of all 3,630 Xpert tests, 528 (15%) were unsuccessful; of these 361 (68%) were classified as "error", 119 (23%) as "invalid" and 48 (9%) as "no result". The total number of recorded error codes was 385 and the most common reasons were related to sample processing (211; 55%) followed by power supply (77; 20%) and cartridge/module related (54; 14%). Cumulative incidence of unsuccessful test was similar between POC (17%, 95% CI: 11-25%) and centralized laboratory-based GeneXpert instruments (14%, 95% CI: 11-17%; p = 0.140).

Conclusions: Xpert introduction was successful in the Botswana setting. The incidence of unsuccessful test was similar by GeneXpert location (POC vs. centralized laboratory). However, unsuccessful test incidence (15%) in our settings was higher than previously reported and was mostly related to improper sample processing. Ensuring adequate training among Xpert testing staff is essential to minimize errors.

Fig 1. Thirteen GeneXpert instruments sites in Botswana.

Fig 2. Error, invalid, and no result rates by quarter following initial implementation October 2012 to November 2014.

Error rates showed increasing trend over 8 quarters, p = 0.008. Invalid rates showed decreasing trend over 8 quarters, p<0.001. No result showed increasing trend over 8 quarters, p = 0.099. Note for Fig 2. By the time of analysis all 13 sites have experienced at least four quarters. Q5 –eleven sites (ATH, WC, BOB, BK8, DRM, EXT, GAN, KAD, LMH, NRH and SDA). Q6 –ten sites (ATH, AWC, BOB, BK8, DRM, GAN, KAD, LMH, NRH and SDA). Q7. Five sites (ATH, AWC, BK8, KAD and LMH). Q8 –two sites (ATH and KAD).