Following TB diagnostic algorithms: could do better

What happens after a negative test for tuberculosis? Evaluating adherence to TB diagnostic algorithms in South African primary health clinics.

McCarthy K, Grant AD, Chihota V, Ginindza S, Mvusi L, Churchyard G, Fielding K. J Acquir Immune Defic Syndr. 2015 Nov 25. [Epub ahead of print]

Introduction and background: Diagnostic tests for tuberculosis (TB) using sputum have suboptimal sensitivity among HIV-positive persons. We assessed health care worker adherence to TB diagnostic algorithms after negative sputum test result/s.

Methods: The XTEND trial compared outcomes among people tested for TB in primary care clinics using Xpert® MTB/RIF vs. smear microscopy as the initial test. We analysed data from XTEND participants who were HIV-positive or HIV status unknown, whose initial sputum Xpert® MTB/RIF or microscopy result was negative. If chest radiography, sputum culture or hospital referral took place, the algorithm for TB diagnosis was considered followed. Analysis of intervention (Xpert® MTB/RIF) effect on algorithm adherence used methods for cluster-randomised trials with small number of clusters.

Results: Amongst 4037 XTEND participants with initial negative test results, 2155 (53%) reported being or testing HIV positive and 540 (14%) had unknown HIV status. Amongst 2155 HIV-positive participants (684 [32%] male, mean age 37 years [range 18-79 years]), there was evidence of algorithm adherence amongst 515 (24%). Adherence was less likely among persons tested initially with Xpert® MTB/RIF vs. smear (14% [142/1031] vs 32% [364/1122], adjusted risk ratio 0.34 [95% CI 0.17-0.65]) and for participants with unknown vs. positive HIV status (59/540 [11%] vs. 507/2155 [24%]).

Conclusions: We observed poorer adherence to TB diagnostic algorithms amongst HIV-positive persons tested initially with Xpert® MTB/RIF vs. microscopy. Poor adherence to TB diagnostic algorithms and incomplete coverage of HIV testing represents a missed opportunity to diagnose TB and HIV, and may contribute to TB mortality.

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Editor’s notes: Despite advances in the TB diagnostic field in recent years, molecular tests such as Xpert® MTB/RIF will still miss a substantial proportion of HIV-positive people with active TB disease. For that reason, diagnostic algorithms have been developed to guide further evaluation of people with symptoms suggestive of TB who test negative with Xpert®. This paper presents findings from South Africa that, in the context of a cluster-randomised trial, few people received further investigation according to the algorithm.

Only one in seven of the HIV-positive people with a negative Xpert® MTB/RIF had any further investigations recorded. Sputum culture was the most common investigation in this group but was done for only around one in ten. It should be noted that the outcome of having further investigations was largely based on review of clinic and laboratory records. As a result, it is possible that additional investigations were performed but remained undocumented. Although considerable between-clinic variation in performance was noted, the reasons underlying this were not explored in this analysis. The algorithm for people living with HIV was not overly complex and was broadly similar to the algorithm in place previously for investigation of people with a negative sputum smear. The observation that algorithm adherence was lower than for people with a negative smear suggests that health care workers might have had false confidence in the negative Xpert® result. In the broader context, this study took place at a time when there was much hype around Xpert® as a tool that would revolutionise the diagnosis of TB. It would not be surprising if this resulted in health care workers being over-confident in their interpretation of negative test results.

There are other possible explanations for the low numbers having additional investigations:

  • People may not have returned for their initial test result so further investigation was not possible (this is not quantified here)
  • People did return but symptoms had fully resolved or they were unable to produce sputum for further investigation
  • Health care workers used clinical judgement to decide on the need for further investigation rather than adhering strictly to the algorithm. This is supported at least partly by the fact that people with more TB symptoms were more likely to receive additional investigations. The yield of culture is not reported here – that might have given a further clue as to whether the people selected to have further investigations were individuals with a high likelihood of TB.  

These issues and others may need to be explored in future analyses to determine whether modifications to the algorithm are required or whether strengthened training and support of health care workers would improve adherence to the algorithm.

Avoid TB deaths
Africa
South Africa
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