Discordant rifampicin susceptibility results are associated with Xpert® MTB/RIF probe B and probe binding delay.

SETTING: Xpert® MTB/RIF is the first-line diagnostic test for Mycobacterium tuberculosis and rifampicin (RIF) resistance in South Africa. OBJECTIVE: To describe the rates of Xpert RIF resistance not confirmed on follow-up testing, as well as the patient and test characteristics associated with discordant results. DESIGN: Retrospective review of patients with isolates showing Xpert RIF resistance. Line-probe assay, phenotypic drug susceptibility testing or repeat Xpert were all considered confirmatory tests of RIF resistance. 'Discordance' was defined as a patient with RIF resistance identified on initial Xpert testing, with a subsequent confirmatory test indicating RIF susceptibility. Associations were analysed using Pearson χ² difference of proportions and modified Poisson regression. RESULTS: RIF discordance occurred in 22/263 subjects and was associated with Xpert probe B, probe binding delay, as opposed to probe dropout, and probe binding delays (ΔCt) of between 4 and 4.9. CONCLUSION: Discordant RIF resistance was common in our cohort and was associated with Xpert probe delay and use of probe B.

Can patients afford the cost of treatment for multidrug-resistant tuberculosis in Ethiopia?

SETTING: Ethiopia has a high prevalence of tuberculosis (TB) and is one of the countries with the highest burden of multidrug-resistant TB (MDR-TB). OBJECTIVE: To understand the costs that patients incur in obtaining diagnosis and treatment for MDR-TB. DESIGN: In March 2013, interviews were conducted with 169 MDR-TB patients at three hospitals in Ethiopia to identify the cost to patients and the impact on employment and family income. RESULTS: The average MDR-TB patient incurred a total cost of US$1378, which represented 25 months of a mid-treatment household income of US$54. The impact on the patient's employment and on overall patient and family income was generally catastrophic: 74% of all respondents reported losing their jobs, 66% of patients lost household income, and household income was reduced by 38%. To help cover the costs, 38% of patients sold some type of property, while 7% leased out property and 41% took out loans, any of which could jeopardize their future financial situation even further. CONCLUSION: Despite services being officially free of charge, most patients incurred catastrophic costs and suffered significant income loss as a result of obtaining diagnosis and treatment for MDR-TB.

The complexities of Xpert® MTB/RIF interpretation.

The Xpert(®) MTB/RIF assay has demonstrated robust capability for diagnosing tuberculosis (TB) and rifampin (RMP) resistance. Optimal use of Xpert in diverse settings will require knowledge of challenges when interpreting the results. We present three selected cases from the United States, a low-burden TB setting, to highlight important clinical scenarios encountered with Xpert testing: rapid RMP resistance detection in a patient with pre-extensively drug-resistant TB who immigrated from the Philippines, false-positive RMP resistance detection, and Mycobacterium tuberculosis detection in a culture-negative patient. These cases demonstrate that a low pre-test probability of TB or drug-resistant TB can complicate the interpretation of the Xpert assay.