The diagnostic accuracy of urine-based Xpert MTB/RIF in HIV-infected hospitalized patients who are smear-negative or sputum scarce |
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Authors: | Jonathan G Peter Grant Theron Tapuwa E Muchinga Ureshnie Govender Keertan Dheda |
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Institution: | Lung Infection and Immunity Unit, Division of Pulmonology & UCT Lung Institute, Department of Medicine, University of Cape Town, Cape Town, South Africa. |
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Abstract: | BackgroundHospitals in sub-Saharan Africa are inundated with HIV-infected patients and tuberculosis (TB) is the commonest opportunistic infection in this sub-group. Up to one third of TB-HIV co-infected patients fail to produce a sputum sample (sputum scarce) and diagnosis is thus often delayed or missed. We investigated the sensitivity of urine-based methods (Xpert MTB/RIF, LAM strip test and LAM ELISA) in such patients.Methodology/Principal Findings281 HIV-infected hospitalised patients with clinically suspected TB provided a spot urine sample. The reference standard was culture positivity for Mycobacterium tuberculosis on ≥1 sputum or extra-pulmonary sample. MTB/RIF was performed using 1 ml of both unprocessed and, when possible, concentrated urine. Each unconcentrated urine sample was also tested using the Clearview LAM ELISA and Alere LAM strip test. 42% (116/242) of patients had culture-proven TB. 18% (20/54) were sputum scarce. In sputum-scarce patients, the sensitivity of urine MTB/RIF and LAM ELISA was 40% (95%CI: 22–61) and 60% (95%CI: 39–78), respectively. Urine MTB/RIF specificity was 98% (95%CI: 95–100). Combined sensitivity of urine LAM ELISA and MTB/RIF was better than MTB/RIF alone MTB/RIF and LAM: 70% (95%CI: 48–85) vs. MTB/RIF: 40% (95%CI: 22–61), p?=?0.03]. Significant predictors of urine MTB/RIF positivity were CD4<50 cells/ml (p?=?0.001), elevated protein-to-creatinine ratio (p<0.001) and LAM ELISA positivity (p<0.001). Urine centrifugation and pelleting significantly increased the sensitivity of MTB/RIF over unprocessed urine in paired samples 42% (95%CI: 26–58) vs. 8% (95%CI: 0–16), p<0.001]. Urine MTB/RIF-generated CT values correlated poorly with markers of bacillary burden (smear grade and time-to-positivity).Conclusions/SignificanceThis preliminary study indicates that urine-based MTB/RIF, alone or in combination with LAM antigen detection, may potentially aid the diagnosis of TB in HIV-infected patients with advanced immunosuppression when sputum-based diagnosis is not possible. Concentration of urine prior to MTB/RIF-testing significantly improves sensitivity. |
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