Date Published: July 3, 2017
Publisher: Public Library of Science
Author(s): Crispin Lumbala, Paul R. Bessell, Pascal Lutumba, Sylvain Baloji, Sylvain Biéler, Joseph M. Ndung’u, Ana Paula Arez.
We carried out a study to compare the performance, in terms of sensitivity and specificity, of the new SD BIOLINE® HAT rapid diagnostic test (RDT) with the card agglutination test for trypanosomiasis (CATT) for diagnosis of human African trypanosomiasis (HAT) in the Democratic Republic of the Congo (DRC). Participants were enrolled actively by four mobile teams, and passively at four health facilities in three provinces. Consenting participants were tested concurrently with the RDT and CATT on whole blood. Those found positive by either test were tested with CATT on serial dilutions of plasma, and with a parasitological composite reference standard (CRS). Cases were only the individuals found positive by the CRS, while controls were negative by both CATT and RDT, as well as those that were positive by CATT or RDT, but were negative by the CRS, and had no history of HAT. Over five months, 131 cases and 13,527 controls were enrolled. The sensitivity of the RDT was 92.0% (95% confidence interval (CI) = 86.1–95.5), which was significantly higher than CATT (sensitivity 69.1%; 95% CI = 60.7–76.4). The sensitivity of CATT on plasma at a dilution of 1:8 was 59.0% (95% CI = 50.2–67.2). The specificity of the RDT was 97.1% (95% CIs = 96.8–97.4) while that of CATT was 98.0% (95% CIs = 97.8, 98.2) and specificities of algorithms involving CATT at 1:8 dilution were 99.6% (95% CI = 99.5–99.7). Reproducibility of results was excellent. We concluded that an algorithm in which the SD BIOLINE® HAT RDT is used for screening is optimal for case detection in both passive and active screening settings. However, the lower specificity of the RDT compared to that of CATT would result in a larger number of false positive individuals undergoing confirmatory testing.
Human African trypanosomiasis (HAT), also known as sleeping sickness, is a vector-borne parasitic disease transmitted to humans by the bite of an infected tsetse fly (Glossina spp). The disease is endemic in sub-Saharan Africa, within the limits of the geographic distribution of the tsetse fly. Two sub-species of the protozoan parasite Trypanosoma brucei cause the disease in humans: T.b. gambiense and T.b. rhodesiense. Infection with T.b. gambiense causes the chronic form of HAT (gambiense HAT) and accounts for more than 95% of cases . Gambiense HAT is endemic in rural, resource-limited settings, mainly in west and central Africa, with the majority of cases reported in the Democratic Republic of the Congo (DRC) . The number of cases of HAT reported globally has been falling steadily, and the disease is now targeted for elimination as a public health problem by 2020 .
This study has demonstrated that the SD BIOLINE® HAT RDT had a higher sensitivity in both active and passive screening, with a difference of 23% between it and the second best screening test—CATT (Table 1 and Fig 3). However, this is at the expense of a slightly lower specificity of the RDT, which would result in some additional workload in confirmatory testing. The simplicity and stability of the HAT RDT has created a great opportunity to improve screening coverage of the population at risk, as it can be deployed to any health facility in endemic areas. There were no issues regarding reproducibility–the agreement between readers was very good for both CATT and the RDT. However, there was a case that would have been missed if there was just one reader for each test, which highlights the importance of training and diligence of staff who are reading the tests.
This study has demonstrated that the SD BIOLINE® HAT RDT has superior sensitivity when screening for gambiense HAT in both active and passive screening settings in the DRC. However, it still misses at least 8% of the cases, meaning that there remains scope for developing other screening tests with better performance. Other test combinations that were tested here offer better specificity, which would require further investigations in cost-effectiveness analysis to determine the optimal combination, especially for accelerated and sustained elimination of the disease. The RDT would also benefit from further testing in other settings. Serological tests with improved accuracy, if they can be developed, could then be used as true diagnostic tests, without the need for confirmation, and might also be used for the identification of asymptomatic carriers of HAT . In the event that drugs that are safer and easier to use become available [33–35], a “test and treat” strategy would be feasible , thus accelerating elimination of the disease.