Field Evaluation of Feasibility & Ease-of-Use of Novel Onchocerciasis Diagnostics - Mozambique

Background
Lack of sensitive, specific, point of care diagnostics are a major barrier to the collection of programmatic and research data on onchocerciasis. This project primarily aims to determine the accuracy of the two novel diagnostics, the GADx Ov16 RDT and the DDTD Ov16 and OvOC3261 biplex, by comparing each to the results from the existing SD Bioline Ov16 RDT, and skin snip quantitative polymerase chain reaction (qPCR), during an existing onchocerciasis survey in Mozambique. The aims of the study are:
• To determine the accuracy of the two novel diagnostics, by comparing each to the results from the existing SD Bioline Ov16 RDT, and skin snip qPCR.
• To assess cross reactivity of the two tests with other co-endemic helminth infections, specifically lymphatic filariasis, as assessed by the Filariasis Test Strip (FTS) test, and Mansonella, assessed by qPCR on dried blood spots (DBS).
• To use data from a. and b. to estimate sensitivity and sensitivity of the new tests in the Mozambican setting.
• To assess the usability of the novel tests by collecting data from the surveyors on their use and readability.
Methods
As part of the wider DISSECT research protocol, residents from two communities in the DISSECT study area were tested using an expanded diagnostic panel. All residents aged 5 years and older were eligible to participate. The diagnostics and samples collected for each individual were:
• Onchocerciasis screening: DDTD onchocerciasis RDT in the community; GADx onchocerciasis RDT in the community,60 ul whole blood for dried blood spot (DBS) for onchocerciasis SD bioline RDT screening in the lab.
• Mansonella screening: 60 ul whole blood for DBS to be used for Mansonella qPCR testing in the lab.
• Lymphatic filariasis screening: 75ul whole blood for lymphatic filariasis FTS test during the day, for anyone testing positive by FTS an additional 60ul night blood draw for DBS for LF qPCR.
Results discussion
In cases where there is no true gold standard diagnostic test, and no way to know who is truly infected or not, analyzing the performance of novel tests is difficult. Relative to the skin biopsy O-150 analysis, which is a definitive determinant of active infection, but with recognized limitations in sensitivity, the GADx test had 75.00% sensitivity and 77.52% specificity. DDTD recorded 64.29% sensitivity and 75% specificity when defining positivity as any line, but with the stricter criteria needing both lines the sensitivity is 7.14% and specificity 98.00%. However the WHO threshold for stopping MDA, and for OEM, make reference to Ov16 antibody prevalence, rather than skin snip positivity. The SD bioline RDT (lab) is one of the accepted methods of determining Ov16 prevalence. Relative to this test, the GADx had sensitivity of 82.14% and specificity of 98.18%. The DDTD had 77.78% sensitivity and 99.10 specificity.