Date Published: January 27, 2017
Publisher: Public Library of Science
Author(s): Onanong Sengvilaipaseuth, Koukeo Phommasone, Xavier de Lamballerie, Manivanh Vongsouvath, Ooyanong Phonemixay, Stuart D. Blacksell, Mayfong Mayxay, Sommay Keomany, Phoutthalavanh Souvannasing, Paul N. Newton, Audrey Dubot-Pérès, Ana Paula Arez.
The Dengue Duo Rapid Diagnostic Test (SD Dengue RDT) has good specificity and sensitivity for dengue diagnosis in rural tropical areas. In a previous study, using four control sera, we demonstrated that that the diagnostic accuracy of these RDTs remains stable after long-term storage at high temperatures. We extended this study by testing sera from 119 febrile patients collected between July-November 2012 at Salavan Provincial Hospital (southern Laos) with RDTs stored for 6 months at 4°C, 35° and in a hut (miniature traditional house) at Lao ambient temperatures. The dengue NS1 antigen results from RDTs stored at 35°C and in the hut demonstrated 100% agreement with those stored at 4°C. However, lower positive percent agreements, with broad 95%CI, were observed for the tests: IgM, 60% (14.7–94.7) and 40% (5.3–85.3) for RDTs store at 35°C and in the hut, compared to those stored at 4°C, respectively. This study strenghtens the evidence of the robustness of the NS1 antigen detection RDT for the diagnosis of dengue after storage at tropical temperatures.
Imunochromatographic-based rapid diagnostic tests (RDTs) have multiple advantages, including providing results in less than 1 hour after sample collection, that can be performed at the patient’s bedside using a relative small volume of blood requiring limited technical skill to perform. This is especially relevant to low -resource countries where there is limited access to laboratory facilities. Over 2.5 billion people, nearly half of the world’s population, are now at risk of contracting dengue, and 70% of those live in southeast Asia and the western Pacific [1,2]. The SD Bioline Dengue Duo RDT (SD Dengue RDT, Standard Diagnostics, Alere, Waltham, Massachusetts, USA) has previously demonstrated greater than 80% sensitivity and specificity [3–7], for acute dengue diagnosis. The RDTs permit the concomitant detection of a dengue-specific antigen, NS1, on the left side cassette, and anti-dengue antibodies, IgM and IgG, on the right-side cassette. Therefore, this is a promising alternative for dengue diagnosis in Laos, and elsewhere in rural Asia [8–11]. However, the conditions of its use and storage in the field do not meet the standard of the laboratories where RDT evaluations are usually conducted. This is especially true during hot and rainy seasons when the storage temperature of the RDT storage may exceed the maximum temperature recommended by the manufacturer (30°C).
Comparisons of results obtained using RDTs stored in the different conditions are presented in Table 1 (results for individual patients are provided in supporting information S1 Table). Using the reference RDTs, stored at 4°C, 36 samples were positive for NS1 antigen, five for IgM and ten for IgG. Two samples gave equivocal results for IgG.
In this study 119 sera tested from suspected-dengue patients from a southern Lao rural provincial hospital were tested using RDTs stored at different temperatures for 6 months.