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Combining RDTs Determines Dengue Immune Status

By LabMedica International staff writers
Posted on 18 May 2022
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Image: The Panbio Dengue IgM Capture ELISA is used to detect IgM antibodies to dengue antigen in serum as an aid to clinical laboratory diagnosis of patients with clinical symptoms consistent with dengue fever (Photo courtesy of Abbott)
Image: The Panbio Dengue IgM Capture ELISA is used to detect IgM antibodies to dengue antigen in serum as an aid to clinical laboratory diagnosis of patients with clinical symptoms consistent with dengue fever (Photo courtesy of Abbott)

Dengue is an emerging arboviral infectious disease (DENV), transmitted through the bite of an Aedes mosquito that burdens much of the urbanized tropical and subtropical world. Current dengue diagnostics are primarily concerned with capturing active infections, thus no such method exists for determining primary or post-primary DENV infections, at the point of care.

By assaying for changes in both DENV IgM and IgG antibodies, a rise in IgM titers coupled with high and low convalescent IgM: IgG ratios indicate active primary and secondary infections, respectively. Scientists have investigated how combining different rapid diagnostic tests (RDTs) can be used to accurately determine the primary and post-primary DENV immune status of reporting patients during diagnosis.

A team of scientist specializing in tropical medicine and led by those at the London School of Hygiene and Tropical Medicine (London, UK) collected serum from cross-sectional surveys of acute suspected dengue patients in Indonesia (N:200) and Vietnam (N: 1,217) and were assayed using dengue laboratory assays and RDTs. The team used logistic regression modeling, and determined the probability of being DENV NS1, IgM and IgG RDT positive according to corresponding laboratory viremia, IgM and IgG ELISA metrics.

Samples were assayed for the presence of DENV1-4 viremia using the CDC fourplex, real-time polymerase chain reaction (RT-PCR) test. The presence of DENV IgM and IgG antibodies was performed using Panbio capture ELISAs (Abbott, East Princeton, NJ, USA). Assays detect IgM/G antibodies specific to all serotypes and provide plate-calibrated titer outputs termed ‘panbio units’. Another RDTs used in the study were DENV NS1 RDT (Bio-Rad, Hercules, CA ,USA). Among samples from Indonesia, patient serum samples were tested for DENV NS1 using both Abbott’s NS1 capture ELISAs) and NS1 RDTs (SD Biosensor, Yeongtong-gu, Republic of Korea).

The investigators reported that combining NS1, IgM and IgG RDTs captured 94.6% (52/55) and 95.4% (104/109) of laboratory-confirmed primary and post-primary DENV cases, respectively, during the first 5 days of fever. Laboratory test predicted, and actual, RDT outcomes had high agreement (79.5% (159/200)). Among patients from the Philippines, different combinations of estimated RDT outcomes were indicative of post-primary and primary immune status. Overall, IgG RDT positive results were confirmatory of post-primary infections. In contrast, IgG RDT negative results were suggestive of both primary and post-primary infections on days 1–2 of fever, yet were confirmatory of primary infections on days 3–5 of fever.

The authors concluded that they had described methods for estimating the primary and post-primary immune status of dengue patients at the point of care, using a combination of simple-to-use rapid diagnostic tests. Using all three NS1, IgM and IgG RDTs, they demonstrated how at certain stages of infection health care workers and surveillance operations could confidently determine types of dengue infections. The study was published on May 4, 2022 in the journal PLOS Neglected Tropical Diseases.

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