Evaluation of Commercially Available Anti–Dengue Virus Immunoglobulin M Tests

Anti–dengue virus immunoglobulin M kits were evaluated. Test sensitivities were 21%–99% and specificities were 77%–98% compared with reference ELISAs. False-positive results were found for patients with malaria or past dengue infections. Three ELISAs showing strong agreement with reference ELISAs will be included in the World Health Organization Bulk Procurement Scheme.

. Positive samples were selected based on optical density (OD) and were weighted toward low and medium ODs. Negative control samples included serum samples from healthy persons in areas where dengue is not endemic and from patients with other fl avivirus infections, febrile illness of other causes, or systemic conditions. Results were con-fi rmed as negative for IgM antibodies against DENV by using predetermined reference standards. Additionally, 20 anti-DENV IgM-negative specimens were obtained from SeraCare Diagnostics (Milford, MA, USA). Panel specimens were coded, heat-inactivated, aliquoted, and lyophilized; 1 aliquot was retested by the reference laboratories after reconstitution.
Letters of interest and the evaluation protocol were sent to 20 dengue kit manufacturers. Six companies agreed to participate and provided 4 rapid diagnostic tests (RDTs) and 5 microplate ELISAs. Test characteristics are summarized in Table 2. Price per test ranged from US $3 to $15.

Conclusions
This laboratory-based evaluation used a serum panel to determine the ability of 9 commercially available anti- DENV IgM tests to detect low levels of IgM and to determine specifi city against pathogens that often cocirculate with DENV. Field trials are needed to determine the performance and utility of these tests in a local context. Of the 5 ELISA kits evaluated, 3 (Focus, Panbio, and Standard) showed strong agreement with reference standard results and were consistent across all evaluation sites. Of concern are false-positive results shown by some tests on sera that were anti-DENV IgM negative but malaria positive, anti-DENV IgG positive, or rheumatoid factor positive. The laboratory at Mahidol University also tested the kits against 12 serum samples from patients with leptospirosis. The Panbio ELISA showed cross-reactivity with 58% of these samples, and the Focus ELISA showed crossreactivity with 25%. Further studies are needed to elucidate the cause of this cross-reactivity.
Technicians were asked to score tests' user-friendliness. All RDTs scored higher than ELISAs, and the Panbio RDT scored highest.
Limitations of anti-DENV IgM tests include their inability to identify the infecting DENV type and potential antibody cross-reactivity with other fl aviviruses (11,12). However, cross-reactivity to related viruses did not appear to be a problem with these tests. IgM tests can be useful for surveillance and support diagnosis of DENV infection in conjunction with clinical symptoms, medical history, and other epidemiologic information (13). Because IgM persists for >60 days, IgM assays should not be used in dengue-endemic countries as confi rmatory tests for current illness. Presence of IgM indicates that a dengue infection has occurred in the past 2-3 months.
This evaluation has several limitations. Test performance was compared with reference laboratory assay results, which may be less sensitive than commercial assays, leading to some results being misclassifi ed as false positive. Specifi city of these tests may be higher in a fi eld setting than in this evaluation because not all potential causes of false-positive results would be present. The panel consisted of a high proportion of specimens from persons with secondary DENV infections. Thus, the panel was weighted toward lower anti-DENV IgM levels. However, this feature refl ects the situation in most dengue-endemic countries. Thus, tests that performed well against this panel could be expected to perform well in these diagnostic settings. We could not comprehensively evaluate whether the kits could detect primary infections with all 4 DENVs because all DENV types were not represented in the panel.
Data from this evaluation have been provided to the manufacturers and WHO member states. On the basis of these results, ELISAs from Focus, Panbio, and Standard Diagnostics will be included in the WHO Bulk Procurement Scheme. Technical discussions are ongoing to determine how tests might be improved to accelerate availability of useful methods for dengue case management, surveillance, and disease control.