Disease condition and impact on the patient: Dengue fever has a wide spectrum of clinical presentations, often with unpredictable clinical evolution and outcome. While most patients recover after a self-limiting, non-severe clinical course, a small proportion of cases progress to severe disease, characterized mainly by plasma leakage with or without haemorrhage. Intravenous rehydration is the therapy of choice, as it can reduce the fatality rate of severe cases to < 1%. Progression from non-severe to severe disease is difficult to define; however, appropriate treatment can prevent more severe clinical conditions. Does the test meet a medical need? Efficient, accurate diagnosis of dengue is of primary importance for clinical care (for early detection of severe cases, case confirmation and differential diagnosis from other infectious diseases), surveillance, outbreak control, pathogenesis, academic research, vaccine development and clinical trials. During the early stages of the disease, detection of antigens can be used to diagnose an infection, while, at the end of the acute phase of infection, serology is the method of choice. The choice of the assay for diagnosis depends on the time of sample collection and the purpose of testing (1). As for other Aedes-borne arboviruses, viraemia is present during the acute phase, and 90% of cases of primary and secondary dengue fever can be identified accurately from a single serum specimen collected during the first 10 days of illness, with DENV-1-4 real-time RT-PCR plus IgM ELISA or NS1 antigen ELISA (2, 3). Purposes of testing: In surveillance, the test is used to alert health authorities to possible emergence of an outbreak. Tests to identify the cause of an outbreak must be highly sensitive and specific in detecting DENV directly by isolation of the virus, its nucleic acid or its antigen in the acute phase of infection. Infection can also be diagnosed retrospectively from seroconversion of IgM or a four-times increase in IgG between the acute and convalescent values in serum samples collected > 14 days apart. A combination of IgM and either NAATs or antigen detection tests extends the window of detection of acute infection. The tests can also be used to assess the extent of an outbreak, inform control strategies and identify hotspots. High-throughput, ideally highly specific tests that can be used in various populations are required. In research, they are used to assess the impact of control interventions and improve understanding of the pathogen and its pathogenesis. How the test is used: There are many NAATs for DENV, which can be used with whole blood, sera or tissue specimens taken from patients during the acute phase of infection. NAAT assays can provide results the same or the next day for DENV in serum or plasma taken from patients in the acute phase of the infection. Depending on the set-up, the assay can be used at three levels of health systems: primary care centres, district centres and reference centres. A single test is sufficient if the sample is taken within the predefined time. As dengue fever is easily confused with non-dengue illnesses, particularly in non-epidemic situations, the DENV IVD can also be used as a differential test.

Prevalence: Dengue fever is the most rapidly spreading mosquito-borne viral disease in the world. Its incidence has increased 30 times over the past 50 years, with increasing geographical spread to new countries and, in the current decade, from urban to rural settings. An estimated 50 million cases of DENV infection occur annually, and approximately 2.5 billion people live in dengue-endemic countries. World Health Assembly resolution WHA55.17 in 2002 urged greater commitment to dengue fever by WHO and its Member States. Of particular significance is World Health Assembly resolution WHA58.3 on revision of the IHR in 2005, which included dengue fever as an example of a disease that may constitute a PHEIC, with implications for health security due to disruption and rapid epidemic spread beyond national borders. Socioeconomic impact: The global cost of dengue fever is estimated to be almost US$ 9 billion per year for prevention and control (4), and WHO estimated that more than 3 billion DALYs are lost annually from dengue illness.

Guidelines for patient care in the Region of the Americas (5).

Najioullah et al. (6) evaluated four commercial real-time RT-PCR kits: Simplexa™ dengue RT-PCR assay (Focus Diagnostics, USA), RealStar Dengue RT-PCR kit 1.0 (Altona Diagnostics, Germany), DENV general type real-time RT-PCR kit Liferiver™ (Shanghai ZJ Bio-Tech Co, China) and DENV 1-4 real-time RT-PCR kit (Genome Diagnostics Pvt, India). In three of the assays, amplification and detection were performed on the ABI Prism® 7500 (Applied Biosystems, France). For Simplexa, the 3M integrated cycler provided by Focus was used. The Liferiver™ kit was poorly sensitive in the initial panel of 40 positive samples, detecting only 40%, and was not evaluated further. The sensitivity of the other three assays was 85.2% for Geno-sen’, 83.3% for Realstar and 93.2% for Simplexa. Saengsawang et al. (7) evaluated two commercial real-time PCR assays for the detection of DENV infection, abTES DEN 5 quantitative PCR (abTES) (AITbiotech, Singapore) and the DETECT Two-step assay (innuDETECT; Analytik, Germany). Amplification and detection were done with the compact CFX96 real- time thermocycler (Bio-Rad Laboratories, Hercules, CA, USA). Positive results for DENV were found for 117 samples by nested RT-PCR and IgM/IgG ELISA. Serotypes were identified by nested RT-PCR. The abTES assay performed well, with an overall sensitivity of 97.4%, while the innuDETECT assay showed an overall sensitivity of only 44.4%. The eight control serum samples were negative in both assays, giving a specificity of 100%. The authors concluded that the abTES assay allows rapid diagnosis of DENV infection, which could be useful when urgent clinical care is needed.

If only a subset of patients is tested during outbreaks or endemic periods, for confirmation, the impact on budgets will be small.

Consent is required to obtain a blood sample. Dengue fever predominantly affects populations living in poverty, and access to high-quality diagnostics could reduce the burden and improve equity.