Laboratory diagnostics of dengue fever: An emphasis on the role of commercial dengue virus nonstructural protein 1 antigen rapid test

Background/Purpose(s) In 2008, the Dengue NS1 Ag STRIP (Bio-Rad Laboratories, Marnes-la-Coquette, France) was introduced to routine dengue diagnostics in Taiwan, in addition to real-time reverse-transcription polymerase chain reaction (PCR), virus isolation, and capture immunoglobulin (Ig)M/IgG enzyme-linked immunosorbent assay (ELISA). This study aimed to evaluate the benefit of this assay and factors influencing the results of these diagnostic tests. Methods Retrospectively, the authors enrolled laboratory-confirmed adult dengue patients from July 2008 to January 2012 in a tertiary hospital. The sensitivities of each test alone and in combination were analyzed by the duration of illness (early stage: day 0-day 3 and late stage: day 4-day 8). The factors influencing sensitivity of the Dengue NS1 Ag STRIP were examined. Results There were 392 patients enrolled. The overall sensitivity of the Dengue NS1 Ag STRIP was 68.37% and PCR was 71.94%. With the assistance of the Dengue NS1 Ag STRIP, a diagnosis was made in 10.97% of patients without the need for second convalescent samples, and 4.34% more cases were detected. Independent factors for reduced Dengue NS1 Ag STRIP sensitivity were dengue virus (DENV) IgG seropositivity and a sample taken after the fifth day of illness. At the early stage, the PCR and the Dengue NS1 Ag STRIP combination had the highest sensitivity rate than other combinations. At the late stage, a combination of the Dengue NS1 Ag STRIP and capture IgM/IgG ELISA had better sensitivity rates. PCR and capture IgM/IgG ELISA in combination had sensitivity above 90% through the course of illness. Conclusion Dengue NS1 Ag STRIP is a useful tool for early dengue diagnosis. Its use can increase the diagnostic sensitivity and decrease the need of convalescent samples. Seeking treatment late (days postonset > 4) and DENV IgG seropositivity independently decrease the sensitivity of the Dengue NS1 Ag STRIP.