RESUMEN
Background: Dengue Hemorrhagic Fever is a disease caused by dengue viruses which are transmitted by Aedes aegypti mosquitoes. The disease causes mortality and morbidity in school children, and more recently in adults. Technology assisting clinical diagnosis has been on the rise and recent development of rapid immuno-chromatographic tests (ICT) that allow on-the-site identification of dengue specific antibodies are available. We evaluate a rapid ICT by PANBIO° that displays dengue specific IgM and IgG on paper strips and compare the results with a standard antibody-captured ELISA. Method: A set of plasma specimens from 66 patients admitted into Khon Kaen Hospital were tested blind using the ICT method. The specimens were from a group of dengue infection patients and a group of patients with other febrile illnesses recruited into a study as funded by the Thailand Tropical Diseases Research Program. The project documented the time of collection in relation to the day of fevers and also the immune status (as assessed by dengue IgM/IgG ELISA). Validity of the rapid test was analysed in relation to sensitivity, specificity, predictive value and likelihood ratio.Results: In the sera from patients classified as primary infection, dengue IgM (by ICT) was detected on day 5 (67%) and the detection rate increase on day 6 (75%) to day 7 (100%); but all the specimens on day 2 to day 4 were negative. In secondary dengue infection, dengue IgG (by ICT) was detected on day 3 (33%) and increased from day 4 (68%) to day 7 (88%); all specimens from day 2 were negative. Irrespective of immune classification, specimens collected during day 3 to day 8 of illness, the rapid test deliver moderate sensitivity (76.0%) and low specificity (53.8%) with 94.2% and 18.4% of PPV and NPV respectively; but if the data were analysed covering day 5 to day 8, the sensitivity and specificity were 86.8% and 33.3% respectively. The likelihood ratio was also summarised for the rapid test accuracy. The positive likelihood ratio of rapid test was 1.65 (when specimens from day 3-8 were used) and 1.30 (day 5-8).Conclusion: The rapid test gave positive results in dengue infected patients only after 3 days of fever with moderate sensitivity and low specificity. The test improved its performance in later days of fever. It is therefore recommended that the test should be used and interpreted together with the data of the length of pyrexia.