ABSTRACT
Background: Laboratory diagnosis of dengue infection is complicated by the variability of either virus, antigen or antibody appearance in blood circulation. Patients came to the hospital at different time intervals after the onset of fever. This resulted in problems in the selection of appropriate laboratory tests. Objective: To determine the appropriate laboratory assays for the diagnosis of dengue infection at a general hospital in Southern Thailand. Methods: Serum samples were obtained from 175 dengue-suspected patients attending Nakhon Si Thammarat Provincial Hospital, in Southern Thailand during the period January-September 2006. Dengue infected patients were classified as having clinical symptoms according to the WHO criteria for dengue infection combined with positive ELISA test results for IgM and/or IgG antibodies for dengue virus. All were assayed for dengue viral infection by real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR), Platelia Dengue NS1 Ag test (NS1-Ag), Dengue IgM Capture ELISA (ELISA-IgM), Dengue Indirect IgG ELISA (ELISA-IgG) and Dengue Duo IgM and IgG rapid strip test (RST). Results: One hundred of the 175 dengue suspected cases were diagnosed as having dengue viral infection. Thirty-eight cases (22%) were positive by NS1-Ag test, 36 (21%) by real-time RT-PCR, 41 (23%) by RST, 74 (42%) by ELISA-IgM and 88 (50%) by ELISA-IgG. Among the 100 positive cases, 40 cases (40%) were determined as primary infection and 60 cases (60%) as secondary infection on the basis of the variability of specific IgG and IgM levels in patient serum. The NS1-Ag test kit, real-time RT-PCR and RST detected more positive cases in primary infected patients compared to secondary infected patients (p \< 0.0001). With ELISA-IgG when combined with NS1-Ag, RT-PCR or ELISA-IgM, 88, 89 and 96% of the cases could be detected. Three combinations of ELISA-IgG, ELISA-IgM with NS1-Ag or RT-PCR resulted in 99 and 100 % positive cases. Conclusion: A combination of ELISA-IgG, ELISA-IgM with NS1 Ag test was appropriate for laboratory diagnosis of dengue infection at the hospital where equipment for running ELISA tests was available.