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.
ABSTRACT
Background: Mixed-species malaria infections examined by microscopy of Giemsa-stained thick blood films (GS-TBF) during 1996-2007 in Thailand were 0.3-0.5. However, there were reports of higher mixed-species infection rates detected by polymerase chain reaction (PCR) method. This study was conducted in order to ascertain the relative frequency of mixed-species malaria infection and possible determinants in top 10 malaria high transmission provinces of Thailand. Methods: This study was a survey of mixed Plasmodium species incidence in the top 10 malaria transmission provinces of Thailand. A total of 836 malaria patients were examined. The number of samples in each province was proportionate to the number of malaria patients in that province. A real-time PCR based on SYBR Green I detection system was used to detect and differentiate Plasmodium species. Results: Preliminary results from GS-TBF examined by the microscopists at the malaria clinics in the selected areas showed that 380 (45.5%) of 836 patients were infected by Plasmodium falciparum; 450 (53.8%), 2 (0.2%) and 4 (0.5%) were infected by P. vivax, P. malariae and mixed P. falciparum and P. vivax, respectively. Real-time PCR results of the corresponding samples from filter papers showed that 353 (42.2%) were infected by Plasmodium falciparum; 446 (53.4%), 1 (0.1%), 2 (0.2%), 32 (3.8%), 1 (0.1%) and 1 (0.1%) were infected by P. vivax, P. malariae, P. ovale, mixed P. falciparum and P. vivax, mixed P. falciparum and P. malariae and mixed P. vivax and P. ovale, respectively. Conclusion: Mixed-infection rates detected by real-time PCR were 8.48 (4.07/0.48) times higher than those detected by GS-TBS. Demographic factors including age, sex, occupation, place where contracted the disease and recurrence of the infection were not different between the groups with mono-species infection and mixed-species infection.