ABSTRACT
Introduction: The screening methods for determination of HIV infection have been developedfrom the first-generation to the fourth-generation assays. The fourth-generation assays are thecombination methods that can detect HIV-1, HIV-2 antibodies and HIV p24 antigen. In this study, e evaluate two fourth-generation assays, AxSym HIV Ag/Ab Combo (Enzyme-linkedimmunosorbent assay; ELISA, Abbott laboratories) and Cobas HIV Ag/Ab Combi (Electrochemiluminescenceimmunoassay; ECLIA, Roche diagnostics).Methods: Serum specimens of 64 patients received from routine laboratory for HIV testing and26 plasma samples from donors of Khon Kaen Hospital were tested for HIV infection using twofourth-generation assays and three anti-HIV screening assays. These consist of a third generation antibody assay (AxSym HIV 1/2 gO; ELISA), a gelatin particle agglutination test (GPA) and immunochromatiographic test (ICT). The validity of the two fourth-generation assays were evaluated in relation to sensitivity, specificity, predictive value and likelihood.Results: The AxSym HIV Ag/Ab Combo demonstrated high sensitivity (100%, 95% CI:100-100%) and low specificity (97.50%, 95% CI:93-100%) with 96.55% (95% CI:90-100%) and 100% (95% CI:100-100%) of PPV and NPV, respectively. Similarly, Cobas HIV Ag/Ab Combi showed high sensitivity (100%, 95% CI:100-100%) and low specificity (96.07%, 95% CI:91-100%) with 94.11%(95% CI:86-100%) and 100% (95% CI:100-100%) of PPV and NPV, respectively. The positivelikelihood ratio of AxSym HIV Ag/Ab Combo was 40 (95% CI:5.77-277.06%) and Cobas HIVAg/Ab Combi was 25 (95% CI:6.55-99.20%).Conclusions: The two fourth-generation assays have high sensitivity and low specificity. Therefore, individual diagnosis of HIV infection using the fourth-generation assays should be performed under good laboratory practices.
ABSTRACT
Avian influenza (Bird flu), an acute respiratory tract infection caused by influenza virus type A. Recently reported H5N1 flu virus strain may have been transmitted directly from birds to humans. The acute respiratory distress syndrome (ARDS) caused by avian influenza H5N1 viral infection has been one of the most important reasons for patient death. To control disease outbreaks and earlier patient treatment the rapid and accurate detection are the important factors. Recently, rapid test has been widely used as a tool for the screening of avian flu because it provides rapid detection. The aim of this work was to assess the performance and effectiveness of rapid test; Clearview Exact Influenza A\&B for detection of influenza A virus in nasopharygneal swab were collected from patients with influenza-like illness admitted in Khon Kaen Hospital by using RT-PCR as the reference method. The prevalences of Influenza A positive in 50 cases measured by rapid test and RT-PCR are 23.8% and 66.7%. The Sensitivity, Specificity, Positive predictive value, Negative predictive value and Prevalence are 83.33% (95%CI 51.5-91.9), 100% (95%CI 88.4-100), 100% (95%CI 69.1-100), 93.75% (95%CI 79.2-99.2) and 28.57% (95%CI 15.7-44.6) respectively. The finding that the sensitivity of rapid test was slightly low when compared with standard method RT-PCR. There may dependent on many factors including the method of specimen collection, the test method used, geographic location, and the disease prevalence in specific localities. In addition, the important properties of diagnostic tests that need to considered are analytical sensitivity and analytical specificity.
ABSTRACT
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.