Performance of indirect immunofluorescence assay, immunochromatography assay and reverse transcription-polymerase chain reaction for detecting human respiratory syncytial virus in nasopharyngeal aspirate samples

Comparison of the use of indirect immunofluorescence assay (IFA), immunochromatography assay (ICA-BD) and reverse transcription-polymerase chain reaction (RT-PCR) for detecting human respiratory syncytial virus (HRSV) in 306 nasopharyngeal aspirates samples (NPA) was performed in order to assess their analytical performance. By comparing the results obtained using ICA-BD with those using IFA, we found relative indices of 85.0 percent for sensitivity and 91.2 percent for specificity, and the positive (PPV) and negative (NPV) predictive values were 85.0 percent and 91.2 percent, respectively. The relative indices for sensitivity and specificity as well as the PPV and NPV for RT-PCR were 98.0 percent, 89.0 percent, 84.0 percent and 99.0 percent, respectively, when compared to the results of IFA. In addition, comparison of the results of ICA-BD and those of RT-PCR yielded relative indices of 79.5 percent for sensitivity and 95.4 percent for specificity, as well as PPV and NPV of 92.9 percent and 86.0 percent, respectively. Although RT-PCR has shown the best performance, the substantial agreement between the ICA-BD and IFA results suggests that ICA-BD, also in addition to being a rapid and facile assay, could be suitable as an alternative diagnostic screening for HRSV infection in children.

Deteccao de antigenos bacterianos em pneumonia aguda: metodos de preparacao das amostras de urina, soro e liquido pleural para os testes de imunodiagnostico / Detection of bacterial antigens in acute pneumonia: methods of preparing the urine, serum and pleural fluid samples for immunodiagnostic assays

Foi desenvolvido um metodo de precipitacao de antigenos polissacaridicos de S. pneumoniae e H influenzae tipo b na urina, atraves do tratamento com uma solucao de etnol-acetona 1:1 seguido de um tratamento a quente com EDTA 0,1M. Foram empregadas as tecnicas de contra-imunoeletroforese e latex aglutinacao para a deteccao de antigenos polissacarideos em amostras pareadas de urina e soro e ainda de liquido pleural, de criancas com diagnostico clinico e radiologico de pneumonia aguda. Contra-imunoeletroforese e latex aglutinacao apresentaram melhores indices de sensibilidade em urina do que em soro e tiveram otimo desempenho tanto para urina de volume inicial relativamente pequeno como de grande volume, colhidas antes ou durante os primeiros dias de antibioticoterapia. Os resultados obtidos em contra-imunoeletroforese e latex aglutinacao mostraram que a solucao etanol-acetona 1:1 fornece melhor rendimento na precipitacao de antigeno polissacaridico enquanto que o aquecimento com EDTA diminui a probabilidade de ocorrencia de resultados falso-positivos e de reatividade cruzada entre S. pneumoniae e H. influenzae tipo b. A urina mostrou-se como importante meio de deteccao de antigenos bacterianos no diagnostico de pneumonia bacteriana aguda, principalmente se a antibioticoterapia previa obstrui o crescimento bacteriano nos meios de cultura.

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) for Chagas'disease serodiagnosis

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) was standardized and evaluated for the diagnosis of Chagas'disease in comparison with the conventional serological tests indirect immunofluorescence (IFI), passive hemagglutination (PHA) and complement fixation (CF). A total of 236 serum samples positive and negative for the serodiagnosis of Chagas'disease were studied. The group included 50 serum samples serologically positive for leishmaniasis and 36 positive for malaria. The best diagnostic performance of DIG-ELISA was observed when serum samples were diluted to 1:8 and a diameter of zero mm (no color) was taken as the cut-off. Under these conditions, the relative indices of sensitivity, specificity and agreement were 100%. High positive correlation coeficients were obtained between DIG-ELISA and IFI (r1=0.9010), PHA (r2=0.8943) and CF (r3=0.8269). We conclude that DIG-ELISA provides an alternative technique for screening chagasic infections, as well as for seroepidemiological surveys mainly because it is simple, easy to carry out and does not require expensive equipment