ABSTRACT
To determine the proportion of dengue non-structural protein 1 (NS1) positives among laboratory confirmed dengue IgM negative patients. Methods: Data for 1 732 samples received from January to October 2017 at the Virus Research and Diagnostic Laboratory (VRDL) for dengue diagnosis were downloaded from the National Institute of Epidemiology server. Samples that were previously reported as IgM negative for dengue diagnosis were identified and their NS1 status was determined using ELISA. Thus, 'missed out' NS1 positives were correlated with the duration of illness. Furthermore, an epidemic curve for the study period was constructed. The increase in positivity rate within and between the months was compared by McNemar's and Pearson's chi-square test, respectively. Results: The reported IgM-negatives were 813, of which, 22.5% (183) were retrospectively positive for NS1 antigen. The addition of NS1 positives revealed by this study has raised the reported positivity across the months that ranged from 8.1% to 29.6%. By analyzing the dengue positives per month and the epidemic curve, the period between January and September, 2017 was identified as non-epidemic while the epidemic started from the month of October, 2017. Conclusions: Acute dengue infection is widely confirmed by detecting NS1 antigen in serum. Missing out of NS1 positives happen due to shortened window period and such cases act as reservoir for further viral transmission. Hence, this study highly emphasizes performing all three tests for dengue diagnosis that warrants the accurate dengue proportion in India.
ABSTRACT
To determine the proportion of dengue non-structural protein 1 (NS1) positives among laboratory confirmed dengue IgM negative patients. Methods: Data for 1 732 samples received from January to October 2017 at the Virus Research and Diagnostic Laboratory (VRDL) for dengue diagnosis were downloaded from the National Institute of Epidemiology server. Samples that were previously reported as IgM negative for dengue diagnosis were identified and their NS1 status was determined using ELISA. Thus, 'missed out' NS1 positives were correlated with the duration of illness. Furthermore, an epidemic curve for the study period was constructed. The increase in positivity rate within and between the months was compared by McNemar's and Pearson's chi-square test, respectively. Results: The reported IgM-negatives were 813, of which, 22.5% (183) were retrospectively positive for NS1 antigen. The addition of NS1 positives revealed by this study has raised the reported positivity across the months that ranged from 8.1% to 29.6%. By analyzing the dengue positives per month and the epidemic curve, the period between January and September, 2017 was identified as non-epidemic while the epidemic started from the month of October, 2017. Conclusions: Acute dengue infection is widely confirmed by detecting NS1 antigen in serum. Missing out of NS1 positives happen due to shortened window period and such cases act as reservoir for further viral transmission. Hence, this study highly emphasizes performing all three tests for dengue diagnosis that warrants the accurate dengue proportion in India.
ABSTRACT
The present work evaluated the diagnostic accuracy of detection of Dengue NS1 antigen employing two NS1 assays, an immunochromatographic assay and ELISA, in the diagnostic routine of Public Health laboratories. The results obtained with NS1 assay were compared with virus isolation and, in a subpopulation of cases, they were compared with the IgM-ELISA results obtained with convalescent samples. A total of 2,321 sera samples were analyzed by one of two NS1 techniques from March to October 2009. The samples were divided into five groups: groups I, II and III included samples tested by NS1 and virus isolation, and groups IV and V included patients with a first sample tested by NS1 and a second sample tested by IgM-ELISA. Sensitivity, specificity, positive and negative predictive values, Kappa Index and Kappa Concordance were calculated. The results showed that NS1 testing in groups I, II and III had high sensitivity (98.0 percent, 99.5 percent and 99.3 percent), and predictive values and Kappa index between 0.9 - 1.0. Groups IV and V only had Kappa Concordance calculated, since the samples were analyzed according to the presence of NS1 antigen or IgM antibody. Concordance of 92.1 percent was observed when comparing the results of NS1-negative samples with IgM-ELISA. Based on the findings, it is possible to suggest that the tests for NS1 detection may be important tools for monitoring the introduction and spread of Dengue serotypes.
Esse estudo avaliou a acurácia do diagnóstico por detecção do antígeno NS1 do vírus Dengue empregando-se ensaios em dois formatos, imunocromatográfico e ELISA, na rotina diagnóstica dos laboratórios de Saúde Pública. Compararam-se os resultados de NS1 com os resultados de isolamento viral e, em parte dos casos, foi feita a comparação com os resultados de IgM-ELISA, obtidos nas segundas amostras. Um total de 2.321 amostras de soros, obtidas no período de março a outubro de 2009, foram analisadas por uma das duas técnicas NS1. As amostras foram divididas em cinco grupos: I, II e III, que incluíram amostras analisadas por testes NS1 e por isolamento de vírus. Os grupos IV e V incluíram pacientes com a primeira amostra processada por NS1 e segunda por IgM-ELISA. Foram analisadas sensibilidade, especificidade, valor preditivo positivo e negativo, concordância e índice Kappa. Os resultados mostraram que os grupos I, II e III apresentaram alta sensibilidade (98,0 por cento, 99,5 por cento e 99,3 por cento), valores preditivos e índice Kappa entre 0,9 - 1,0. Nos grupos IV e V, apenas concordância foi calculada, dado que as amostras foram analisadas quanto à presença de antígeno NS1 ou de anticorpos IgM. Comparando-se os resultados negativos de NS1 com IgM-ELISA houve 92,1 por cento de concordância. Com base nas constatações feitas, é possível sugerir que a detecção de NS1 pode ser importante ferramenta para monitorar a introdução e disseminação dos sorotipos de Dengue.