Early diagnosis of shigella infection -using novel enzyme apyrase.
Author(s): Saraswathy* M. P., Deepa R., Jayalakshmi G., Sankari K., Sripriya C. S.
Identification of Shigella, a major etiological agent in acute diarrhoeal disease in children, is based on virulence testing on animals or expensive molecular methods. This study aims to evaluate an alternative test, an apyrase based colorimetric assay as a screening test for early diagnosis of Shigella in children with diarrhoea. Materials and Methods: A total of 195 stool samples from children with acute diarrhoea (n=145) and from control group without diarrhoea (n=50) were subjected to stool culture and the colorimetric assay to detect the presence of the enzyme apyrase. Non lactose fermenting and late lactose fermenting colonies were subjected to polymerase chain reaction for the apy gene. Sereny’s test was done for all apy gene positive isolates. The two sample binomial proportion test was used to find the significance of apyrase positivity between the study and control group. PCR was taken as the gold standard and the sensitivity, specificity, predictive accuracy of the colorimetric assay calculated. Results: Among the bacterial isolates, the number of Shigella isolates was 8 (5.5 %) in the study group and none was in the control group (n=50). The colorimetric assay was positive in 11 stool samples (7.58%) in the study group. The colorimetric assay had 100% sensitivity, 98% specificity, 72% Positive predictive value, 100% negative predictive value and an accuracy of 98%. There was 2% false positivity and no false negativity. Conclusion: This study indicates that the colorimetric assay can be adopted for early diagnosis of Shigella from stool samples.
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