Changing Emergence of Shigella Sero-Groups in Bangladesh: Observation from Four Different Diarrheal Disease Hospitals

Background: Shigellosis continues to be a public health challenge for developing countries, including Bangladesh. The aim of the study is to demonstrate recent changes in Shigella sero-groups and their geographical diversity. Methods: Data were extracted from data archive of four diarrheal disease surveillance systems. A 2% sub sample from urban Dhaka Hospital (2008-2011; n = 10,650), and 10% from urban Mirpur Treatment Centre (2009-2011; n = 3,585), were enrolled systematically; whereas, all patients coming from the Health and Demographic Surveillance System area in rural Matlab (2008-2011; n = 6,399) and rural Mirzapur (2010-2011; n = 2,812) were included irrespective of age, sex, and disease severity. A fresh stool specimen was collected for identification of Shigella spp. Of them, 315 (3%) were positive for Shigella in Dhaka, 490 (8%) from Matlab, 109 (3%) from Mirpur and 369 (13%) from Mirzapur and considered as analyzable sample size. Results: Among all Shigella isolates regardless of age, significant decreases in percentage of S. flexneri over time was observed in Mirpur (55 -> 29%; p value of chi(2)-for trend = 0.019) and Mirzapur (59 -> 47%; p = 0.025). A non-significant decrease was also seen in Dhaka (58 -> 48%), while in Matlab there was a non-significant increase (73 -> 81%). Similar patterns were observed among under-5 children at all sites. Emergence of S. sonnei was found in Dhaka (8 -> 25%; p<0.001) and Mirpur (10 -> 33%; p = 0.015), whereas it decreased in Mirzapur (32 -> 23%; p = 0.056). The emergence of S. boydii was seen in all ages in Mirzapur [(3 -> 28%; p<0.001); (3 -> 27%; p<0.001)]. On the other hand, we saw non-significant percent reductions in S. boydii in Dhaka [overall (25 -> 16%); under-5 (16 -> 9%)]. Decreasing rates of Shigella dysenteriae were observed in Matlab, Mirpur and Mirzapur; whereas, in Dhaka it remained unchanged. Conclusion and Significance: Emergence of S. sonnei and S. boydii as important infectious diarrhea etiologies and variations in geographical diversity underscore the need for monitoring, with possible implications for vaccine development.