Introduction: Shigellosis, a severe diarrheal disease caused by Shigella associated with high morbidity and mortality in both developed and developing countries especially in Bangladesh. Recently, S. sonnei, the predominant serotype in developed countries, becoming predominant in developing countries replacing S. flexneri. Global burden estimates >160 million cases yearly. The aim of this study was to monitor the prevalence of Shigella specific phages among different water sources at different time and estimate actual disease burden due to Shigella infection.

Methods: During February 2006-January 2007; July 2014-December 2015, 180 water samples were collected from 16 different sites of 4 sources (rivers, lakes, canals and ponds) in Dhaka, Bangladesh to isolate Shigella specific phages and detect Shigella using standard microbiological and molecular methods. To test susceptibility of 142 phages, 57 different serotypes of Shigella including atypical and new variants were used. PCR for ipaH was done to detect Shigella.

Results: Highest serotype diversity of Shigella phages was found in canals followed by rivers, lakes and ponds. Most of the phages isolated during 2006-07 lysed mostly all serotypes among all species and very few phages found, lysed only serotypes of S. flexneri. However, in 2014 and 2015 only a few phages found which lysed at that pattern rather mostly lysed S. sonnei and predominant serotypes of S. flexneri with other serotypes and only few serotypes of S. boydi and S. dysenteriae. Our Dhaka Hospital data showed higher isolation of S. flexneri and S. sonnei from patients in 2014 and 2015 and lower isolation of S. boydi and S. dysenteriae compared to 2006. Water samples were positive for ipaH (17%), marker for detecting Shigella.

Conclusion: Detection of Shigella specific phages can be used as good indicator for monitoring prevalence of Shigella in environment and may provide new insights regarding the epidemiology of Shigella infection.