Diarrhegenic <i>Escherichia coli</i> Replaces <i>Shigella</i> sp. as the Predominant Bacteria Causing Childhood Diarrhea in Andaman and Nicobar Islands, India.

The Andaman and Nicobar Islands is an archipelago of more than 500 islands situated in the Bay of Bengal, about 1,200 km away from peninsular India (92° to 94°E longitude; 6° to 14°N latitude). The archipelago, a Union Territory of India, is inhabited by more than 350,000 people, including six aboriginal tribes and settlers from mainland India. Acute diarrhea is common among the children of Andaman Islands.1,2 Regional Medical Research Center has been monitoring its clinical, epidemiological, and microbiological aspects since 1994 through a hospital-based surveillance. Shigellosis, with an isolation rate of Shigella spp. varying from 10% to 30% had been the principal cause of bacterial diarrhea over the years.1,2 Species and serotype composition of Shigella isolates varied considerably over the years. Endemic infections had been mainly due to Shigella flexneri 2a whereas Shigella dysenteriae Type 1 was responsible for occasional epidemics.3 Among the four serogroups of Shigella, S. flexneri 2a was found to be predominant in the island since 1994, which was replaced by Shigella sonnei during 2002-2005.4 During 2003-2009, multidrug-resistant strains started to emerge.3 The Earthquake and Great Asian Tsunami in 2004 not only altered the topography of the islands, but also resulted in the massive rebuilding of infrastructure, changes in administration policies, social and demographic characteristics of the residents, and increase in the number of tourists. Revamped water supply and sanitation systems with changes in infrastructure were cited as reasons for substantial decrease in the number of diarrheal cases.5 Although screening for diarrheagenic Escherichia coli (DEC) was included in the surveillance from the year 2008, infection due to DEC remained significantly lower than that due to Shigella till 2011. During 2011-2013, the frequency of infections due to DEC became almost equal to that of Shigella, and in 2014, it emerged as the predominant bacterial cause of acute childhood diarrhea (Figure 1). The DNA templates were subjected to multiplex polymerase chain reaction (PCR) using specific primers described previously.6 The cycling condition was 96°C for 4 minutes, 35 cycles of 95°C for 20 seconds, 57.5°C for 20 seconds, 72°C for 1 minute, with a final extension at 72°C for 7 minutes following Panchalingam et al.6 with slight modifications. Positive and negative controls were used with each PCR set up. Strains known to possess the target genes were used as the positive control and sterile distilled water was used as the negative control. Control strains were kindly provided by National Institute of Cholera and Enteric diseases, Calcutta.