Abstract
Shigellosis, caused by Shigella species, is a major public health problem in Bangladesh. To determine the prevalence and distribution of different Shigella species, we analyzed 10,827 Shigella isolates from patients between 2001 and 2011. S. flexneri was the predominant species isolated throughout the period. However, the prevalence of S. flexneri decreased from 65.7% in 2001 to 47% in 2011, whereas the prevalence of S. sonnei increased from 7.2% in 2001 to 25% in 2011. S. boydii and S. dysenteriae accounted for 17.3% and 7.7% of the isolates respectively throughout the period. Of 200 randomly selected S. sonnei isolates for extensive characterization, biotype g strains were predominant (95%) followed by biotype a (5%). Resistance to commonly used antibiotics including trimethoprim-sulfamethoxazole, nalidixic acid, ciprofloxacin, mecillinam and ampicillin was 89.5%, 86.5%, 17%, 10.5%, and 9.5%, respectively. All isolates were susceptible to ceftriaxone, cefotaxime, ceftazidime and imipenem. Ninety-eight percent of the strains had integrons belonging to class 1, 2 or both. The class 1 integron contained only dfrA5 gene, whereas among class 2 integron, 16% contained dhfrAI-sat1-aadA1-orfX gene cassettes and 84% harbored dhfrA1-sat2 gene cassettes. Plasmids of ∼5, ∼1.8 and ∼1.4 MDa in size were found in 92% of the strains, whereas only 33% of the strains carried the 120 MDa plasmid. PFGE analysis showed that strains having different integron patterns belonged to different clusters. These results show a changing trend in the prevalence of Shigella species with the emergence of multidrug resistant S. sonnei. Although S. flexneri continues to be the predominant species albeit with reduced prevalence, S. sonnei has emerged as the second most prevalent species replacing the earlier dominance by S. boydii and S. dysenteriae in Bangladesh.
Highlights
Bacillary dysentery such as shigellosis is endemic throughout the world, and is one of the major causes of morbidity and mortality, especially among children,5 years of age in many developing countries including Bangladesh [1,2]
Epidemiologic Studies Of 10,827 strains of Shigella species isolated from patients of all ages between 2001 and 2011, S. flexneri was the dominant species throughout the study period, but the decreasing tendency of predominance was observed starting from 65.7% (824/1252) in 2001 to 47% (306/650) in 2011
The prevalence of S. dysenteriae came down from 10.7% (135/1252) in 2001 to 9% (60/650) in 2011, whereas S. sonnei increased from 7.2% (90/1252) in 2001 to 25% (162/650) in 2011
Summary
Bacillary dysentery such as shigellosis is endemic throughout the world, and is one of the major causes of morbidity and mortality, especially among children ,5 years of age in many developing countries including Bangladesh [1,2]. Shigellosis is caused by any one of the four species of Shigella: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei and outbreaks caused by Shigella infection are difficult to control due to their low infectious dose [3,4]. Every year there are about 165 million cases of Shigella infection and 1.1 million Shigella-related deaths. The majority of these cases occur in developing countries [5]. S. flexneri was the predominant serogroup (55%) followed by S. dysenteriae (19%), S. boydii (13%) and S. sonnei (7%) [8]
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