Trends in antimicrobial resistance in Shigella species in Karachi, Pakistan

Background: Shigellosis is a common cause of morbidity, especially in the very young and old, in developing countries. The disease is treated with antibiotics. Surveillance of antimicrobial resistance trends is essential owing to the global emergence of antimicrobial resistance. Methodology: The study involved 1,573 isolates of Shigella species (1996-2007) that were analyzed for trends in antimicrobial resistance. Results: The majority of the specimens (1046; 66.5%) were from the pediatric population, and of these 887 (84.8%) were under 5 years of age (p = 0.001). S. flexineri was the most frequent species (54.5%) isolated. Isolation of S. sonnei increased from 15.4 % (1996) to 39% (2007) (p = 0.001). Although none of the isolates was found sensitive to all the antibiotics tested, 58% (n =9 07) were resistant to ampicillin and 85% (n = 1,338) were resistant to trimethoprim-sulfamethoxazole (TMP-SMX). Out of a total of 198 (12.6%) nalidixic acid resistant isolates, 6 (3.0%) were also resistant to ofloxacin. Overall 1.7 % of isolates were resistant to ofloxacin, 2.4% to ceftriaxone and 2.3% were resistant to combination of ampicillin, nalidixic acid and TMP-SMX. Conclusion: Ofloxacin is still an effective drug for treatment of acute shigellosis in Pakistan. Emergence of resistance to ceftriaxone in Shigella may have grave implications in treatment of severe shigellosis in very young patients.