Frequency of isolation of shigella serogroups/serotypes and their antimicrobial susceptibility pattern in children from slum areas in Karachi.

OBJECTIVES To assess the frequency of serogroups and serotypes, as well as the antimicrobial susceptibility pattern of Shigella species isolated from known cases of diarrhoea and dysentery from Karachi, Pakistan. METHODS A cross-sectional study was conducted between January 2002 and March 2003 at Aga Khan University on stool samples received from children with diarrhoea and dysentery from four low socio-economic areas (Sultanabad, Rehri Goth, Hijrat and Sherpao colony) of Karachi. Stool samples yielding growth of Shigella species, were further identified for serotypes by slide agglutination. Antibiotics susceptibility was performed by Kirby Bauer disk diffusion method. RESULTS Out of 4688 stool samples received, 193 (4.1%) were positive for Shigella species. Shigella flexneri was the predominant serogroup (58%) followed by Shigella sonnei (16%), Shigella boydii (15%) and Shigella dysentriae being the least common (11%). A number of serotypes were isolated in each serogroup, 8 serotypes in S. flexneri, 8 serotypes in S. dysenteriae, 9 serotypes in S. boydii, and Phase 1 & 2 were found in S. sonnei. 17% isolates remained non-serotypeable. All isolates were susceptible to Ofloxacin and Ceftriaxone, high rate of resistance was observed in Cotrimoxazole (87.75%) and Ampicillin (55.5%). Emerging resistance against Nalidixic acid (39%) was observed. CONCLUSION Shigella still accounts for a significant proportion of bacillary dysentery in many tropical and subtropical countries. Serotype identification can help in devising strategies such as development of effective vaccine for controlling this problem. Increasing antibiotic resistance against commonly prescribed drugs signify that treatment options have become difficult in cases of severe dysentery.