Frequency of isolation of various subtypes and antimicrobial resistance of Shigella from urban slums of Karachi, Pakistan

SummaryObjectivesShigellosis remains a major public health problem in developing countries. Antimicrobial resistance has complicated the empirical treatment. Knowledge of serotypes is crucial in vaccine development, as cross-protection between various serotypes is limited. Therefore we conducted a prospective study to determine the frequency of isolation of Shigella serotypes and antimicrobial resistance.MethodsStool samples from 8155 individuals, collected through a surveillance study conducted in four slums of Karachi from January 2002 to March 2004, were cultured. Results: Shigella was isolated in 394 (4.8%) of 8155 patients presenting with diarrhea. Two hundred and forty-two (62%) isolates were Shigellaflexneri, 72 (18%) were Shigellasonnei, 43 (11%) were Shigellaboydii, and 37 (9%) were Shigelladysenteriae. Thirteen S.flexneri serotypes were identified, of which the most frequent were 2a (38), 6 (37), and 1b (25), followed by 2b (23). Only 22 (5.6%) Shigella isolates were found to be pan-susceptible. Large proportions of isolates were resistant to co-trimoxazole (89% S.flexneri, 81% S.dysenteriae, 80% S.sonnei, and 56% S.boydii) and ampicillin (87% S.flexneri, 68% Sdysenteriae, 35% S.boydii, and 4% S.sonnei).ConclusionsConcurrent circulation of multiple strains with high resistance is worrying and mandates surveillance at the national level to facilitate the control of shigellosis.