Recent (1984 to 1992) trends in the antimicrobial resistance of Shigella isolates in Israel were studied by analyzing the results of 106,000 stool cultures, 3,511 of which yielded Shigella spp. Over the study period, resistance to trimethoprim-sulfamethoxazole (TMP-SMX) increased from 59 to 92% (P ‫؍‬ 0.0038) and that to ampicillin increased from 13 to 86% (P < 0.0001). Resistances to nalidixic acid, chloramphenicol, and broad-spectrum cephalosporins remained low. Shigella sonnei, which currently accounts for 90% of Shigella infections, was more resistant than S. flexneri to TMP-SMX (81 versus 57%, P < 10 ؊6 ), ampicillin (42 versus 32%, P < 10 ؊5 ), and tetracycline (38 versus 28%, P < 10 ؊5 ). S. boydii and S. dysenteriae were relatively rare. Seasonality in antimicrobial resistance was found, with summer isolates being less resistant to TMP-SMX, ampicillin, or both than isolates obtained over the rest of the year (P < 10 ؊5

Trends in the epidemiology of infections due to Shigella species over a period of 6 years (1986-1991) in Israel were studied by analysis of the results of 51,300 stool cultures, of which 2,987 yielded Shigella species. In a university hospital, the relative prevalence of Shigella sonnei in patients with shigellosis increased over the years from 60% in 1986 to 91% in 1991 (r = 0.93; P = .007); concomitantly, the prevalence of Shigella flexneri decreased from 29% to only 8% (r = -0.80; P < .05). In the community, the increase in prevalence of S. sonnei was more moderate and occurred only from 1989 to 1991. Since 1990, S. sonnei has been isolated from more hospitalized patients than has S. flexneri, in contrast to their rates of isolation in the past. The increase in prevalence of S. sonnei was most prominent among children, in whom it caused 94% of shigella infections in 1991. Shigella boydii and Shigella dysenteriae remained relatively rare, causing approximately 5% and approximately 1%, respectively, of the cases of shigella infection. Concomitantly, the antimicrobial resistance of S. sonnei has become significantly greater, and it is currently 2.7 and 1.6 times higher than that of S. flexneri to trimethoprim-sulfamethoxazole and ampicillin, respectively. We conclude that the relative frequency of S. sonnei is increasing, especially in hospitalized patients, and hypothesize that this may be related to its increasing antimicrobial resistance. These trends have clinical implications.