Emergence of antimicrobial-resistant shigellosis in Oregon

Ampicillin and trimethoprim-sulfamethoxazole (TMP-SMZ) are currently considered acceptable empirical therapy for shigellosis in developed countries. However, there are few recently reported studies on antimicrobial resistance among shigellae isolated in the United States. We examined the epidemiology of shigellosis and the antimicrobial susceptibility of Shigella species isolated in Oregon from July 1995 through June 1998. Of 430 isolates, 410 were identified to the species level: Shigella sonnei accounted for 55% of isolates, and Shigella flexneri, for 40%. The overall annual incidence of shigellosis was 4.4 cases per 100,000 population. Children aged <5 years (annual incidence, 19.6 cases per 100,000 population) and Hispanics (annual incidence, 28.4 cases per 100,000 population) were at highest risk. Of 369 isolates tested, 59% were resistant to TMP-SMZ, 63% were resistant to ampicillin, 1% were resistant to cefixime, and 0.3% were resistant to nalidixic acid; none of the isolates were resistant to ciprofloxacin. Thirteen percent of the isolates had multidrug resistance to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline. Infections due to multidrug-resistant shigellae are endemic in Oregon. Neither ampicillin nor TMP-SMZ should be considered appropriate empirical therapy for shigellosis any longer; when antibiotics are indicated, a quinolone or cefixime should be used.