The efficacy of sulfadiazine in the treatment of Shigella infections, where the organism is sensitive to sulfonamides, has been well established,1-3 and because of its relatively low toxicity and general availability it has appeared to be the drug of choice in shigellosis therapy.3 However, the problem of the development of sulfonamideresistant strains was recognized in these early reports and independently reported by others.4 In recent years several investigators have reported outbreaks in which resistant strains have either predominated or have been the only strains isolated.5-7 Hardy's report,3 however, is the only one which has come to our attention which demonstrated the development of resistant strains during an outbreak, with the subsequent spread of sulfonamide-resistant infections in the study population.
An unusual opportunity to study the development of sulfadiazine resistance was afforded us by an outbreak of shigellosis due to Shigella sonnei Form I in an