To the Editor.
—In the October issue of the Journal we reported a study of shigellosis in outpatients conducted in 1969 and 1970 demonstrating the bacteriological and clinical effectiveness of ampicillin.1 This work confirmed previously reported observations of effectiveness made in hospitalized children with severe shigellosis.2 Since the outpatient manuscript was submitted for publication (in March, 1972) increasing numbers of ampicillin-resistant shigellae have been isolated in our area. In addition the incidence of infection due to Shigella sonnei appears to be rising in our patients.Forty-three percent of 197 strains of shigellae isolated in 1971 from children on one of our pediatric services (Children's Medical Center) were S sonnei. From Jan 1 through October of 1972, 53% of 105 Shigella strains were S sonnei. In 1971 only 1% of S sonnei strains were resistant to ampicillin in vitro but this has risen to 25% in the first ten