To the Editor.—
The first strains of ampicillin-resistant Haemophilus influenzae in Dallas were recognized in 1975. Since that time all clinical isolates of H influenzae in the microbiology laboratories of Children's Medical Center and Parkland Memorial Hospital have been tested for β-lactamase production by the tube method of Catlin1 or by the paper strip method of Jorgensen et al.2Complete and accurate data are available only for strains from pediatric patients with meningitis and arthritis (Table). There has been a steady progression of increased frequency of β-lactamase-producing strains of from 3% to 6% per year to a current level of 22%. All strains were type B. Not included in the Table is a type D, biotype 2 strain, which was β-lactamase positive; it was isolated from a leukemic patient whose condition was bacteremic but who did not have meningitis or arthritis.Included are two strains from a patient in 1978 whose initial CSF isolate was β-lactamase negative. After 24 hours of ampicillin and chloramphenicol therapy, the CSF was sterile, and chloramphenicol therapy
Nelson JD. The Increasing Frequency of β-Lactamase-Producing Haemophilus influenzae B. JAMA. 1980;244(3):239. doi:10.1001/jama.1980.03310030015011
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