Use of antiserum agar for detection of haemophilus influenzae type b in the pharynx

Abstract

An antiserum agar medium was-evaluated to determine its usefulness and accuracy in the study of the prevalence of Haemophilus influenzae type b (HIB) in the pharynx of infants and young children. The effects of varying the concentration of ingredients (Levinthal base, antiserum, and bacitracin) were demonstrated. The medium could be stored at 4° for periods up to 12 weeks with no loss of effectiveness. All halo-producing organisms detected after 24-40 hr of incubation were found to be HIB. When fewer than 20 colonies of HIB were.found on antiserum agar, HIB could not be detected on either rabbit blood agar or chocolate human blood agar simultaneously inoculated with throat swab fluids. Radial streaking with a 0.001-ml calibrated loop yielded at least twice as many isolated colonies with halos than did inoculation by streaking from a swabbed area of the plate. Oropharyngeal culture of 543 healthy Pittsburgh preschool children indicated that the prevalence of HIB is about 3% in children age 6 months through 3 years; HIB colonization was not observed during the first 6 months of life. There was a much higher carrier rate (65%) for siblings of patients with HIB meningitis or epiglottitis, as well as a greater intensity of colonization; nearly three-quarters of the sibling carriers had over 5 x 104 HIB colonies/throat swab. The medium is dependent on large amounts of potent and highly specific antiserum, a concentrated Levinthal base, and a refined agar. Its advantages are rapidity, sensitivity, specificity, and a potential for quantitation. The medium should be useful for carrier rate studies and for investigations of the role of HIB in such conditions as pneumonia, sinusitis, conjunctivitis, and orbital cellulitis of childhood. © 1975 International Pediatric Research Foundation, Inc.