Invasive Haemophilus influenzae Type b (Hib) Infection in an Adult Patient with a Selective Deficiency of Antibody to the Hib Capsular Polysaccharide

A 31-year-old woman without any underlying disease contracted severe invasive Haemophilus influenzae type b (Hib) infection but developed no antibodies to the Hib capsular polysaccharide. Serum immunoglobulin levels were normal, but she had an isolated deficiency of antibody to Hib. Subsequently, immunization with a tetanus toxoid–conjugated Hib vaccine induced only a minimal response. However, she had a protective level of antibody (1 mg/mL) after the fifth vaccination. Invasive Haemophilus influenzae type b (Hib) infections oc- lymphocyte subsets; and response to mitogen activation. HIV serology was negative, but she had IgG antibodies to severalcur almost exclusively in young children and are rarely seen other viruses.in adults [1]. Protective antibodies to the Hib capsular polysac-The levels of all IgG antibodies to Hib CP were studied bycharide (CP) are normally acquired during childhood and there-using a previously described avidin-biotin–based ELISA [4]after prevent invasive Hib disease [2]. The low immunogenicity with some modifications. Briefly, microplates were precoatedof bacterial polysaccharides in young children can be overcome with 5 mg of avidin/mL, and after overnight incubation, theyby coupling the CP to protein carriers, a technique used in were coated with biotinylated Hib CP (concentration, 2current conjugated Hib vaccines [3]. Such conjugated Hib vac-mg/mL). After blocking of nonspecific binding, serum samplescines were in 1993 (the time of investigation of this case) in serial dilutions were incubated overnight. Mouse antibodyincluded in the Swedish infant vaccination program