Outer membrane protein subtypes and investigation of recurrent Haemophilus influenzae type b disease

Ten previously healthy patients, ages 3 to 26 months, developed recurrent episodes of deep-tissue Haemophilus influenzae type b infections from 4 to 191 days (median = 28 days) after the last day of antibiotic therapy given for the first episode. None of the patients had a persistent focus of infection and eight were considered to have had adequate therapy for the initial episode. Bacteremia, without evidence of relapse at the site of the original infection, was documented in eight of the ten recurrent episodes. The ampicillin susceptibilities of the HITB isolates changed between episodes in two of the patients. Blood or CSF isolates from both episodes in seven patients were examined for biotypes and outer membrane protein subtypes. Concordance of both biotype and OMP subtype was present for all seven paired isolates, including the two pairs in which the HITB ampicillin sensitivities had changed. These data imply that some patients become reinfected with their original HITB isolates and that OMP and capsular antigens do not always elicit protective immunity, even after natural infection.