Prevalence of Bactericidal Antibodies to Haemophilus injluenzae, Type b

Sera from 1,205 persons, with a broad age span, were tested for bactericidal activity against Haemophilus infiuenzae, type b. The lowest prevalences of such antibodies were found among children aged one through four years and among adults over the age of 80 years. No positive correlation was observed between prevalence of antibodies and race, gravidity, or socioeconomic status. The highest prevalence was found among the parents of children who had had H. influenzae epiglottitis previously. Haemophilus infiuenzae, type b ' is the most fre-quent cause of bacterial meningitis in children under the age of four years in the United States [1]. Several centers have reported increases in the absolute and the proportional frequency of menin-gitis caused by this organism [2], as well as in-creases in severe infections in adults [3]. Because of these observations, questions have been raised concerning the current level of immunity to this organism in the population at large [4]. In 1933 Fothergill and Wright described an inverse relationship between the occurrence of H. influenzae meningitis and the presence of bac-tericidal activity for this organism in blood [5]. They pointed out that the highest incidence of Received for publication January 18, 1974, and in revised form April 22, 1974