Antibody response to capsular polysaccharides of groups A and C neisseria meningitidis and Haemophilus influenzae type b during bacteremic disease.

Levels of antibodies to the capsular polysaccharides of groups A and C Neisseria meningitidis and Haemophilus influenzae type b were determined by radioimmunoassay in acute- and convalescent-phase sera of 377 patients with meningitis, septicemia, or epiglottitis. Diagnostic criteria, based on a fourfold or greater rise in antibody level and/or a high specific antibody level, correctly identified 85% of group A meningococcal diseases, 90% of group C meningococcal diseases, and 78% of H. influenzae type b diseases in children older than but only 15% in infants younger than 1.5 years of age. When levels of antibody in acute-phase sera were high, they were predominantly of the IgA class. A greater than fourfold rise in levels of antibodies to group A meningococcus was seen in 10%-32% of persons with disease caused by other bacteria, but minimal false-positive reactions occurred with group C meningococcus or H. influenzae type b.