Haemophilus influenzae disease in the White Mountain Apaches: molecular epidemiology of a high risk population

Based on a 10-year retrospective and a 15-month prospective analysis, White Mountain Apache Indian children younger than 5 years were found to have an annual incidence of Haemophilus influenzae meningitis of 254 cases/100,000--an 8-fold higher incidence than that seen in the general United States population. In our prospective surveillance, H. influenzae isolates from cases of systemic disease were further characterized by capsular type, biotype and by outer membrane protein (OMP) and lipopolysaccharide (LPS) patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Unexpectedly, H. influenzae type a strains were isolated in 3/18 cases of systemic disease. All other disease-producing strains were type b. H. influenzae b strains possessing common OMP, LPS, capsular and biotype characteristics were isolated from individuals in geographically distinct communities within the reservation. These apparently identical strains were isolated from different individuals who had systemic infections that occurred months apart (longest interval, 14 months). Both OMP and LPS subtyping were necessary to discriminate among invasive H. influenzae isolates.