The Emergence of Haemophilus influenzae Types e and f as Significant Pathogens

Non-type b encapsulated Haemophilus influenzae meningitis (two cases due to H. influenzae type e, two due to H. influenzae type f) was diagnosed in four children in a 6-month period at the University of Virginia. H. influenzae type b was the most common cause of bacterial meningitis in the United States before the introduction of an effective vaccine, whereas the other five encapsulated serotypes of H. influenzae rarely caused invasive disease. The clinical features of non-type b H. influenzae meningitis and the therapy for this infection are the same as those for type b H. influenzae disease. We report these four cases to document an increase in infection due to non-type b serotypes of H. influenzae, and we postulate that this change may result from the well-documented decrease in H. influenzae type b oropharyngeal carriage and disease that has occurred because of universal vaccination for H. influenzae type b.