The Pathogenesis of Disease Due to Type b Haemophilus influenzae

Haemophilus influenzae is a Gram-negative bacterium that was first described by Pfeiffer in 1892 (1 ). This ubiquitous, human-specific organism was originally thought to be the etiologic agent of “influenza.” However, H. influenzae was not consistently isolated from autopsied lungs of individuals who had died during the influenza pandemic in 1918. The confusion that existed about the relationship between the prevalence of H. influenzae and human disease was relieved when Pittman discovered that strains of this bacterium could be divided into two groups, encapsulated (typeable) and nonencapsulated (nontypeable) strains (2 ). Pittman further distinguished six encapsulated types of H. influenzae , designated a–f, by the serological specificities of their capsular polysaccharide (2 ).