Experimental otitis media with effusion induced by nonviable Hemophilus influenzae: cytologic and histologic study

In an earlier study the authors demonstrated that formalin-killed Hemophilus influenzae induces serous-type middle ear effusion in chinchillas and provides an excellent model for the study of human otitis media with effusion. The present study was initiated to evaluate the morphologic and histologic changes that occur in the middle ear after injection of this organism. All of the experimental animals injected with formalin-killed H. influenzae in the present study had straw-colored serous-type effusions within four days after injection. The submucosal thickness, mononuclear cell density, and capillary permeability all increased dramatically in the experimental animals. Marked bleeding, tissue edema, and cellular infiltration in the submucosa were prominent findings after injection of the inactivated bacteria. Half of the experimental animals had histologic evidence of marked proliferation of epithelial cells resembling adhesive otitis media. These findings suggest that nonviable H. influenzae are capable of inducing severe inflammatory changes in the middle ear and may play an important role in the pathogenesis of otitis media with effusion and its sequelae.