Pathogenesis

Few details are known about the pathogenesis of acute bacterial conjunctivitis. Probably, the organisms are inoculated directly onto the conjunctiva from airborne respiratory droplets or rubbed in from contaminated hands. Like most bacterial pathogens, they resist destruction by lysozyme. Otitis media is sometimes developing at the time conjunctivitis is diagnosed. Generally, otitis media and sinusitis are preceded by infection of the nasal chamber and nasopharynx. Probably, infection spreads upward through the eustachian tube to the middle ear (figure 23.7). The infection damages the ciliated cells, resulting in inflammation and swelling. Since the damaged eustachian tube cannot move secretions from the middle ear, pressure builds up from fluid and pus collecting behind the eardrum. The throbbing ache of a middle ear infection is produced by pressure on nerves supplying the middle ear. Bacterial infections of the middle ear can cause the eardrum to perforate, giving discharge of blood or pus from the ear and immediate relief from pain. With treatment, the eardrum perforations usually heal promptly. The pressure in the middle ear can force infected material into the mastoid air cells, resulting in mastoiditis. The fluid behind the eardrum impairs movement of the drum, thereby decreas-

Mastoiditis Anatomy

Figure 23.7 Otitis Media A stylized view of the infected middle ear showing accumulation of fluid, swelling of the eustachian tube, and outward bulging of the eardrum.The inset shows a ventilation tube placed in the eardrum to equalize middle ear pressure in individuals with chronically malfunctioning eustachian tubes.

Figure 23.7 Otitis Media A stylized view of the infected middle ear showing accumulation of fluid, swelling of the eustachian tube, and outward bulging of the eardrum.The inset shows a ventilation tube placed in the eardrum to equalize middle ear pressure in individuals with chronically malfunctioning eustachian tubes.

ing ability to hear. Because of the fluid, some young children cannot hear clearly and show a delay in normal speech development. Spread of infection from the nasopharynx to the sinuses probably occurs by a mechanism similar to that in otitis media. Both middle ear and sinus infections sometimes spread to the coverings of the brain, causing meningitis.

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