Otitis Externa (External Ear Infections)
Otitis externa is similar to skin and soft tissue infection. Two major types of external otitis exist: acute or chronic.
Acute external otitis may be localized or diffuse. Acute localized disease occurs in the form of a pustule or furuncle and typically is caused by Staphylococcus aureus. Erysipelas caused by group A streptococci may involve the external ear canal and the soft tissue of the ear. Acute diffuse otitis externa (swimmer’s ear) is related to maceration (softening of tissue) of the ear from swimming or hot, humid weather. Gram-negative bacilli, particularly Pseudomonas aeruginosa, play an important role. A severe, hemorrhagic external otitis caused by P. aeruginosa is difficult to treat and has occasionally been related to hot tub use.
Chronic otitis externa results from the irritation of drainage from the middle ear in patients with chronic, suppurative otitis media and a perforated eardrum. Malignant otitis externa is a necrotizing infection that spreads to adjacent areas of soft tissue, cartilage, and bone. If allowed to progress and spread into the central nervous system or vascular channel, a life-threatening condition may develop. P. aeruginosa, in particular, and anaerobes are frequently associated with this process. Malignant otitis media is seen in patients with diabetes who have blood vessel disease of the tissues overlying the temporal bone in which poor local perfusion of tissues results in an environment conducive for invasion by bacteria. On occasion, external otitis can extend into the cartilage of the ear, usually requiring surgical intervention. Certain viruses may infect the external auditory canal, the soft tissue of the ear, or the tympanic mem brane; influenza A virus is a suspected, but not an established, cause. VZV may cause painful vesicles within the soft tissue of the ear and the ear canal. Viral agents such as influenza are the bacterial agents typically associated with acute otitis media (S. pneumoniae, H. influenzae, and M. catarrhalis). Mycoplasma pneumoniae is rarely associated with this condition.
Otitis Media (Middle Ear Infections)
In children (in whom otitis media is most common), pneumococci (33% of cases) and Haemophilus influenzae (20%) are the usual etiologic agents in acute disease. Group A streptococci (Streptococcus pyogenes) are the third most frequently encountered agents, found in 8% of cases. Other organisms, encountered in 1% to 6% of cases, include Moraxella catarrhalis, Staphylococcus aureus, gram-negative enteric bacilli, and anaerobes; in one recent study, M. catarrhalis, S. pneumoniae, and H. influenzae were the most common bacterial pathogens. Viruses, chiefly respiratory syncytial virus (RSV) and influenza virus, have been recovered from the middle ear fluid of 4% of children with acute or chronic otitis media. Chlamydia trachomatis and Mycoplasma pneumoniae have occasionally been isolated from middle ear aspirates. Otitis media with effusion (fluid) is considered a chronic sequela of acute otitis media. A slowly growing organism, Alloiococcus otitis is a pathogen that has been isolated from patients with otitis media with effusion.
Chronic otitis media yields a predominantly anaerobic flora, with Peptostreptococcus spp., Bacteroides fragilis group, Prevotella melaninogenica (pigmented, anaerobic, gram negative rods), Porphyromonas, other Prevotella spp., and Fusobacterium nucleatum as the principal pathogens; less frequently present are S. aureus, Pseudomonas aeruginosa, Proteus spp., and other gram-negative facultative bacilli. Table 1 summarizes the major causes of ear infections.
Table1. Major Infectious Causes of Ear Disease
The mastoid is a portion of the temporal bone (lower sides of the skull) containing the mastoid sinuses (cavities). Mastoiditis is a complication of chronic otitis media in which organisms find their way into the mastoid sinuses. To prevent the further spread of this infection to the central nervous system, a mastoidectomy is performed.
