A 16-year-old boy presents to the emergency department with severe right ear pain, itching, and discharge for the past 3 days. He reports sleeping on his left side since the onset of symptoms. He denies fevers or changes in his hearing. He is a three-sport athlete and is presently in swimming season. He denies any trauma to the ear. His temperature is 37.5°C (99.5°F), pulse is 86 beats/minute, and blood pressure is 100/70 mm Hg. Physical examination is significant for tenderness with tragal pressure and an edematous and erythematous external auditory canal.
Which of the following is the most likely etiology of the patient's symptoms?
The correct answer is:
C) Pseudomonas aeruginosa
This patient presenting with pain and irritation of the external auditory canal and history of recent water activity likely has otitis externa (OE) which is most frequently caused by Pseudomonas aeruginosa (38% of cases). OE can be differentiated from acute otitis media because of involvement of the external auditory canal and worsening pain with tugging on the ear. The tympanic membrane may be erythematous in OE though the presence of an air-fluid level along the tympanic membrane indicates a middle ear effusion and likely otitis media.
Answer choice A: Bacteroides spp., is incorrect. Anaerobic pathogens are present in 4-25% of cases of OE, and bacteroides and peptostreptococci are the most frequently involved anaerobes.
Answer choice B: Candida albicans, is incorrect. Fungal infection account for 2-10% of cases of OE and typically occur after treatment of a bacterial OE. Candidal infection classically occurs more often in patients who wear hearing aids.
Answer choice D: Staphylococcus aureus, is incorrect. Staphylococcus aureus represents approximately 8% of cases of OE.
Answer choice E: Staphylococcus epidermidis, is incorrect. Staphylocci as well as other aerobic and anaerobic bacteria normally colonize the external auditory canal. Staphylococcus epidermidis is one of the most common species which is a normal colonizer of the external canal.
Key Learning Point
Pseudomonas aeruginosa is the most common cause of otitis externa which typically presents with ear pain, itching, discharge, and hearing loss if the canal is edematous and narrowed. Physical findings include pain with tragal pressure as well as edema and erythema of the external auditory canal.
