A 14-year-old presenting with a red and bulging left tympanic membrane for 3 days indicates what possibility?

A red and bulging left tympanic membrane in a 14-year-old suggests the presence of otitis media, particularly because of the acute nature of the symptoms lasting for three days. Bacterial otitis media is characterized by the presence of purulent effusion in the middle ear, which often results in visible changes like redness, swelling, and bulging of the tympanic membrane.

In this case, the acute onset and appearance of the tympanic membrane are indicative of inflammation typically caused by a bacterial infection. The rapid progression of symptoms and physical examination findings align well with common presentations of bacterial otitis media, especially in children and adolescents.

While viral otitis media can also cause similar symptoms, it usually does not present with the same degree of bulging and significant redness and is often less severe. Allergic rhinitis and chronic sinusitis are less likely to cause such definitive findings on the tympanic membrane and generally do not cause the same acute bulging appearance.

Therefore, the clinical presentation strongly aligns with bacterial otitis media, making it the most likely diagnosis.