Acute otitis media (AOM) develops when eustachian tube dysfunction (shorter, more horizontal, and more compliant in children) leads to negative middle ear pressure and fluid accumulation (effusion). Bacterial colonization of this effusion by Streptococcus pneumoniae, non-typeable Haemophilus influenzae, or Moraxella catarrhalis triggers an acute inflammatory response. The 2013 AAP guidelines require a bulging tympanic membrane (TM) for definitive AOM diagnosis, distinguishing true AOM from otitis media with effusion (OME), which does not require antibiotics. Moderate-to-severe bulging has a 98% positive predictive value for bacterial AOM, while TM erythema alone has poor diagnostic specificity (often caused by crying or fever).