ASOM is most common in children between the ages of 3 to 7 years. Such infants have a short, wide, more horizonally placed eustachian tube than adults, allowing contamination from the regurgitation of feed. Poor sanitation, over-crowding and malnutrition are all risk factors in children. Risk factors in all age groups include recurrent or chronic rhinosinusitis, chest disease and eustachian tube dysfunction. Causes of eustachian tube dysfunction include hypertrophy of the adenoids, cleft palate and submucous cleft palate.

ASOM is a bacterial disease caused by pus forming organisms. Pathogenic bacteria have been isolated from the nasopharynx in up to 97% of children with ASOM. The bacterial infection may be a primary infection, or secondary following a viral acute non-suppurative otitis media. Bacteria enter the middle ear cleft via the eustachian tube, a tympanic membrane perforation or are blood-borne. Common organisms include: Beta haemolytic streptococcus (40%), Haemophilus influenzae (30%), Moraxella catarrhalis (10%).