OM is broadly defined as inflammation of the inner ear due to proliferation of bacteria and virus.
It is a continuum of a disease in that it is a consequence of an infection to the upper respiratory tract causing changes to the nasopharyngeal mucosa and subsequent Eustachian Tube dysfunction.

Viral Causes of OM
- Respiratory Syncytial Virus (RSV)
- Rhinovirus
- Adenovirus
- Coronavirus
- Bocavirus
- Influenza Virus
- Parainfluenza Virus
- Enterovirus
- Human Metapneumovirus
Bacterial causes of OM
- Streptococcus pneumoniae
- Nontypeable Haemophilus influenza
- Moraxella (Branhamella) catarrhalis
- Streptococcus pyogenes
- Mycoplasma spp.
- Mycobacterium tuberculosis
- Chlamydia trachomatis
The use of conjugate pneumococcal vaccine has decreased the number of episodes of OM associated with S. pneumoniae but a profound increased in incidence from H. influenza and M. cattarrhalis has been seen.