Common Pathogens

OM can be thought of as a disease continuum that usually begins with:

Viruses including: respiratory syncytial virus, rhinovirus, coronavirus, parainfluenza, influenza, adenovirus, and enterovirus, are often responsible for the first insult. These viruses can initiate the immune response causing tissue damage and migration of leukocytes to the area.

Virus, toxins and the immune response can damage the ciliated mucous membrane of the eustachian tube. When the cilia are lost or deranged, they are unable to move bacteria and secretions away from the middle ear. Local tissue swelling, inflammation and histologic changes further exaccerbate the problem, causing an obstructive dysfunction of the eustachian tube. The damaged membrane allows bacteria to adhere and colonize the tube and ME.

Prior to 2000 and the routine vaccination of children with the conjugated pneumococcal vaccine (PCV7) there were three main bacteria isolated by tympanocentesis from the middle ears of AOM patients. Streptococcus pneumoniae was responsible for more than 50% of pediatric AOM. Haemophilus influenzae was responsible for about 40% of AOM. Moraxella catarrhalis was responsible for less than 10%.

Less than a decade after routine childhood innoculation with PCV7, many studies are finding that the proportion of AOM cases due to Streptococcus pneumoniae have decreased. However, the incidence of AOM due to strains of S.pneumoniae not included in the vaccine has increased. Many of these strains are multi-drug resistant.

Surprisingly, Haemophilus influenzae is now responsible for about 60% of the pediatric AOM cases. Pathogenic organisms continue to display adaptive capacity to fill vacant niches and thwart treatment modalities.

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