What Causes an Ear Infection?

Ask the experts

What causes an ear infection?

Doctor's response

Bacteria and viruses can cause middle ear infections. Bacteria such as Streptococcus pneumoniae (pneumococcus), Hemophilus influenzae, Pseudomonas, and Moraxella account for about 85% of cases of acute otitis media. Viruses account for the remaining 15%. Affected infants under six weeks of age tend to have infections from a variety of different bacteria in the middle ear.

What are the risk factors for ear infection?

  • Bottlefeeding: The position of the breastfeeding child is better than that of the bottlefeeding position in terms of the function of the Eustachian tube that leads into the middle ear. If an infant needs to be bottlfed, it's better to hold the the baby rather than allowing them to lie down with the bottle. Ideally, they should not take the bottle to bed. (In addition to increasing the chance for acute infection, falling asleep with milk in the mouth enhances the risk of tooth decay.)
  • Upper respiratory tract infection: Children often develop upper respiratory infections prior to developing this type of infection. Exposure to groups of children (as in child care centers) results in more frequent colds, and therefore more earaches.
  • Exposure to air with irritants, such as tobacco smoke
  • Birth defects: Children with cleft palate or Down syndrome are more prone to ear infections.
  • Eustachian tube problems: Any problems with the Eustachian tubes (for example, blockage, malformation, inflammation) will increase the risk of infection. If the individual has allergies he or she may have swelling and blockage of one or both Eustachian tubes.
  • Immunosuppressed: Individuals with suppressed immunosuppression are at increased risk for ear infections.
  • Ear infections later in childhood: Children who have episodes of acute infections before six months of age tend to have more later in childhood.

Read our full medical article for more information on ear infection causes, symptoms, and treatments.

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Last Editorial Review: 10/3/2017
References
"Acute otitis media in adults"
UpToDate.com
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