The first precondition for the development of acute otitis media is exposure to an organism capable of causing the infection. Otitis media can be caused by either viruses or bacteria. Virus infections account for about 15% of cases. The three most common bacterial pathogens are Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis. As of 2003, about 75% of ear infections caused by S. pneumoniae are reported to be resistant to penicillin.
Otitis media may also be caused by other disease organisms, including Bordetella pertussis, the causative agent of whooping cough, and Pneumocystis carinii, which often causes opportunistic infections in patients with AIDS.
There are other factors that make the development of an ear infection more likely. Because the eustachian tube has a more horizontal orientation and is considerably shorter in early childhood, material from the nasopharynx can easily reach the middle ear. Discharges from the nasopharynx include infection-causing organisms. Children also have a lot of lymph tissue, some of which makes up the adenoids, in the area of the eustachian tube. The adenoids may enlarge with repeated respiratory tract infections, ultimately blocking the eustachian tubes. When the eustachian tube is blocked, the middle ear is more likely to fill with fluid. This fluid increases the risk of infection, and the corresponding risks of hearing loss and delayed speech development.
Recent advances in gene mapping have led to the discovery of genetic factors that increase a child's susceptibility to otitis media. Researchers are hoping to develop molecular diagnostic assays that will help to identify children at risk for severe ear infections.
Most cases of acute otitis media occur during the course of a URI. Symptoms may include cold symptoms, fever, ear pain, irritability, and problems with hearing. Babies may have difficulty feeding. When significant fluid is present within the middle ear, pain can increase depending on position. Lying down may cause an increase in painful pressure within the middle ear, so that babies often fuss if not held upright. Older children sometimes complain of a full sensation in the affected ear. If the fluid build-up behind the eardrum is sufficient, the eardrum may develop a hole (perforate), causing bloody fluid or greenish-yellow pus to drip from the ear. Although the pain may be severe before the eardrum perforates, the pain is usually relieved by the reduction of pressure brought on by a perforation.
Judith Turner, Rebecca J. Frey PhD, The Gale Group Inc., Gale, Detroit,