Otitis Media

Acute Otitis Media

Acute otitis media (AOM) remains one of the most frequently diagnosed infectious diseases in early childhood. By 3 years of age, 60% of children will have experienced at least one episode of AOM, and 24% will have experienced at least 3 episodes. Although the incidence of AOM has been declining, more than 5 million cases are annually diagnosed in the US. AOM diagnoses still constitute approximately 5% of all ambulatory visits. AOM remains an important cause of antibiotic prescriptions, healthcare visits, and use of medical resources.

Pathogenesis

The antecedent event in most (∼95%) cases of AOM is a symptomatic viral upper respiratory tract infection causing inflammation of the mucosa of the upper respiratory tract including the nasopharynx and eustachian tube. Asymptomatic colonization with respiratory viruses does not increase the risk of AOM. Viruses can be isolated from the nasopharynx in close to 80% of children with AOM. Eustachian tube dysfunction from inflammation impairs middle-ear fluid drainage and leads to aspiration and entrapment of nasopharyngeal bacterial pathogens. Approximately one-third of viral upper respiratory tract illnesses are complicated by AOM. Median time between the onset of URI and development of AOM is approximately 4 days. Bacteria are isolated from middle-ear fluid of approximately 80% of children with a bulging tympanic membrane (TM).

Viral infections alone (in the absence of a bacterial superinfection) infrequently (∼6% of cases) result in clinical features consistent with AOM. Of responsible viruses, RSV is the most frequently identified; approximately 10% of children with AOM have RSV in their middle-ear fluid. Fewer than 5% of children have other viruses detected alone.

Microbiology

Three bacterial pathogens predominate as causes of AOM: Streptococcus pneumoniae , non-typable Haemophilus influenzae , and Moraxella catarrhalis . In some series from outside the US, group A Streptococcus is present in ∼3% of cases. S. aureus is rarely isolated from the middle ear of children with intact tympanic membranes. This is in contrast to children with spontaneous rupture of the TM, in which the high rates of S. aureus could be related to contamination by the flora in the canal. ^,

Significant shifts in the balance of three predominant pathogens occurred since the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in 2000 and the 13-valent vaccine (PCV13) in 2010. In the year immediately following the introduction of PCV7 and PV13, dramatic decreases were observed in the prevalence of S . pneumoniae and relative increases in H. influenzae isolation from middle-ear aspirates. However, in the ensuing years, the prevalence of S. pneumoniae increased and H. influenzae proportions decreased, at least in several series. ^, At present, S. pneumoniae causes approximately 35%–40% of AOM cases, H. influenzae about 35%–40%, and M. catarrhalis about 25%.

Epidemiology

Age, sex, race, genetic factors, feeding practices, and environmental conditions likely affect the epidemiology of AOM. The peak incidence of AOM is in the first 2 years of life, particularly between ages 6 and 12 months. The increased susceptibility of infants may be explained, at least in part, by anatomic features (characteristics of the eustachian tube, such as short length, horizontal position, and high compliance) and immunologic factors (limited response to antigens and lack of previous exposure to common bacterial and viral pathogens). Younger age at the first episode of AOM increases the risk for recurrent episodes; one-third of children with AOM before 6 months will have an additional 4 episodes of AOM by the age of 2 years. Children who have Down syndrome or immunologic deficiencies (congenital or acquired) have a high incidence of AOM, as do children living near the Arctic Circle. Findings from twin and adoption studies suggest a strong genetic predisposition to otitis media; children with a strong family history of AOM are at higher risk of developing AOM. AOM also is a remarkably seasonal disease, occurring predominantly during the winter but also in the fall and spring. AOM almost always is seen in the setting of viral upper respiratory tract infection. Low socioeconomic status and exposure to large numbers of other children also are important risk factors for the development of AOM. Seasonality, age, and childcare exposures all probably relate to the risk of acquisition of viral upper respiratory tract infections. Receipt of PCV in infancy is strongly associated with a decrease in AOM, particularly AOM due to S. pneumoniae, AOM among children <2 years of age, and AOM requiring hospitalization. Overall, among children <2 years of age, who constitute the majority of those at risk for AOM, rates on AOM have decreased by approximately 50% since universal PCV immunization.

A study of the occurrence of AOM during the first 2 years of life in a sociodemographically diverse population of 2253 infants affirmed the importance of certain risk factors for the development and persistence of otitis media, particularly low socioeconomic status and exposure to a large number of children. Other less important variables independently related to the occurrence of otitis media were sex (boys more affected); duration of breastfeeding (longer more protective); and exposure to tobacco smoke. Of infants followed in this cohort, the proportions having ≥1episodes of middle-ear effusion (MEE) between age 2 months and ages 6, 12, and 24 months, respectively, were 48%, 79%, and 91%. Overall, the mean cumulative proportion of days during which MEE was present was 20.4% in the first year of life and 16.6% in the second year of life.