Objective: To examine the effects of a history of acute otitis media and different extrinsic factors on the risk of chronic otitis media with effusion in infancy.
Design: A retrospective birth cohort with a 2-year follow-up. Infection data were gathered from medical records and background information came from questionnaires. The monthly risk of chronic otitis media with effusion was dynamically modeled to control the confounding effects and time-dependency of the risk factors.
Setting: Primary health care centers, hospitals, and private practices in 10 randomly selected local government districts in the two northern most provinces of Finland.
Subjects: A random sample of 2512 children from the cohort.
Main outcome measures: Chronic otitis media with effusion, defined as a minimum of 2 months of middle-ear effusion, usually is disclosed by tympanocentesis and specific operative findings.
Results: Previous acute otitis media episodes were the greatest risk factor. Each acute episode induced a highly increased risk (odds ratio, 11.9; 95% confidence interval, 5.7 to 24.9) that disappeared in 3 months. Successive episodes were risky, but this risk also decreased rapidly. Other significant risk variables were attendance at a day nursery (odds ratio, 2.56; confidence interval, 1.17 to 5.57), male sex (odds ratio, 2.17; confidence interval, 1.37 to 3.44), and autumn season (odds ratio, 1.99; confidence interval, 1.11 to 3.55).
Conclusions: Acute otitis media episodes constitute the greatest risk of chronic otitis media with effusion. Each episode has a high transient risk for 3 months but no further direct effect on the risk.