National differences in incidence of acute mastoiditis: relationship to prescribing patterns of antibiotics for acute otitis media?

Background: Operating on the principle that most acute otitis media (AOM) episodes resolve without antibiotics, doctors in the Netherlands usually manage AOM in children with initial observation. Prescription of antibiotics is limited to children with a complicated course of AOM and those categorized as high risk. Consequently only 31% of patients with AOM receives antibiotics, compared with >90% in most other countries.

Objective: To substantiate the suggestion that this restrictive use of antibiotics leads to a higher incidence of acute mastoiditis.

Methods: A comparative study across several European countries, Canada, Australia and the United States was performed in the period 1991 to 1998. The incidence rate of acute mastoiditis was defined as the total number of patients age 14 years and younger discharged from all hospitals with the primary diagnosis of acute mastoiditis, during a specified period (usually 5 years), divided by the number of person years (py) in that same age range and period. The latter was calculated by totaling the midyear population estimate of children age 14 years and younger of each year. The 95% confidence intervals and incidence rate ratios were calculated to compare the observed rates.

Results: The incidence rate of acute mastoiditis in the Netherlands, with a low antibiotic prescription rate for AOM, was 3.8/100,000 py; in Norway and Denmark, with high prescription rates, the incidence rate was comparable at 3.5/100,000 py and 4.2/100,000 py, respectively. In all other countries with very high prescription rates, incidence rates were considerably lower, ranging from 1.2 to 2.0/100,000 py. The incidence rate in the Netherlands was about twice that in the United States (rate ratio, 0.5).

Conclusion: The incidence rate of acute mastoiditis in the Netherlands is higher than in many countries with higher antibiotic prescription rates. Although the potential benefits of restricted use of antibiotics (i.e. cost reduction, fewer side effects from antibiotics and less antimicrobial resistance) are beyond dispute, such strategy may be associated with a somewhat higher incidence of acute mastoiditis.