Background
Acute otitis media (AOM) is a common childhood infection characterised by middle ear effusion, inflammation of the tympanic cavity and the rapid onset of symptoms and signs of an acute inflammation [
1]. Approximately 75% of non-PCV immunized children are estimated to have at least one AOM episode before the age of 5 [
2]. By the age of two years, up to 5% of children have experienced recurrent AOM, defined as three or more AOM episodes in six months or four or more episodes in one year [
3]. AOM is a leading cause of office visits and antibiotic prescriptions in children [
4‐
7]. Healthcare resource utilization associated with the management of AOM and AOM-related surgical procedures is substantial [
8‐
10]. Although rare, complications of AOM such as acute mastoiditis and meningitis are associated with significant morbidity [
11‐
13].
Streptococcus pneumoniae (S. pneumoniae) is a common bacterial cause of AOM [
14,
15]. The incidence of AOM has declined in Europe and globally since the introduction of pneumococcal conjugate vaccines (PCVs) [
16‐
20]. In Germany, universal vaccination of children aged < 2 years with the 7-valent PCV (PCV7) was recommended in 2006 and was replaced by 10- and 13-valent PCVs in 2009 (PCV10 and PCV13) [
21]. In Germany vaccinations are voluntary, although strongly advised by health authorities. Statutory health insurance (SHIs) providers pay for vaccinations recommended by the German standing committee on vaccination (STIKO) and in alignment with the official vaccination guidelines published by the Robert Koch Institute [
22]. Vaccinations are therefore free of charge via individuals’ SHI package. Public opinions on vaccination are generally positive [
23]. The schedule for PCV vaccination in children is at two, four and 11–14 months old.
To better understand the potential value of new vaccines in Germany, it is important to quantify the current incidence of AOM. However, post-PCV13 data on AOM is lacking. In the present study, we therefore aimed to provide recent estimates for the incidence of all-cause AOM (overall, simple, and recurrent), AOM-related surgical procedures and AOM-related complications over time in children < 16 years old in Germany.
Discussion
Next generation, higher-valent pneumococcal vaccines are under development to further reduce the burden of pneumococcal disease, including AOM [
33‐
35]. To better understand the potential value of new vaccines in Germany, the present study provides recent estimates of the incidence of AOM in the post-PCV-13 era. AOM overall, simple AOM and recurrent AOM declined significantly over the study period (2014–2019). AOM incidence (overall, simple and recurrent) was greatest in children 2–4 years, followed by incidence in children < 2 years, and 5–15 years. Although the overall incidence of AOM declined over the study period, the incidence of complications increased and the incidence of AOM-related surgical procedures remained constant. AOM-related surgical procedures were again highest in children aged 2–4 years. IRs of AOM-related complications were similar across age groups.
Variations in study design, timeframe, case definition and age-groups complicate comparisons of IRs between AOM studies. Nonetheless, our results are consistent with the only other study of AOM incidence in Germany. In a prospective cohort study conducted after the introduction of PCV7 (2008–2010) in Germany, the incidence of physician-diagnosed AOM was 311 and 218/ 1,000 CY in children 0–2 and 3–5 years respectively [
2]. Our study, after the introduction of PCV13, found a further decline in AOM incidence in children aged < 2 years, from 209/ 1,000 CY in 2014 to 147/ 1,000 CY in 2019. This is unsurprising, as in 2010, PCV13-PCV7 serotypes accounted for 60% of pneumococcal isolates in children < 5 years with spontaneous otorrhea [
36].
Several studies before and after the introduction of PCV7 have demonstrated the significant impact of PCV introduction on pneumococcal serotype distribution in Germany. Two bacterial etiology studies were conducted in children < 5 years with spontaneously draining AOM prior to (1995–2007) and following the introduction of PCV7 (2008–2011) [
36,
37]. Serotypes included in PCV7 accounted for 60.3% of pneumococcal isolates in the pre-vaccination period compared to only 8.3% of isolates following PCV7 introduction. A third study showed that diagnosis rates for suppurative and non-suppurative otitis media declined by 19% and 26%, respectively, in the post-vaccination period (2007–2011) compared to the pre-vaccination period (2003–2011) [
3]. Furthermore, a more recent follow-up study demonstrated a dramatic decrease (-86%) in cases of AOM caused by
S. pneumoniae over the seven study years (2008–2014); with a total disappearance of PCV7 and PCV13 serotypes, except for serotype 3 [
38].
Other studies have observed significant declines in AOM IRs in children following PCV introduction. A recent study in Israel demonstrated a downward trend of IRs of AOM during the post-PCV years in children aged < 9 years (August 2009–2018;
P < 0.001) [
39]. The largest decrease (21%) was observed in children aged < 1 year, from 807/ 1,000 children during the pre-PCV years to 640/ 1,000 during the post-PCV years (
P < 0.001). Similar results have been observed in children aged ≤ 5 years in Sweden: with a 2.3% decrease in otitis media and AOM following PCV13 introduction [
40].
In this study, we found AOM incidence to be highest in the 2–4-year-old age group. Our findings are supported by studies in Italy and Eastern Europe. A study among children aged 0–6 years utilising the Italian Pedianet database (2003–2007) found that AOM incidence was highest in the 3–4 year old age group (222/ 1,000 CY; CI 218–227) [
17]. Similarly, among children aged < 6 years in five Eastern European countries, AOM incidence was highest in the 3–4 year age group (209/ 1,000 CY; CI 165–261) between June 2011 and January 2013 [
41]. Potential explanations in Italy may be the age at which children begin school and family size. Differences in the age distribution in Italy compared with other countries (where incidence is highest among children aged 6–24 months [
42‐
44]) is likely due to day-care attendance, which in Italy typically starts around 3 years of age. Similarly, in Germany, kindergarten is typically attended by children between 3 and 6 years old [
45]. It is well established that children who attend day-care have higher AOM IRs than their non-attending counterparts [
45]. The small size of the average Italian family (2.47 members) and German family (2.0 members) may also reduce the risk of infections for infants through exposure to other children.
This study provides the most recent estimates of AOM-related surgical procedures in Germany. The incidence of AOM-related surgical procedures (myringotomy, tympanostomy tube removal, exploratory tympanotomy, tympanotomy with sealing of the round and/ or oval window membrane) remained steady throughout the study period, despite a decrease in the overall rate of AOM. A similar study in the US (2001–2011) observed a downward trend in the incidence of myringotomy/ ventilation tube insertion immediately after PCV13 introduction [
26]. Similar trends have been observed in Sweden, with a downward trend in tympanostomy tube placement and myringotomy procedures after PCV13, compared with pre-PCV cohorts [
46]. However, our findings (2014–2019) may be explained by the increase in AOM-related complications. Other studies have also found an increasing burden of AOM-related complications in the post-PCV era [
26,
47‐
51]. Shifts in AOM etiology or pneumococcal serotype distribution as a result of PCV introduction can impact the incidence of AOM (overall, simple, or recurrent) and AOM-related surgical procedures and complications to different degrees. We were unable to further evaluate these trends in the current study due to lack of pathogen or serotype information in the InGef database.
The main strength of this study is the precision of the estimates due to the large study population and representativeness of the InGef database (approximately 4 million insured members). Previous studies have demonstrated age, sex, morbidity, mortality and drug prescription/dispensation distributions to be similar in the InGef database and German population [
25]; although representativeness in terms of other factors such as socioeconomic status have not been assessed.
There were several limitations to this study. First, exact diagnosis dates were not available in the outpatient data so quarterly diagnosis dates were used instead. Antibiotic prescriptions and diagnostic tests during the quarters with AOM diagnoses were assumed to be related to AOM to assign exact diagnosis dates. However, this may have still led to inaccurate identification of AOM diagnosis dates. Second, misclassification bias due to coding inaccuracies of AOM is possible. However, this potential bias would serve to underestimate the incidence of AOM and our findings are not out of line with other studies [
2,
17,
36,
37]. Furthermore, ICD-9 or ICD-10 codes have been used to identify AOM in many prior studies assessing AOM incidence, including recent studies in Germany and the US [
52,
53].
In addition, the use of antibiotics prescriptions or diagnostic tests to validate an AOM diagnosis, may have led to a further underestimation of the true incidence of AOM in Germany as not all AOM episodes may have been treated with antibiotics or involved a diagnostic test. In many countries, including Germany, AOM clinical guidelines call for watchful waiting and to refrain from prescribing antibiotics for all AOM episodes [
54]. However, the most recent AOM clinical guidelines in Germany explicitly state that those patients with uncomplicated AOM can initially be treated purely symptomatically, only if they undergo clinical examination and otomicroscopy/otoscopy (one of the diagnostic tests in the present study) after 2 to 3 days [
28]. Therefore, uncomplicated AOM cases not treated with antibiotics should still have been captured through the presence of an otoscopy code. Updated standardised guidelines for the diagnosis and treatment of AOM in Germany are currently in development by the Arbeitsgemeinschaft der wissenschaltlichen medizinischen Fachgesellschaften (AWMF), due for completion at the end of 2023 [
55].
Similarly, the focus in the present study was on extracranial AOM-related complications, and intracranial complications such as meningitis were therefore not captured [
56]. The AOM-related complication rate is therefore likely to be underestimated. However, of the 221,123 patients who had AOM, only 96 had meningitis anytime across the study period. Therefore, seeing as meningitis is a rare complication, the number of patients developing meningitis within 21 days of an AOM episode is likely to be negligible [
26]. Furthermore, not all AOM-related surgical procedures, for example mastoidectomy or drainage of the subperiosteal mastoid abscess, may have been captured due to the limitation of the procedure codes available in the InGef database. However, while mastoidectomy was a common surgical intervention associated with AOM in the pre-antimicrobial era, it is now believed to be performed in fewer than 5 cases per 100,000 people with AOM [
57]. Indeed, other similar published studies have not included mastoidectomy when looking at surgical procedures associated with AOM or reported such low rates that statistical analysis was fruitless [
19,
31].
A further limitation is that the IRs estimated in this study were not adjusted for covariates such as sex or chronic diseases as the aim of this study was to describe the incidence of AOM and AOM-related complications/surgical procedures in different age groups. Results are therefore presented as crude rates and CIs.
Finally, information on viral or bacterial AOM, causative pathogen (e.g., Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis) and serotype distribution was not available. An understanding of prevalent and emerging pneumococcal serotypes will be critical when considering the development and introduction of novel vaccines to reduce residual disease burden.
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