Table 2 Inclusion and exclusion criteria

Children aged 9–36 months

Children with orofacial cleft

Children with at least one Greenlandic born parent and at least one Greenlandic born grandparent

Children with Down’s syndrome

American Society of Anaesthesiologists’ physical status classification class 1 and 2

Children with known generalized immune deficiency

B-type curve, defined as flat line tympanograms or gradient <0.04 ml, or C2-type curve, defined as pressure ≤ −200 dPa, measured by tympanometry at two visits three-four months apart or

Children formerly treated with ventilation tubes

three episodes of acute otitis media in 6 months according to medical charts or

Lack of signed informed consent, signed by the legal guardian

tour episodes of acute otitis media in 12 months according to medical charts

Signed informed consent, signed by the legal guardian