Clinical research question: Can OM-85 reduce the recurrence of respiratory tract infections (RTIs) in children with AH by stimulating the immunological response of the host and therefore, as a consequence reduce the size of adenoid tissue in children with adenoid hypertrophy? Can this prevent further complications such as surgery need? Half of participants will receive OM-85, while other half will receive a placebo.

OM-85 significantly reduces RTIs in children. This effect was proved by many clinical studies and meta-analyses. A Cochrane meta-analysis first published in 2006 and updated recently (Del-Rio-Navarro 2012) showed that immunostimulants (IS) could reduce acute RTIs (ARTIs) by almost 39% when compared to placebo. Among the different IS, OM-85 showed the most robust evidence with 4 trials of "A quality" according to the Cochrane grading criteria. Pooling six OM-85 studies, the Cochrane review reported a mean number of ARTIs reduction by -1.20 [95% Confidence Interval (CI): -1.75, -0.66 ] and a percentage difference in ARTIs by -35.9% [95% CI: -49.46, -22.35 ] compared to placebo.

Adenoid hypertrophy (AH) is one of the most important respiratory disease in preschool children. In normal conditions adenoid tissue enlarges up to 5 years and become smaller afterwards. But in some children who have recurrent upper respiratory tract infections (URTI)s, it keeps growing and this can be associated with complications. AH may cause recurrent respiratory infections and each infection contribute to enlargement of adenoid tissue thus promoting a vicious cycle. Additionally enlarged adenoids are known to be reservoir for microbes and cause of recurrent or long lasting RTIs.

AH is associated with chronic cough, recurrent and chronic sinusitis, recurrent tonsillitis, recurrent otitis media with effusion, recurrent other respiratory problems such as, nasal obstruction and sleep disturbances, sleep apneas. Eventually, AH causes loss of appetite and growth delay; it is often associated with misusing or over use of antibiotics and often eventually requires surgery. It decreases quality of life both in children and parents and it represents a burden not only for families but also for health care system and society due to increased health cost4.

In one study which investigated the structural and immunological aspects of tonsils and adenoids of 105 children (54 males and 51 females, aged between 4 and 18 years) who were affected by chronic inflammatory hypertrophy of palatine tonsils and adenoids which had not responded to previous medical treatments and who underwent adenotonsillectomy because of recurrent inflammatory episodes with fever, it was demonstrated that deficit in the activa-tion of the immune system could be represented by the small quan-tity of messenger ribonucleic acid (mRNA)s for interleukin-2 (IL-2) and interleukin-4 (IL-4) detected in our population, suggesting a defective activation of Th1 and Th2 lymphocytes.

Inclusion Criteria:

• Children (age: 2-6 years)
• Who experienced recurrent RTIs (at least 3 episodes in 6 months before the inclusion)
• Who have symptoms of AH (snoring; mouth breathing awake; mouth breathing asleep; nasal congestion; hyponasal voice; chronic nasal discharge; daytime drowsiness, or hyperactivity; restless sleep; sleep apnoea <15 sec; night cough; and poor oral intake/weight loss) based on the symptoms score questionnaire

Exclusion Criteria:

• Atopy
• Gastroesophageal reflux
• Immune deficiency
• Asthma or allergic rhinitis
• Premature delivery
• Anatomic alterations of the respiratory tract; chronic respiratory diseases (tuberculosis and cystic fibrosis); autoimmune disease; liver
• Kidney failure; malnutrition; cancer
• Treatment with inhaled or systemic corticosteroids within the previous month
• Treatment with immunosuppressants, immunostimulants, gamma globulins, or anticonvulsive drugs within the previous 6 months.

Randomization will be done by throwing the coin. Family of patients and doctor (Coordinator / Responsible Investigator Serap Ozmen and Associate Investigator Soner Sahin) will be blind; Researcher Ilknur Bostanci and assistant researcher Gulay Senel will appoint drugs and placebo.