Objective The effect of adenoidectomy on nasopharyngeal colonisation of pathogens has not previously been evaluated. The authors studied the effect of adenoidectomy on nasopharyngeal colonisation by bacteria causing otitis media and the effect of adenoidectomy on the development of pneumococcal capsular polysaccharide antibodies.

Design Randomised controlled study.

Setting Tertiary care centre.

Patients 217 children aged 12–48 months who had recurrent or persistent otitis media were randomised. 166 children were followed up for 3 years.

Intervention Random allocation to undergo adenoidectomy or not to undergo adenoidectomy. All the children underwent insertion of tympanostomy tubes.

Main outcome measures Nasopharyngeal colonisation by pneumococci, Haemophilus influenzae and Moraxella catarrhalis 1, 2 and 3 years after randomisation. Serum IgG antibodies against pneumococcal capsular polysaccharide serotypes 6B, 14, 19F and 23F 3 years after randomisation.

Results After the first year of randomisation adenoidectomy increased nasopharyngeal carriage of pneumococci (RR, 1.47; 95% CI 1.04 to 2.07) but it did not influence the carriage of H influenzae or M catarrhalis. Among carriers of serotype 6B pneumococci, adenoidectomy resulted in lower concentrations of pneumococcal serotype 6B polysaccharide antibodies (ratio of geometric means of antibody concentrations, 0.37; 95% CI 0.16 to 0.85). Concentrations of serotype 14, 19F and 23F antibodies seemed not to be influenced by adenoidectomy. Despite this, adenoidectomy resulted in a significant increase in nasopharyngeal carriage of serotype 19F pneumococci.

Conclusions Adenoidectomy increases the risk of nasopharyngeal carriage of pneumococci in children younger than 4 years of age. This may be independent of the development of serum IgG capsular polysaccharide antibodies.