Anti-PsaA and the risk of pneumococcal AOM and carriage.

Pneumococcal surface adhesin A (PsaA) is one of the common protein antigens of Streptococcus pneumoniae investigated as a possible vaccine candidate on the basis of studies in experimental animal models. The relation between the serum anti-PsaA concentration collected at 6, 12 and 18 months of age and the risk of pneumococcal carriage and acute otitis media (AOM) in the following 6 months was evaluated in 329 children of the Finnish Otitis Media (FinOM) Cohort Study. A higher anti-PsaA concentration at all three time points studied was found to predict a higher risk of pneumococcal carriage 6 months later. A higher anti-PsaA concentration at 6 months also predicted a higher risk of pneumococcal AOM during the following 6 months (RR 1.51, 95% CI 1.24-1.83), whereas a higher anti-PsaA concentration at 12 or 18 months seemed to decrease the risk of pneumococcal AOM (RR 0.94 [95% CI 0.80-1.09] and RR 0.88 [95% CI 0.73-1.07], respectively). These relations remained the same when concomitant risk factors for pneumococcal AOM were included in the models. Previous pneumococcal AOM was the most important risk factor for a subsequent pneumococcal AOM (RR 5.93 [95% CI 2.87-12.3], RR 2.2 [95% CI 1.21-4.00], and RR 3.3 [95% CI 1.72-6.32] during the three periods).