Use of the 13-valent conjugate vaccine has the potential to eliminate pilus carrying isolates as causes of invasive pneumococcal disease

Abstract

We examined the distribution of the two pilus island loci (PI-1 and PI-2) in all pediatric invasive pneumococcal disease (IPD) isolates recovered in Portugal over the ten year period 1999–2008 (n=575). While 199 isolates (35%) harbored PI-2, only 98 isolates (17%) harbored PI-1. A decline of isolates carrying PI-1 was observed in the post 7-valent conjugate vaccine (PCV7) period since most PI-1 carrying isolates expressed PCV7 serotypes. On the other hand, the PI-2 increase in the post-PCV7 period was associated mostly with serotypes 1 and 7F. The overall proportion of piliated isolates declined in the period following PCV7 but quickly recovered to pre-PCV7 levels (50%). Only serotypes 19F and 19A contained isolates carrying simultaneously PI-1 and PI-2 and the proportion of isolates carrying both pilus islands remained stable and low. All PI-1 clades were represented in our collection and were associated with multiple serotypes. Over 99% of pilus island carrying isolates belonged to the 13-valent conjugate vaccine serotypes.