Characterization of the genetic lineages responsible for pneumococcal invasive disease in Portugal.

The availability of a conjugate vaccine has the potential to reduce the disease burden of pneumococci and to alter the serotype frequency in the disease-causing population through immunoselection. These changes will probably be reflected in the distributions of individual genetic lineages within the population. We present a characterization of a collection of recent (1999 to 2002) invasive isolates from Portugal (n = 465) by macrorestriction profiling with pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. During this time, serotypes 14, 1, 3, 4, 8, 9V, 23F, 7F, 19A, and 12B were the 10 most prevalent overall by decreasing rank order. By combining the PFGE data with the sequence types (STs) of 104 isolates, we were able to identify the genetic lineages of the majority of the isolates. We found 66 STs, including 20 novel STs, corresponding to 47 different lineages by e-BURST analysis. We found in our collection a number of previously identified internationally disseminated lineages, especially among macrolide-resistant and penicillin-resistant isolates, and these accounted for most of the isolates. Most of the major lineages (17 of 25) were identified in all years of the study, suggesting that the pneumococcal population associated with invasive disease was stable. This study provides a characterization of the pneumococcal population associated with invasive disease that will be useful for detecting potential selective effects of the novel conjugate vaccine.