Clonal structure and 21-year evolution of Streptococcus pneumoniae serotype 1 isolates in northern Spain.

This study of 135 serotype 1 pneumococcal isolates (88 invasive and 47 non-invasive), collected between 1987 and 2007, gave eight sequence types (217, 227, 228, 304, 305, 306, 3860 and 3861) that group, using eBurst, into three different lineages and one singleton. The annual incidence of serotype 1 invasive episodes per million inhabitants increased from 1.8 in 1987-1993 to 4.0 in 1994-2000, and to 25.6 in 2001-2007. ST228 was the predominant clone until 1998. ST306 first appeared in 1998 and became the most prevalent sequence type (>80%) after the introduction, in June 2001, of the heptavalent pneumococcal conjugate vaccine.