Serotypes and sequence types of pneumococci causing invasive disease in Scotland prior to the introduction of pneumococcal conjugate polysaccharide vaccines

Pneumococcal conjugate polysaccharide (Pnc) vaccines are now available, and the need for an improved understanding of circulating pneumococcal serotypes and sequence types (STs) is recognized. Three hundred sixty-eight pneumococci isolated in cases of invasive disease in Scotland in the first 6 months of 2003 were analyzed. The isolates belonged to 30 serotypes, and there was a strong correlation between serotype and ST, although only nine serotypes consisted of a single ST. The following serotypes coexisted with the following numbers of STs: serotype 14, 10 STs, serotype 8, 8 STs; serotype 4, 6 STs; serotype 22F, 8 STs; serotype 9V, 7 STs; serotype 23F, 6 STs; serotype 6B, 6 STs; serotype 1, 3 STs; serotype 3, 3 STs; and serotype 7F, 3 STs. Our data also showed a strong association between ST and serotype, although 19 STs contained multiple serotypes. Of the 10 most common STs, 6 coexisted with a single serotype each. Vaccine coverage in all age groups was 94.9% for the 23-valent polysaccharide vaccine and 50.7, 55.4, and 64.1% for the 7-, 9-, and 11-valent Pnc vaccines, respectively. For those under the age of 2 years, 79% coverage would be provided by the 7-, 9-, and 11-valent Pnc vaccines.