Molecular analysis of Streptococcus pneumoniae clones causing invasive disease in children in Singapore

Streptococcus pneumoniae remains a leading cause of serious paediatric disease. However, there are few published epidemiological data regarding invasive pneumococcal disease (IPD) in many countries in South East Asia, including Singapore. Baseline data for IPD are essential to inform policy regarding pneumococcal conjugate vaccine (PCV) use in Singapore. To our knowledge, this is the first study to use multilocus sequence typing (MLST) to investigate clonal relationships among Singaporean IPD isolates. We characterized 86 invasive pneumococci isolated from Singaporean children between 2001 and 2006 using serotyping and MLST. The objectives were to compare Singaporean MLST data to worldwide data and to assess serotype distribution in relation to current PCV formulations. We observed 50 sequence types (STs), a high proportion of which (n = 16) were novel STs. Despite the presence of these novel STs, serotype distribution was similar to that observed elsewhere. Serotypes 14, 6B, 19A and 19F accounted for 85 % of IPD cases. PCV7, PCV10 and PCV13 covered 85 %, 86 % and 97 % of IPD isolates, respectively. We have demonstrated a pressing need for larger studies to determine the molecular epidemiology and antibiotic susceptibility of circulating pneumococcal clones from both carriage and disease in Singapore.