Population structure of group B streptococcus from a low-incidence region for invasive neonatal disease

The population structure of group B streptococcus (GBS) from a low-incidence region for invasive neonatal disease (Israel) was investigated using multilocus genotype data. The strain collection consisted of isolates from maternal carriage (n = 104) and invasive neonatal disease (n = 50), resolving into 46 sequence types. The most prevalent sequence types were ST-1 (17.5%), ST-19 (10.4%), ST-17 (9.7%), ST-22 (8.4%) and ST-23 (6.5%). Serotype III was the most common, accounting for 29.2% of the isolates. None of the serotypes was significantly associated with invasive neonatal disease. BURST analysis resolved the 46 sequence types into seven lineages (clonal complexes), from which only lineage ST-17, expressing serotype III only, was significantly associated with invasive neonatal disease. Lineage ST-22 expressed mainly serotype II, and was significantly associated with carriage. The distribution of the various sequence types and lineages, and the association of lineage ST-17 with invasive disease, are consistent with the results of analyses from a global GBS isolate collection. These findings could imply that the global variation in disease incidence is independent of the circulating GBS populations, and may be more affected by other risk factors for invasive GBS disease, or by different prevention strategies.