Group B streptococcus neonatal invasive infections in Belgium 2010-2017, and characterization of isolated strains.

Introduction/Background & Aims:
Where intrapartum antibiotic-prophylaxis (IAP) is given to pregnant women colonized with Group B Streptococcus (GBS), the incidence of neonatal early-onset disease (EOD) has been successfully reduced; nevertheless, GBS is still the leading cause of severe disease among newborns, notably because the incidence of GBS late-onset disease (LOD) is not affected by IAP. Another strategy such as maternal immunization for prevention of both EOD/LOD is highly desirable worldwide.
Aiming to describe GBS epidemiology and characterization of relevant epidemiological markers for vaccine development, surveillance of isolates causing neonatal disease is needed.
We provide here results from the Belgian surveillance organized by the National Reference Centre(NRC).
Methods:
A total of 292 strains of GBS isolated from blood culture/cerebro-spinal fluid of newborns with invasive disease (149 EOD; 143 LOD) were sent to NRC by laboratories of a surveillance network, through years 2010-2017. Capsular-polysaccharide (CPS)-typing and pili-typing were performed with multiplex PCR assays. Multilocus sequence-typing and assignment to the hypervirulent clonal-complex (CC)17 was determined.
Results:
CPS type III isolates were responsible for 38.9% (n=58) of EOD cases, followed mainly by types Ia, V and II (22.1%, 18.1%, 8.1%). LOD cases were mainly caused by type III isolates (n=107, 74.8%), followed by types Ia (12.6%), V, Ib, IV and II (4.2%, 3.5%,2.8%, 2.1%). These distributions did not vary during the study period. A pili type was assigned to all isolates: at least one pili gene, PI2a, PI2b, or a combination of genes PI1-PI2a and PI1-PI2b. In 2016-2017, the hypervirulent-clone CC17 accounted for 33.3% of EOD (70.4% of type III) and 67% of LOD (89% of type III).
Conclusions:
The Belgian CPS distributions of isolates from EOD/LOD were similar to European data.
One or 2 of 3 pilus-genes were detected in all isolates.
CPS type III was predominant in both EOD/LOD and was mainly represented by CC-17 strains.