OBJECTIVES:Group B streptococcus (GBS) disease remains a leading cause of morbidity and mortality in infants. There are limited data from China. The objectives of our study included defining the epidemiology of invasive GBS disease in Chinese infants <3 months of age at sentinel sites; and undertaking molecular characterization of the invasive disease strains by serotyping and multi-locus sequence typing (MLST).

METHODS：We conducted a passive, prospective laboratory-based, nationwide multi-center study in 18 sentinel hospitals from May 2016 to December 2017. We included infants aged < 3 months in whom GBS was cultured in a normally sterile site. We also retrospectively identified laboratory-confirmed invasive GBS cases documented between January 2015 and April 2016. Serotyping of GBS isolates was done by PCR; and sequencing of the seven housekeeping genes was evaluated by MLST.

RESULTS：A total of 304 cases were identified from January 2015 to December 2017, including 199 cases in 634,531 live-births. The overall incidence was 0.31 per 1000 live-births (95% CI 0.27-0.36), with substantial variability ranging from 0 to 0.76 per 1000 live-births across the 18 hospitals. The overall incidence of early-onset disease (<7 days age) and late-onset disease (7-89 days age) were 0.18 (95% CI 0.15-0.22) and 0.13 (95% CI 0.11-0.16), respectively. The case fatality ratio was 2.3%. The estimated annual number of GBS cases and deaths in China’s birth cohort would be 55,366 and 1273, respectively. The most frequent GBS serotype and clonal complex was serotype III (61.5%) and clonal complex 17 (40.6%), respectively.

CONCLUSIONS:This is the largest study on invasive GBS disease in infants from China. Our passive surveillance could underestimate the incidence. Enhanced active surveillance and the implementation of potential preventative strategies such as maternal vaccination, is urgently warranted.