Epidemiology

Group B streptococci (GBS) carriage rate varies by age and ethnicity.[5][6]

Approximately 10% to 30% of pregnant women are colonised with GBS in the rectum or vagina; in the absence of intervention, around 1% to 2% of babies born to colonised mothers will develop early-onset GBS infection.[6]

Rates of invasive neonatal infection vary considerably worldwide and have fallen in the US in recent years. From 1999 to 2005 in the US, rates were in the order of 0.35 per 1000 live births for early-onset disease (0-6 days after delivery), and 0.33 per 1000 live births for late-onset disease (7-89 days after delivery).[7] However, a 2018 US-based annual surveillance report estimated a fall in early-onset cases to 0.25 per 1000 live births, and late-onset cases to 0.28 per 1000 live births. The incidence was lowest in those aged 2 to 4 years and 5 to 17 years at 0.1 case per 100,000 population.[8]

One retrospective study of hospital-recorded neonatal GBS in England found no significant change in incidence between 1998 and 2017, with an average annual incidence of 1.28 per 1000 live births (95% CI 1.26 to 1.30).[9] However, analysis of UK surveillance data shows a different picture with an increase in early-onset neonatal GBS disease from 0.28 cases (in 2008) to 0.57 cases (in 2015) per 1000 live births, and in late-onset disease from 0.11 cases (in 1991) to 0.37 cases (in 2015) per 1000 live births.[10][11] The increased infection rates of late-onset disease may relate to increasing numbers of at-risk premature infants, and are broadly similar to rates reported in Finland, the Netherlands, and Norway. Varying rates of early-onset disease may reflect the different prevention strategies; the incidence of early-onset GBS disease in the US has declined by 80% since the 1990s when intrapartum antibiotic prophylaxis against GBS began.[6][12] The figures may also be confounded in part by improved national reporting rates and mandatory surveillance.

There is an ongoing disparity between rates of infection in black and white infants for both early- and late-onset disease. US surveillance reports in 2018 estimate a rate of 0.32 versus 0.24 cases per 1000 live births for early-onset disease in black and white infants respectively, and 0.52 versus 0.22 cases per 1000 live births in late-onset disease in black and white infants, respectively.[8]

Rates of invasive infection in non-pregnant adults vary considerably between countries; however, an increasing incidence of adult GBS disease has been observed worldwide. One meta-analysis encompassing data from 1975 to 2018 reported a pooled estimated incidence of 2.86 cases per 100,000 population across North America, South America, Europe, Asia, Australia, and Africa.[13] Colonisation rates in adults are similar regardless of age, but GBS disease becomes more prevalent and more severe in people aged >65 years.[13][14]

In the US, infection in non-pregnant adults accounts for the majority of cases of invasive GBS disease, with an observed increase in incidence from 8.1 to 10.9 cases per 100,000 adults from 2008 to 2016.[5] The incidence was higher in men and increased with age.[5] Incidence in black people was significantly higher than white people overall, although the absolute rate difference declined over time and was not significant in the data from 2016.[5]

Use of this content is subject to our disclaimer