he reduction of childhood mortality is one of the millennium development goals (MDG 4) of the World Health Organization (WHO). Although substantial improvements have been made, more than 40% of deaths in children under 5 years of age worldwide occur during the neonatal period [1]. Streptococcus agalactiae, also referred to as Lancefield Group B Streptococcus (GBS), has been identified as a major contributor to neonatal morbidity and mortality since the 1970s [2-5]. Recent investigations from the African continent confirmed GBS as an important pathogen causing neonatal sepsis [6, 7].

Newborns usually acquire the encapsulated gram-positive cocci vertically from their mothers before or during delivery. Worldwide, between 10–37% of healthy pregnant women are colonised recto-vaginally by GBS [8-10]. Of these, 50% transfer the bacteria to their neonates, of whom approximately 1% develops invasive disease [11].

Early onset disease (EOD) occurs with sepsis within the first 6 days of life and tends to progress rapidly, particularly since some neonates are already septicaemic at birth [12]. Late onset disease (LOD) affects newborns between the 7th and 90th day of life with a peak 1 month after birth and commonly presents with bacteraemia and meningitis.

An extensive meta-analysis by Edmond et al. [13] included 74 studies from countries all over the world and revealed a mean incidence of GBS-related invasive disease in infants 0–98 days of age of 0.53 per 1000 live births (95% confidence interval (CI): 0.44–0.62) and a mean case fatality rate of 9.6% (95% CI: 7.5–11.8). Dagnew et al. [1] found even higher incidences of up to 3.06 per 1000 live births in resource-poor settings in South Africa. Notably, variations between countries and continents were high overall. Yet, data from Africa are scarce because only 5% of the available studies were conducted on the continent [13].

Group B Streptococcus contains an antigenically diverse polysaccharide antigen (capsular polysaccharides (CPS)), by which it can be further divided into ten unique subtypes (Ia, Ib, II – X). As one of the major virulence factors, CPS enables bacterial evasion from phagocytic clearance [14]. Globally, the five serotypes Ia, Ib, II, III and V are most frequently associated with invasive disease and account for 85% of cases [13]. Serotype III alone caused 37% of EOD and 53% of LOD worldwide [13]. However, predominating serotypes vary geographically, as for instance serotypes Ia and III cause the majority of infections in the United States, while serotypes IV and VIII were the most common strains in pregnant women in Japan [15, 16].

The first risk- and screening-based prophylactic approaches against invasive GBS-related neonatal diseases were implemented in the early 1990s [17, 18] and have led to a significant decline of incidences of invasive disease [19-21]. Screening of pregnant women between 35 and 37 weeks gestation for GBS carriage and subsequent administration of intravenous intrapartum antibiotic prophylaxis (IAP) to positive women turned out to be the most effective intervention to protect newborns against GBS-EOD [22-24]. However, IAP appears to be less effective against LOD. Moreover, despite IAP being routinely performed, EOD may still occur as women may be colonised after being screened [20, 23, 25]. Above all, developing countries that have the highest incidences of neonatal invasive disease are widely lacking the infrastructure to implement routine screening programmes.

In the last two decades, extensive efforts have been undertaken to develop GBS vaccines for women of childbearing age [26, 27]. Effective immunisation against the most prevalent serotypes could protect neonates from GBS infection and subsequent GBS-related disease. To date, several polysaccharide and conjugated vaccine candidates have been assessed or are still assessed in clinical trials [28-30].

The aim of this study was to provide data on the prevalence and serotype distribution of GBS in women in late pregnancy living in rural and urban areas of Ghana, West Africa, to serve as a basis for future vaccine trials in the region.