Read condition-specific symptoms and clinical context for Streptococcus agalactiae. A common gut and genital-tract resident in adults that occasionally causes serious infection in newborns.
CDC states that group B Streptococcus bacteria commonly live in people’s gastrointestinal and genital tracts, and that pregnant women can pass the bacteria to their babies during delivery, with most babies who get GBS disease in the first week of life exposed this way. PHAC describes a Gram-positive facultative anaerobe measuring 0.5-1.0 by 1.0-2.0 micrometres, appearing in pairs or chains of up to 50 cells or more, beta-haemolytic on blood agar, with nine serotypes. PHAC reports that 10 to 30% of women are colonized and asymptomatic, and that about 2% of all infants are infected although 75% of infants exposed are colonized without any clinical signs. Carriage is therefore the usual outcome and disease the exception.
PHAC describes early-onset infection occurring within the first 24 to 48 hours and up to 7 days of life, with an incubation period of less than 7 days. CDC states that most babies who get GBS disease in the first week of life are exposed during delivery.
Possible symptoms: Respiratory distress; Fever; Lethargy; Irritability; Pauses in breathing (apnea); Low blood pressure.
PHAC states that neonatal infections with S. agalactiae have a 20% mortality rate. This describes diagnosed neonatal infections, not the risk to a baby born to a colonized mother — PHAC also records that 75% of exposed infants are colonized without any clinical signs. Clinical decisions belong with the care team.
PHAC describes late-onset disease at 1 to 3 months of age, which is more likely to cause bacteremia or meningitis, the latter in 25% of cases.
Possible symptoms: Bloodstream infection; Meningitis; Fever; Poor feeding and lethargy.
Late-onset disease occurs after the delivery-related window, so it is not prevented by measures taken at birth alone. Assessment of an unwell infant is urgent and clinical.
CDC states that bloodstream infections, pneumonia, and skin and bone infections are the most common GBS infections among men and non-pregnant women. PHAC adds peripartum chorioamnionitis and bacteremia in new mothers.
Possible symptoms: Bloodstream infection; Pneumonia; Skin and bone infections.
PHAC states that GBS is only fatal in adults who are immunocompromised or elderly, giving a mortality rate of 15% in patients aged 65 or older. That is a figure for diagnosed invasive infection in that age group, not a population risk.
CDC states that these bacteria commonly live in people’s gastrointestinal and genital tracts.
PHAC reports that 10 to 30% of women are colonized and are asymptomatic, and that 75% of infants exposed are colonized without any clinical signs. There is no symptom list for colonisation and none is invented here. Colonisation is the usual state, not an early stage of disease: PHAC records that about 2% of all infants are infected, so most exposure does not lead to illness. A positive carriage swab describes where the bacterium is living, not a diagnosis.
Screening in pregnancy and any decisions that follow are clinical guidance handled by maternity services, and are not reproduced here.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.