The most severe form of group B streptococcal disease is neonatal meningitis in infants, which is frequently lethal and can cause permanent neuro-cognitive impairment.

[6] Hemolytic GBS strains, when cultivated on granada medium after 24-48h at 35-37 °C, produce (granadaene) and develop as orange-brick or red colonies that allow its straightforward and unequivocal identification.

[19] GBS urinary tract infections, more than 100.000 CFU (colony forming units) /mL, may induce labour in pregnant women and cause premature delivery (preterm birth) and miscarriage and requires antibiotic treatment.

[29][30] Because of that, a previous sibling with GBS-EOD is also an important risk factor for the development of the infection in subsequent deliveries, probably reflecting the lack of protective antibodies in the mother.

[12][22] Overall, the case fatality rates from GBS-EOD have declined, from 50% observed in studies from the 1970s to between 2 and 10% in recent years, mainly as a consequence of improvements in therapy and management.

Intravenous penicillin or ampicillin given to GBS-colonized women at the onset of labor and then again every four hours until delivery have been proven to be very effective at preventing vertical transmission of GBS from mother to baby and GBS-EOD.

[12] IAP has been considered to be associated with the emergence of resistant bacterial strains and with an increase in the incidence of early-onset infections caused by other pathogens, mainly Gram-negative bacteria such as Escherichia coli.

[47] The culture-based screening approach identifies candidates using lower vaginal and rectal cultures obtained between 35 and 37 weeks of gestation (or 36–37),[14] and IAP is administered to all GBS colonized women.

The risk-based strategy identifies candidates to receive IAP by the aforementioned risk factors known to increase the probability of GBS-EOD without considering if the mother is or is not a GBS carrier.

[12][24][50] IAP is not required for women undergoing planned cesarean section in the absence of labour and with intact membranes, irrespective of the known GBS carriage status.

ACOG recommendations state,[14] "Women with a positive prenatal GBS culture result who undergo a cesarean birth before the onset of labor and with intact membranes do not require IAP".

[57] Up to 90% of cases of GBS-EOD would be preventable if IAP were offered to all GBS carriers identified by universal screening late in pregnancy, plus to the mothers in higher risk situations.

This involves growing the samples in a selective enriched broth medium to improve the viability of the GBS and simultaneously impairing the growth of other naturally occurring bacteria.

[6][7][12][14] In the UK, this is the method described by the Public Health England's UK Standards for Microbiology Investigations[69] After incubation the enrichment broth can also be subcultured to granada medium agar where GBS grows as pinkish-red colonies, and further identification tests are not required[6][9][70][71] After incubation the enrichment broth can also be subcultured to chromogenic agars, where GBS grows as coloured colonies.

[14] The US Preventive Services Task Force and ACOG recommend routine urine screening for all pregnant women early in their pregnancies, even in the absence of urinary symptoms, in order to detect asymptomatic bacteriuria.

As with UTIs, any asymptomatic bacteriuria (not just GBS) cases with high CFU/mL values have also been shown to induce pyelonephritis, low birth weight, and preterm deliveries.

[78] Therefore, treatment of these asymptomatic cases of bacteriuria with antibiotics at the time of diagnosis is just as important as treating symptomatic UTIs in pregnancy in order to reduce these risks.

Around 25% of women having home births probably carry GBS in their vaginas at delivery without knowing, and it could be difficult to follow correctly the recommendations of IAP and to deal with the risk of a severe allergic reaction to the antibiotics outside of a hospital setting.

[18] In 2008, after widespread use of antenatal screening and intrapartum antibiotic prophylaxis, the Centers for Disease Control and Prevention in the United States reported an incidence of 0.28 cases of GBS-EOD per thousand live births in the US.

[104] The following are estimates of the chances that a baby will be infected with a GBS neonatal infection if no preventive measures are taken and no other risk factors are present:[105] If a woman who carries GBS is given IAP during labor, the baby's risk is reduced significantly: The Royal College of Obstetricians and Gynaecologists (RCOG) first issued their Green Top Guideline No 36 "Prevention of early onset neonatal Group B streptococcal disease" in 2003.

This guideline clearly stated: "Routine bacteriological screening of all pregnant women for antenatal GBS carriage is not recommended, and vaginal swabs should not be taken during pregnancy unless there is a clinical indication to do so."

However, the guideline states that "At the first antenatal (booking) appointment (and later if appropriate), discuss and give information on .... infections that can impact on the baby in pregnancy or during birth (such as group B streptococcus, herpes simplex, and cytomegalovirus)"[108] Nevertheless, the NICE Neonatal Infection guideline states: "Offer antibiotics during labor to women who: The UK National Screening Committee's current policy position on GBS is: "screening should not be offered to all pregnant women.

[110] This decision was strongly criticized by the charity Group B Strep Support as ignoring both the wishes of the public and the rising incidence rates of GBS infection in the UK.

CDC also recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors.

ASM also states that it is acceptable to use NAAT-based identification of GBS from an enrichment broth (after 18-24-hour incubation) with high sensitivity, and that FDA-cleared commercial assays are available to perform the test.

[114] ACOG also allows for the use of NAATs without the enrichment broth,[14] despite the high false negative rate, as a rapid POCT (point-of-care) test for women who present in labor with unknown GBS status.

[8][14] National guidelines in most countries advocate the use of universal screening of pregnant women late in pregnancy to detect GBS carriage and use of IAP in all colonized mothers.

e.g. Canada,[115] Spain,[116] Switzerland,[117] Germany,[118] Poland,[119] Czech Republic,[120] France,[121] Belgium,[122] Argentina[123] and Colombia[124] In contrast, risk factor-based guidelines were issued (in addition to the UK [87]) in the Netherlands,[125] The Royal Australian and New Zealand College of Obstetricians and Gynaecologists recommends that all maternity units should have an established plan for the prevention of neonatal GBS disease.

Serious life-threatening invasive GBS infections are increasingly recognized in the elderly and in individuals compromised by underlying diseases such as diabetes, cirrhosis and cancer.

[163] It has also been reported a human foodborne outbreak of invasive disease caused by the consumption of GBS-infected tilapia [163] Vaccines to protect fish against GBS infections are under development.