Group B Streptococcus In Babies

Introduction

The bacterial genus Streptococci comprises a broad group of Gram-positive bacteria that are highly significant to humans due to their close affinity to the human body as part of the normal microbiological flora, despite their potential to cause episodic severe diseases. Among the various serogroups, subgroup B stands out as particularly significant due to its capacity to cause sepsis and severe meningitis in newborn babies.¹

According to the World Health Organization (WHO), Streptococcus agalactiae (also called Group B Streptococcus or ‘GBS’) is one of the major causative agents for bacterial meningitis in babies worldwide. Additionally, the WHO reports that, on average, 18% of pregnant women carry this bacterium worldwide, potentially affecting up to 2 out of every 1000 live-born infants.²

Understanding Group B Streptococcus

According to the Lancefield classification, a method used to classify Streptococcus bacteria, there are 20 distinct subtypes of GBS. The subtypes are grouped based on the presence or absence of a special type of polysaccharide and teichoic acid, which exhibit antigenic properties in Streptococcus. This classification ranges from the English alphabet A to S, with Group B streptococcus being one of these subgroups.^1,3

Group B streptococcus was first identified by Nocard in 1887 in bovine animals. As it was the main representative bacterium causing a lack of milk production in bovine animals, it was named Streptococcus agalactiae. Later, the bacterium was discovered in pregnant women after extensive research.

In the 1970s, it was found that the same bacterium can cause severe sepsis in newborn babies and meningitis if left untreated. It was also found to be a leading cause of stillbirth. Currently, it is reported that GBS is commonly present in the reproductive and gastrointestinal tracts of pregnant women.^1,3

Microbiology of GBS

GBS is gram-positive bacteria that appears as pairs or chains of cocci. When grown on blood agar, GBS forms small colourless colonies that cause complete haemolysis (destruction of red blood cells), due to the production of a toxin that lyses (destroys by disintegration of the cell membrane) red blood cells. 

All strains of GBS share a common cell wall carbohydrate antigen, and they can be classified into different types based on their surface capsular polysaccharides. Additionally, a surface protein antigen called C protein is common to certain strains and helps in enhanced attachment to host cells. GBS also produces beta-hemolysin, a toxin that destroys red blood cells, and C5a-ase, an enzyme that inactivates the accumulation of neutrophils at the infection site and helps the bacteria evade the host immune system.³

Transmission of GBS

When pregnant women have GBS in their bodies, the bacteria can move up from the urinary or reproductive tract to the uterus or bladder. If they reach the uterus, they might affect the foetal membranes, causing a condition called chorioamnionitis. This can lead to problems like premature labour, miscarriage, or even the death of the unborn baby.³

Alternatively, during vaginal delivery, the bacteria can pass to the baby through the amniotic fluid. This can lead to inflammation in the baby's lungs, known as GBS pneumonia. In some cases, the bacteria can be more harmful, causing damage to the baby's lung tissue with a toxin called beta-hemolysin, which leads to bacteremia, a serious infection in the bloodstream, and sepsis in newborns. Sometimes, the bacteria can even cross into the baby's brain through the blood-brain barrier, leading to meningitis, an infection in the cerebral spinal fluid.³

Lastly, though less common, the bacteria can also spread through the bloodstream to the joints, causing a condition called septic arthritis.

Risk factors for GBS in babies

In most cases, GBS isn't harmful for pregnant women, and they often don't even know they have it until they're tested during pregnancy. Routine tests are usually done to check for GBS, especially in developed countries where healthcare is more accessible. Unfortunately, in underdeveloped countries, these tests are often not available, which increases the risk of babies becoming infected with GBS and potentially dying from this infection.^1,2,3,4

If GBS is found in pregnant women, they are usually given appropriate treatment to prevent any complications. It's also important for women who have had GBS in a previous pregnancy to inform their midwife or another specialist in charge of their care.

Babies born in hospitals are closely monitored by specialists, but once they leave the hospital, it's essential for the mother or whoever is taking care of the baby to watch for any signs of illness for the next three months. This helps to ensure that any symptoms of GBS infection are caught early and treated promptly.⁴

Common symptoms of GBS in newborns include:⁴

• High or low temperature and/or skin feels too hot or cold
• Abnormally fast or slow heart rate or breathing rate
• Difficulties in breathing or struggling to breathe
• Not cooperating while feeding
• Changes in skin colour

Some other symptoms which might be hard to distinguish from other conditions:⁵

• Continuously crying
• Not responding or significantly less activity

Diagnosis and testing

Prenatal screening for GBS

GBS can be detected during pregnancy through vaginal or rectal swabs or a urine test. Screening is not routinely offered to pregnant women in the UK, but if a woman has risk factors or a history of GBS infection in a previous pregnancy, her healthcare provider may recommend screening to determine if GBS is present.⁴

Diagnostic tests for GBS in babies

Diagnosing GBS infection in newborns involves definitive testing, typically through culturing the organism from a sterile body site. Meningitis in early-onset disease can be challenging to distinguish clinically from bacteremia as in some cases, blood cultures may come back negative even when meningitis is present. As a result of this lumbar puncture is often necessary to assess meningeal involvement.

While rapid antigen detection methods exist, they are not recommended as substitutes for cultures from blood or other sterile body fluid specimens. Additionally, repeating antigen tests during therapy is not advised. Emerging methods like real-time PCR show promise in detecting GBS DNA in the blood but require further evaluation through prospective studies to determine their sensitivity and specificity.^3,4

Treatment and management

Antibiotics for GBS in newborns

Newborns diagnosed with GBS infection are typically treated with antibiotics promptly. If there are signs of GBS or if the baby is suspected to have it, antibiotics are administered as soon as possible. The first line of antibiotics are Ampicillin and Gentamicin. These antibiotics are crucial and can be life-saving for babies with suspected infections. Treatment is continued for at least 36 hours, and if there are no signs of infection and all tests come back negative, the antibiotics are stopped.^3,4

Supportive care for babies with GBS

Babies with suspected or confirmed GBS infection receive supportive care, which includes close monitoring of their general well-being, heart rate, temperature, breathing, and feeding for at least 12 hours. This monitoring helps healthcare providers detect any signs of infection early on. Additionally, babies recovering from GBS meningitis undergo a diagnostic auditory brainstem response (ABR) test.^3,4

Preventive measures for pregnant women

To prevent GBS infection in newborns, pregnant women who test positive for GBS during labour are given antibiotics through a drip. Antibiotics are also administered to pregnant women diagnosed with GBS in their urine to treat urinary tract infections and prevent transmission to the baby during birth.^3,4

Importance of hygiene practices

Maintaining good hygiene practices is crucial. This means practising cleanliness in personal hygiene routines like hand washing regularly, particularly before handling newborns or preparing food. Hygiene also extends to keeping living spaces clean and ensuring that surfaces and objects are sanitised, reducing the risk of GBS transmission. By prioritising hygiene practices, individuals can help minimise the spread of GBS and protect both themselves and vulnerable populations, such as pregnant women and newborns, from potential infections.⁵

Current research and developments

Vaccine development efforts

The WHO recognised Group B Streptococcus as a significant pathogen affecting newborns and infants, prompting efforts to develop vaccines for prevention.² Several GBS vaccines are currently in development worldwide. Research indicates that antibodies against different GBS strains can be passed from mothers to their babies, offering protection after birth. This discovery suggests that a successful GBS vaccine could provide immunity to newborns through maternal immunisation.⁶

Ongoing studies, like PREPARE, aim to determine the antibody levels needed for protection against GBS strains prevalent in different regions. This data will help inform vaccine development strategies.^2,6

GBS vaccines have undergone testing in animals and early trials in adults, including non-pregnant women. Results have shown promising outcomes, such as delaying bacterial carriage without safety concerns. Further research is needed to evaluate these vaccines' effectiveness in pregnant women and their ability to pass antibodies to protect infants. Recent trials involving pregnant women have not raised any safety concerns, indicating the potential for safe and effective GBS vaccines in the future.⁶

Summary

In summary, Group B Streptococcus (GBS) is a big issue, especially for newborns, and can cause serious problems if not treated. However, new progress in knowing how it works, how it spreads, how to diagnose it, and how to treat it has led to better ways to deal with it.

Ongoing vaccine development work looks promising for reducing GBS infections in pregnant women and babies. By putting together these efforts with good prevention plans and making more people aware of GBS, we can move towards a future where GBS-related sickness and death reduce, making women and babies healthier around the world.