Streptococcus agalactiae is a type of bacteria commonly known as Group B Streptococcus, or GBS. This bacterium is a gram-positive coccus, meaning it is a round-shaped bacterium that stains purple in a Gram stain test and tends to form chains. GBS is frequently found living in the human body, often without causing any illness. Despite its presence, GBS can sometimes lead to serious infections, particularly in vulnerable populations.
Colonization Versus Infection
The presence of Streptococcus agalactiae in or on the body without causing any signs of illness is called colonization. GBS commonly colonizes the gastrointestinal and genitourinary tracts in many healthy adults. This means the bacteria are simply living there without invading tissues or triggering an immune response.
In contrast, an active GBS infection occurs when the bacteria invade the body’s tissues, multiply, and cause a host immune response, leading to disease symptoms. For most healthy individuals, being colonized with GBS is asymptomatic and does not require treatment.
Risk Factors for Infection
While GBS can colonize many people harmlessly, certain populations face a higher risk of developing an active infection. Newborns are particularly susceptible, as their immune systems are still developing and may not be able to mount an adequate defense against the bacteria. Transmission from mother to infant can occur during passage through the birth canal or, less commonly, through ascending infection within the womb.
Pregnant individuals also face increased risk, with GBS potentially causing urinary tract infections, intra-amniotic infections, or postpartum infections. Other groups with compromised immunity or underlying health conditions are also more vulnerable. This includes the elderly and people with chronic illnesses such as diabetes, heart disease, or liver disease.
Symptoms and Associated Illnesses
GBS infections manifest differently depending on the age group affected, with distinct symptoms and associated illnesses. In newborns, GBS can cause severe conditions classified as early-onset or late-onset disease. Early-onset disease typically appears within the first week of life, often within the first 24 hours.
Symptoms may include fever, difficulty feeding, lethargy, irritability, and breathing problems such as grunting sounds or rapid breathing. These symptoms can progress to serious conditions like sepsis, pneumonia, or meningitis. Late-onset disease occurs in infants between one week and three months of age, with similar symptoms including fever, poor feeding, and irritability. Meningitis is more commonly associated with late-onset GBS infections in infants.
In adults, GBS infections generally present with less severe symptoms compared to newborns. Common adult infections include urinary tract infections (UTIs), which may cause a burning sensation during urination or frequent urges. GBS can also lead to skin and soft-tissue infections, appearing as red, swollen, and painful areas of the skin.
More severe adult infections can involve bacteremia or pneumonia, causing symptoms like fever, chills, or shortness of breath. While less common, GBS can also cause meningitis or bone and joint infections in adults, particularly in those with underlying health issues. Pregnant individuals may experience fever, abdominal pain, or increased heart rate if they develop a uterine infection.
Screening and Diagnosis
For pregnant individuals, routine screening for GBS colonization is a standard part of prenatal care. This screening is typically performed between 36 and 37 weeks of pregnancy. The process involves a healthcare provider using a sterile swab to collect samples from both the lower vagina and the rectum.
These samples are then sent to a laboratory for culture to determine the presence of GBS bacteria. A positive screening result indicates colonization, not an active infection. This screening helps identify those who may transmit GBS to their newborn during delivery.
When an active GBS infection is suspected in symptomatic individuals, whether newborns or adults, diagnosis involves laboratory tests on specific bodily fluids. For newborns showing symptoms, doctors may collect samples of blood or cerebrospinal fluid (obtained via a spinal tap). These samples are then cultured to confirm the presence of Streptococcus agalactiae.
Similarly, in adults with suspected infections, samples such as blood or urine are collected for laboratory analysis. Identifying the bacteria from these normally sterile sites helps confirm an active infection and guides appropriate treatment.
Treatment and Prevention
Preventing GBS infection in newborns is primarily achieved through intrapartum antibiotic prophylaxis (IAP). This involves administering intravenous (IV) antibiotics to a GBS-positive pregnant individual during labor. Penicillin G is the preferred antibiotic, with ampicillin as an acceptable alternative.
The antibiotics are most effective when given at least four hours before delivery, as this allows sufficient time for the medication to reach adequate levels in the mother and potentially the fetal circulation. This preventative measure significantly reduces the risk of GBS transmission from mother to newborn during birth.
For active GBS infections, prompt medical treatment with antibiotics is generally administered. Penicillin or ampicillin are commonly used due to GBS’s uniform susceptibility to these medications. For individuals with penicillin allergies, alternative antibiotics like cefazolin, clindamycin, or vancomycin may be used, depending on the severity of the allergy and bacterial susceptibility.
Early initiation of antibiotics is important for newborns with suspected or confirmed GBS disease to manage the infection effectively and improve outcomes. The specific antibiotic regimen and duration of treatment are determined by the severity and location of the infection.