Streptococcus are common bacteria that can reside harmlessly in the human body or cause infections. Group A Streptococcus (Strep A) and Group B Streptococcus (Strep B) are two notable types often associated with human health concerns. Understanding their distinctions is important, as they typically cause different types of infections and affect different populations.
Group A Streptococcus (Strep A)
Group A Streptococcus, scientifically known as Streptococcus pyogenes, is a bacterium commonly found in the throat and on the skin. This highly contagious bacterium spreads primarily through respiratory droplets, such as those released when an infected person talks, coughs, or sneezes. Direct contact with secretions from an infected individual, like saliva or wound discharge, can also transmit the bacteria.
Strep A is responsible for various infections, ranging from mild to severe. Common mild infections include strep throat (pharyngitis), characterized by a sudden sore throat, fever, and sometimes white patches on the tonsils. Scarlet fever, which typically follows strep throat and presents with a red rash that feels like sandpaper, and skin infections like impetigo, causing itchy, fluid-filled blisters, are also frequently caused by Strep A, especially in children. Strep A infections are most common among children aged 5 to 15 years, although adults can also be affected.
More severe, though rare, infections caused by Strep A are classified as invasive Group A Streptococcal (iGAS) diseases. These occur when the bacteria enter deep tissues or organs, potentially leading to life-threatening conditions. Examples include necrotizing fasciitis, a rapidly progressing infection that destroys tissue, and streptococcal toxic shock syndrome, where toxins produced by the bacteria cause organs to malfunction. These severe infections are more likely in individuals with chronic illnesses or breaks in the skin.
Group B Streptococcus (Strep B)
Group B Streptococcus, or Streptococcus agalactiae, is a bacterium often found in the gastrointestinal tract and, in women, the vagina. Many healthy individuals can carry Strep B without experiencing any symptoms or illness. The exact mechanisms of how Strep B spreads among adults are not entirely clear, but it is not typically transmitted through sexual contact, food, or water.
Strep B is particularly significant in pregnant women and newborns. Pregnant individuals may carry the bacteria in their bodies, and it can be passed to the baby during a vaginal delivery. While most babies exposed to Strep B remain healthy, some can develop serious infections, often within the first week of life, known as early-onset disease. These infections can include neonatal sepsis (a bloodstream infection), meningitis (inflammation of the membranes around the brain and spinal cord), and pneumonia. Symptoms in newborns might include fever, feeding difficulties, breathing problems, or unusual sluggishness.
Strep B can also cause infections in adults, especially those who are elderly, have weakened immune systems, or underlying health conditions like diabetes. In these adult populations, Strep B can lead to urinary tract infections, skin infections, bloodstream infections (sepsis), and pneumonia.
Key Differences in Presentation and Spread
Strep A primarily causes throat and skin infections, spreading through respiratory droplets and direct contact. Strep B’s main concern is its impact on newborns and vulnerable adults, spreading through vertical transmission from mother to baby during birth. For adults, Strep B often colonizes the gastrointestinal or genital tracts.
Diagnosis and Treatment Approaches
Diagnosing Strep A and Strep B involves different methods tailored to their common infection sites and populations. For Strep A throat infections, a rapid strep test is often the initial diagnostic tool, providing quick results by detecting specific bacterial antigens. If the rapid test is negative, especially in children, a throat culture may be performed for confirmation, as it is considered the gold standard for accuracy but takes 24-48 hours for results. Skin infections caused by Strep A are typically diagnosed through clinical examination and bacterial culture from the lesion.
For Strep B, routine screening is performed for pregnant women, typically between 35 and 37 weeks of pregnancy. This involves swabbing the vagina and rectum, with samples sent to a lab for culture. A positive screening indicates the presence of the bacteria but does not necessarily mean the mother or baby will become sick. If a newborn is suspected of having a Strep B infection, samples of their blood or spinal fluid are tested for the bacteria.
Both Strep A and Strep B infections are bacterial and are treated with antibiotics. For Strep A infections, penicillin or amoxicillin are the antibiotics of choice, typically prescribed for a 10-day course. These antibiotics are effective in preventing complications like acute rheumatic fever. For individuals with penicillin allergies, alternative antibiotics like cephalexin, clindamycin, or azithromycin may be used.
In the case of Strep B, if a pregnant woman tests positive, intravenous (IV) antibiotics, usually penicillin, are administered during labor to reduce the risk of transmission to the baby. This is most effective when given at least four hours before delivery. For newborns or adults who develop Strep B infections, antibiotics are also used, with penicillin being a common choice. Completing the full course of antibiotics is important for both types of infections to ensure complete eradication of the bacteria and prevent recurrence or complications.