Group G Streptococcus (GGS) is a bacterium often associated with mild infections, but it has the capacity to cause severe, potentially life-threatening illness. The scientific name for the strain most commonly responsible for human infections is Streptococcus dysgalactiae subspecies equisimilis. While many people carry this organism without symptoms, its ability to invade the bloodstream means it can pose a significant danger, especially to vulnerable populations.
Understanding Group G Streptococcus
Group G Streptococcus is categorized using the Lancefield classification system, which groups streptococcal bacteria based on specific carbohydrates on their cell walls. The human-adapted strain, S. dysgalactiae subsp. equisimilis, is closely related to the more widely known Group A Streptococcus (GAS), or S. pyogenes. Like GAS, GGS is a beta-hemolytic bacterium, meaning it completely breaks down red blood cells when grown in culture.
This organism frequently exists as a harmless colonizer of the human body, often found on the skin, in the throat, and within the gastrointestinal and female genital tracts. A break in these barriers provides an easy entry point for infection. GGS shares several virulence factors with GAS, including toxins and enzymes that help it evade the immune system and spread through tissue.
Common Infections Caused by Strep G
The most frequent clinical presentations of Group G Streptococcus infection involve the throat and the skin. GGS is a recognized cause of pharyngitis, or “strep throat,” though it is less common than pharyngitis caused by Group A Streptococcus. Symptoms are similar to other forms of strep throat, including a sore throat, fever, and swollen lymph nodes.
Skin and soft tissue infections represent the other primary manifestation of GGS disease. These include cellulitis, a common bacterial skin infection causing redness, swelling, and pain. GGS also causes erysipelas and impetigo, which are more superficial skin infections. Non-invasive cases are usually localized and respond well to standard antibiotic treatment.
Factors Leading to Severe or Invasive Disease
The designation “invasive” applies when GGS enters a normally sterile site in the body, such as the bloodstream, causing Invasive Group G Streptococcal Disease (iGGSD). This serious form of infection closely mirrors the severe diseases caused by Group A Streptococcus. While rare in healthy individuals, iGGSD is associated with a case fatality rate reported to be between 15 and 18% in cases involving bloodstream infection.
The risk of developing iGGSD increases significantly in individuals with certain underlying medical conditions. Advancing age is a major factor, with the elderly being disproportionately affected by invasive GGS infections. Chronic diseases that compromise the immune system or create skin integrity issues also raise the risk.
Specific conditions often linked to iGGSD include diabetes mellitus, chronic liver disease, and immunosuppression from medications or diseases. Other predisposing factors include any condition that causes skin breakdown, such as chronic venous stasis ulcers. The most severe outcomes of iGGSD are bacteremia, endocarditis, and septic arthritis.
The bacterium can also cause devastating soft-tissue infections, including necrotizing fasciitis (“flesh-eating disease”) and streptococcal toxic shock syndrome. Necrotizing fasciitis is a rapidly progressing infection of the deeper layers of skin and tissue requiring immediate surgical intervention and intensive care. Streptococcal toxic shock syndrome is a systemic response to bacterial toxins that can lead to rapid organ failure and low blood pressure.
Diagnosis and Management
Diagnosing a Group G Streptococcus infection begins with identifying the organism from a clinical sample, such as a throat swab, wound culture, or blood culture. Laboratory identification typically involves culturing the bacteria and using techniques like Lancefield grouping or molecular methods such as PCR. The organism is confirmed as a beta-hemolytic streptococcus that reacts with Group G antisera.
The standard treatment for GGS infections is a course of antibiotics, with penicillin or amoxicillin being the preferred choices due to the organism’s high susceptibility. For severe invasive infections like bacteremia or necrotizing fasciitis, intravenous antibiotics are necessary, sometimes combined with other agents like clindamycin if toxic shock syndrome is suspected. Early diagnosis and prompt antibiotic administration are particularly important for high-risk patients to prevent the progression to severe invasive disease.