Group A Streptococcus (GAS) is the bacterium responsible for the highly contagious infection known as strep throat. This infection is straightforward to diagnose and easily treatable with a short course of antibiotics, primarily penicillin or amoxicillin. When the infection is left untreated, the bacteria can persist, leading to severe complications that affect distant organs. These serious health issues are often triggered by the body’s immune reaction to the lingering bacteria, rather than the infection itself.
Localized Infections and Abscess Formation
When the bacterial infection is not cleared, it can spread into the tissues surrounding the tonsils and throat, resulting in localized pus-filled pockets. The most common severe outcome is a peritonsillar abscess, often called Quinsy, which forms between the tonsil and the muscular wall of the throat. This collection of pus causes intense, unilateral throat pain and significant swelling, making swallowing and speaking difficult.
An untreated abscess can grow large enough to push the tonsil toward the midline, potentially obstructing the airway and creating a life-threatening emergency. The infection can also spread to neighboring structures in the head and neck. Bacteria traveling through the eustachian tubes may cause a middle ear infection (otitis media), or lead to inflammation of the sinuses (sinusitis) and, rarely, the mastoid bone behind the ear (mastoiditis).
The Risk of Rheumatic Fever
Acute rheumatic fever (RF) is an autoimmune disease that typically emerges two to four weeks after the initial sore throat resolves. RF is caused by a misdirected immune response known as molecular mimicry, not by the bacteria invading the organs. The immune system generates antibodies to fight the strep bacteria, specifically targeting the M protein on the bacterial surface.
The structure of the M protein closely resembles certain proteins found in human tissue, such as cardiac myosin, a component of the heart muscle. The antibodies created to neutralize the bacteria mistakenly recognize these host proteins and launch an attack on the body’s own tissues. This autoimmune assault leads to inflammation in several areas, including the joints, skin, and nervous system.
The most serious long-term damage occurs in the heart, a condition known as rheumatic heart disease (RHD). Inflammation of the heart tissue, or carditis, commonly affects the heart valves. Repeated inflammation causes scarring and thickening of the heart valves, preventing them from opening and closing properly. This damage can be permanent, potentially requiring surgical valve repair or replacement.
Delayed Damage to Kidneys and Brain
An untreated Group A Strep infection can trigger systemic immune responses affecting the kidneys and the brain. Post-Streptococcal Glomerulonephritis (PSGN) is an inflammatory condition of the kidneys that occurs one to two weeks after infection. This condition is caused by immune complexes—clumps of strep antigens bound to antibodies—that circulate in the bloodstream and become lodged in the tiny filtering units of the kidneys, called glomeruli.
This immune complex deposition damages the glomeruli, reducing the kidneys’ ability to filter waste and excess fluid from the blood. Symptoms include blood in the urine (often dark or smoky) and edema, or swelling, particularly noticeable around the eyes and face. Although most children recover fully from PSGN, the condition can lead to high blood pressure and, in rare instances, long-term kidney damage or failure, particularly in adults.
A separate, though sometimes controversial, neurological complication is Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS). In PANDAS, the immune response to the strep infection is thought to target the basal ganglia, a region deep within the brain that controls movement and behavior.
The signature feature of PANDAS is the sudden, acute onset of obsessive-compulsive disorder (OCD) or severe tic disorders. Additional symptoms can include severe separation anxiety, mood swings, and deterioration in fine motor skills, such as handwriting.