Strep throat is a common bacterial infection caused by Streptococcus pyogenes, also known as Group A Streptococcus (GAS). While initial symptoms include pain and fever, the true hazard lies in the potential for delayed, systemic complications. If left unchecked, the body’s response to the bacteria can trigger inflammatory and autoimmune reactions that extend far beyond the tonsils. Completing a full course of antibiotic treatment is the standard of care because it prevents the onset of these long-term health issues. The bacteria must be eliminated quickly to interrupt the cascade of events that can lead to permanent damage in distant organs.
Local Progression and Acute Spread
When a Group A Streptococcus infection is not treated, the bacteria may multiply and spread to adjacent tissues in the head and neck. This localized progression can lead to severe, acute complications requiring immediate medical or surgical intervention. A common example is a peritonsillar abscess, often called Quinsy, where a pocket of pus forms behind the tonsil, causing difficulty swallowing and a muffled voice.
The infection can also spread through the Eustachian tubes, causing acute otitis media (middle ear infection). Similarly, the bacteria may spread into the sinus cavities, resulting in bacterial sinusitis, characterized by facial pain and thick discharge.
A more serious development is a deep neck infection, such as a retropharyngeal or parapharyngeal abscess. These abscesses form in the deep spaces of the neck and can rapidly swell to compress the airway, posing an immediate threat to breathing. These deep-seated infections represent a time-sensitive, life-threatening consequence of unchecked bacterial multiplication.
Risk of Rheumatic Fever and Cardiac Damage
The most severe consequence of untreated strep throat is Acute Rheumatic Fever (ARF), an inflammatory condition resulting from the body’s misdirected immune response. This systemic autoimmune reaction typically begins two to four weeks after the initial throat infection has resolved. Antibodies produced to fight the GAS bacteria mistakenly cross-react with the body’s own proteins, a phenomenon known as molecular mimicry.
The inflammation from ARF can affect various connective tissues, including the joints, skin, and brain. Its greatest long-term impact is on the heart, where the autoimmune attack targets the tissue and valves, a condition called carditis. This inflammation leads to permanent scarring and damage, resulting in Rheumatic Heart Disease (RHD).
RHD primarily damages the heart valves, most commonly the mitral valve, which controls blood flow between the heart’s upper and lower left chambers, and often the aortic valve as well. The inflammation causes the valve leaflets to become rigid, thickened, or fused, leading to either stenosis (narrowing) or regurgitation (leaky flow). This mechanical failure forces the heart to work harder, eventually leading to a permanent decline in cardiac function and chronic heart failure later in life.
ARF can also cause migratory polyarthritis, a painful swelling that rapidly moves between large joints like the knees or ankles. Another manifestation is Sydenham chorea, a neurological disorder characterized by involuntary, jerky movements affecting the brain’s basal ganglia. Cumulative damage from recurrent episodes of ARF makes RHD the leading cause of acquired heart disease globally.
Renal and Neurological Complications
Post-Streptococcal Glomerulonephritis (PSGN)
Post-Streptococcal Glomerulonephritis (PSGN) affects the filtering units of the kidneys. This condition develops through an immune mechanism similar to ARF, typically appearing ten days to three weeks following the initial infection. PSGN is an immune complex-mediated disease where complexes of streptococcal antigens and antibodies become trapped in the glomeruli, impairing the kidneys’ ability to filter waste.
The resulting inflammation leads to symptoms of nephritic syndrome. Patients often experience hematuria, visible as dark, “cola-colored” urine, due to blood leaking through the damaged filters. Fluid retention causes edema, particularly puffiness around the eyes, and can lead to elevated blood pressure (hypertension). While PSGN often resolves completely, a small number of patients can develop acute kidney injury or progress to chronic kidney disease.
PANDAS and Invasive Infection
The neurological system can be affected by the immune aftermath of Group A Streptococcus through Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections (PANDAS). This condition is characterized by the sudden onset or worsening of Obsessive-Compulsive Disorder (OCD) symptoms or tic disorders in children. PANDAS involves an autoimmune attack where anti-streptococcal antibodies mistakenly target the basal ganglia of the brain, leading to abrupt behavioral changes often occurring within days of a strep infection.
The unchecked bacterial infection can also progress to life-threatening invasive Group A Streptococcal (iGAS) disease. This occurs when the bacteria penetrate deep, normally sterile tissue layers, leading to conditions such as streptococcal toxic shock syndrome (STSS) or necrotizing fasciitis. STSS is a rapidly progressing illness involving high fever, low blood pressure, and multi-organ failure. Necrotizing fasciitis is a severe, rapidly spreading infection that destroys soft tissue. These invasive infections have mortality rates ranging from 30% to 60% even with aggressive hospital treatment.