Strep throat is a common infection of the throat and tonsils caused by Group A Streptococcus (Streptococcus pyogenes). Although antibiotics make it a highly treatable illness, the danger is directly linked to delayed or absent treatment. Allowing the bacteria to persist in the body can trigger a cascade of severe complications, ranging from localized infections to debilitating, long-term autoimmune diseases. Treating the infection within the first nine days is the primary method for preventing these serious post-infection consequences.
Local Spread and Immediate Infections
If the Group A Streptococcus bacteria are not eliminated, they can proliferate and invade the tissues immediately surrounding the initial site of infection. This direct spread often leads to the formation of a peritonsillar abscess, a pocket of pus that develops next to one of the tonsils. This abscess causes extreme throat pain, often concentrated on one side, and can make it nearly impossible to swallow or open the mouth completely.
The expanding infection can also travel through the body’s connected passages to adjacent structures. Bacteria migrating into the middle ear space can cause otitis media, which is an ear infection characterized by pain and pressure. Similarly, the bacteria may spread into the sinus cavities, resulting in sinusitis, an inflammation that causes facial pain and thick nasal discharge. While generally less severe than systemic issues, these local infections can lead to significant discomfort and, in the case of a large peritonsillar abscess, potentially obstruct the airway.
Systemic Damage to the Heart and Joints
One of the most concerning outcomes of an untreated strep infection is the development of Acute Rheumatic Fever (RF), a delayed inflammatory reaction. This condition is not caused by the bacteria themselves, but rather by an autoimmune response where the body’s own defenses turn against healthy tissue. The immune system produces antibodies to attack the streptococcal bacteria, but due to a phenomenon called molecular mimicry, these antibodies mistakenly recognize and attack proteins in the heart, joints, skin, and brain.
The resulting inflammation in the joints causes migratory arthritis, which presents as painful swelling that moves from one large joint to another. A far more serious consequence is carditis, or inflammation of the heart muscle and valves. Inflammation of the heart valves, particularly the mitral valve, can lead to scarring and permanent damage over time, a condition known as Rheumatic Heart Disease (RHD). This irreversible damage weakens the valves, impairing the heart’s pumping efficiency and potentially leading to heart failure.
Acute Post-Streptococcal Glomerulonephritis
Another major post-streptococcal inflammatory condition is Acute Post-Streptococcal Glomerulonephritis (APSGN), which targets the kidneys. This complication involves inflammation of the glomeruli, the small filtering units within the kidneys responsible for removing waste and excess fluid from the blood. The mechanism differs slightly from Rheumatic Fever, as it is primarily caused by immune complexes—clumps of strep antigens and antibodies—that circulate in the bloodstream and become trapped in the kidney filters.
The blockage and damage to the glomeruli impairs the kidney’s ability to function properly, leading to noticeable symptoms. Patients often experience hematuria (blood in the urine), which may appear dark or tea-colored, along with edema (swelling), particularly around the face and ankles. Hypertension (high blood pressure) is also common due to the body retaining excess fluid. While the prognosis for children with APSGN is generally favorable with full recovery, adults face a higher risk of persistent issues and potential long-term kidney failure.
Autoimmune Effects on the Brain
A less common but highly specific neurological complication primarily affecting children is Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections (PANDAS). This condition is characterized by the abrupt, dramatic onset or worsening of Obsessive-Compulsive Disorder (OCD) symptoms or tic disorders following a strep infection. The proposed biological cause is similar to Rheumatic Fever, involving an autoimmune reaction where antibodies cross-react with cells in a specific area of the brain called the basal ganglia.
The inflammation in the basal ganglia is thought to cause the sudden and severe behavioral changes. These symptoms can be debilitating, often appearing overnight and including emotional lability, separation anxiety, and motor hyperactivity. Recognizing this sudden onset in association with a preceding strep infection is important, as timely antibiotic treatment is the only measure proven to prevent the development of all the serious local and systemic complications discussed.