Strep throat is a highly contagious bacterial infection caused by Streptococcus pyogenes, commonly known as Group A Streptococcus (GAS). This infection primarily causes pharyngitis, or inflammation of the throat, often leading to a sudden, painful sore throat and fever. While symptoms may sometimes improve naturally within a few days, the danger of untreated strep throat lies in the bacterial presence remaining long enough to trigger severe, delayed reactions. These complications range from localized tissue destruction to systemic, long-term damage to the heart and kidneys.
Immediate Local Complications
If Streptococcus pyogenes bacteria are left unchecked, they can spread directly into the surrounding tissues. This localized invasion leads to complications that represent a worsening of the acute illness. The bacteria can form a peritonsillar abscess (quinsy), a collection of pus next to the tonsils, marked by severe throat pain, difficulty swallowing (dysphagia), and a muffled voice.
A less common, but more serious, localized complication is a retropharyngeal abscess, where the infection spreads to the deep tissues at the back of the throat. This abscess can be life-threatening if it obstructs the airway, requiring immediate medical intervention and drainage. The infection can also cause cervical lymphadenitis, a painful swelling of the lymph nodes in the neck. These local complications often require hospitalization and surgical drainage in addition to antibiotic therapy.
Autoimmune Damage to the Heart and Joints
The most severe, delayed consequence of untreated strep throat is Acute Rheumatic Fever (ARF), a systemic inflammatory condition that develops two to four weeks after the initial infection. ARF is caused by an abnormal immune response known as molecular mimicry, where antibodies generated to fight the bacteria mistakenly attack the body’s own tissues.
The heart is particularly vulnerable, leading to rheumatic heart disease. Antibodies cross-react with proteins in the heart valves, causing inflammation (carditis) and permanent scarring. This damage impairs the valves’ ability to open and close properly, and long-term valve damage can progress to heart failure.
The body’s joints are also a common target, resulting in migratory polyarthritis. This involves painful inflammation that rapidly moves from one large joint—like the knees, ankles, or elbows—to another. In some cases, the central nervous system is affected, causing Sydenham’s Chorea, characterized by involuntary, jerky movements and emotional lability.
Impact on Kidney Function
Another major systemic complication is Post-Streptococcal Glomerulonephritis (PSGN), which affects the filtering units of the kidneys. This condition typically appears about 10 days after the throat infection. PSGN results when immune complexes—clusters of antibodies bound to streptococcal antigens—become lodged in the glomeruli, the tiny blood vessels responsible for filtering waste.
The trapping of these complexes triggers an inflammatory response within the kidney filters, impairing their function. This damage often presents with symptoms like hematuria (dark, tea-colored urine) and edema, or swelling, particularly around the eyes and face. While PSGN often resolves completely, the damage can occasionally lead to long-term chronic kidney disease.
The Importance of Timely Diagnosis and Antibiotics
The serious, delayed consequences of strep throat are almost entirely preventable through timely antibiotic treatment. Diagnosis begins with either a rapid antigen detection test (RADT) or a throat culture to confirm the presence of Streptococcus pyogenes bacteria. Once confirmed, a 10-day course of antibiotics, typically penicillin or amoxicillin, is prescribed to eliminate the bacterial threat.
This treatment is most effective at preventing severe systemic complications like ARF and PSGN if initiated promptly. Antibiotics reduce the risk of ARF if started within nine days of the onset of illness. It is important to complete the entire 10-day course, even if symptoms improve quickly, to ensure all bacteria are eradicated and prevent recurrence. Timely antibiotic use also significantly reduces the risk of transmission to others.