Strep throat is an infection caused by the bacterium Group A Streptococcus (GAS), or Streptococcus pyogenes. While initial symptoms like a sore throat and fever are painful, they are typically treatable with a simple course of antibiotics. Treatment prevents the bacteria from causing severe health consequences that extend far beyond the initial infection. Untreated, the bacteria can spread locally or trigger a misguided autoimmune response in distant organs, potentially leading to lifelong conditions. Although acute symptoms may fade, the untreated GAS bacteria remain a threat, capable of initiating inflammatory and destructive processes in the body.
Acute Localized Complications
When the Group A Streptococcus infection is left unchecked, it may spread beyond the tonsils and pharynx to adjacent anatomical structures, leading to suppurative (pus-forming) complications. This localized spread can result in a peritonsillar abscess, a collection of pus behind one of the tonsils. This condition causes severe throat pain, difficulty swallowing, and often requires surgical drainage along with intensive antibiotic therapy.
The infection may also travel through the Eustachian tubes, causing acute otitis media (ear infection), or ascend into the paranasal sinuses, resulting in acute sinusitis. These localized extensions prolong the illness, intensify symptoms, and may necessitate more involved medical or surgical procedures.
The Risk of Rheumatic Fever
One of the most concerning long-term consequences of untreated GAS pharyngitis is Acute Rheumatic Fever (ARF), an inflammatory disorder that typically begins two to four weeks after the initial infection. ARF is an autoimmune response triggered by molecular mimicry, not by the bacteria directly attacking the organs. The immune system creates antibodies to fight the Streptococcus pyogenes M protein, which structurally resembles proteins found in human tissues, particularly those in the heart, joints, brain, and skin.
This cross-reactivity causes the antibodies to mistakenly attack the body’s own healthy tissues. The most devastating manifestation of ARF is carditis, which involves inflammation and damage to the heart, often targeting the mitral and aortic valves.
Repeated or severe attacks of ARF can lead to permanent scarring and deformation of the heart valves, known as Rheumatic Heart Disease (RHD). RHD can result in lifelong cardiac issues, including heart failure, as damaged valves may leak or become narrowed (stenosis). Prompt antibiotic treatment remains a standard preventative measure, as therapy given within nine days of symptom onset can prevent ARF development.
Delayed Impact on Kidney Function
Another serious, non-suppurative complication of untreated strep throat is Post-streptococcal Glomerulonephritis (PSGN), which affects the kidneys. PSGN is an inflammatory condition that targets the glomeruli, the tiny filtering units within the kidneys. This condition typically appears about ten days after the onset of strep throat symptoms.
The mechanism involves the formation of immune complexes made up of streptococcal antigens and the body’s antibodies. These complexes circulate in the bloodstream and become trapped in the glomeruli, where they trigger an inflammatory response. The resulting damage to the filters can cause symptoms like dark, reddish-brown urine due to the presence of blood, and edema (swelling), particularly around the face and eyes.
Most individuals, especially children, recover fully from PSGN within a few weeks, making the long-term prognosis generally favorable. However, the condition can cause temporary hypertension and, in rare instances, progress to chronic kidney disease or kidney failure. Unlike Acute Rheumatic Fever, antibiotic treatment of the initial strep throat infection has not been shown to prevent PSGN development.
Life-Threatening Systemic Infection
In rare but severe cases, the Group A Streptococcus bacteria can invade deep tissues and the bloodstream, leading to life-threatening systemic infections. This invasive group A streptococcal (iGAS) disease occurs when the bacteria spread to parts of the body where they are not normally found. Two of the most aggressive forms are Streptococcal Toxic Shock Syndrome (STSS) and Necrotizing Fasciitis.
STSS is a rapidly progressing condition caused by the bacteria releasing powerful toxins (superantigens) into the bloodstream. These toxins trigger a massive immune response that leads to plummeting blood pressure and multi-organ failure, affecting the kidneys and liver. Even with immediate medical intervention, the mortality rate for STSS is high, often approaching 30%.
Necrotizing Fasciitis is an infection that rapidly destroys the soft tissue and fascia, the connective tissue surrounding muscles. While it often begins at a wound site, it can arise from a GAS infection that has spread from the throat. This medical emergency requires immediate surgery to remove the dead tissue, in addition to powerful antibiotics, and it carries a high risk of death.