Strep throat, a common bacterial infection, is caused by Streptococcus pyogenes, also known as Group A Streptococcus (GAS). While the initial illness is uncomfortable, characterized by a sudden sore throat, fever, and difficulty swallowing, it is highly treatable with antibiotics. The danger of a strep infection lies not in the acute phase, but in the serious, non-infectious complications that arise if the bacteria persists. These delayed sequelae involve the immune response mistakenly attacking the body’s own tissues, leading to damage in the heart and kidneys.
Acute Disease Progression and Local Spread
If strep throat is not treated, the bacterial population multiplies, worsening acute symptoms like pain and fever. The individual remains highly contagious for a longer period, sometimes several weeks, posing a risk to others. The bacteria can spread from the throat to adjacent tissues, leading to suppurative complications.
A localized complication is a peritonsillar abscess (quinsy), where a pocket of pus forms behind a tonsil, causing severe throat pain and difficulty opening the mouth. The infection may also track into the middle ear (otitis media) or into the sinus cavities (sinusitis). More rare but serious localized infections include retropharyngeal abscesses, which are deep neck infections that can compress the airway. These spreading infections require medical intervention, often involving surgical drainage in addition to antibiotics.
Systemic Autoimmune Damage: Rheumatic Fever
The most serious complication of untreated strep throat is Acute Rheumatic Fever (ARF), a delayed inflammatory condition resulting from an autoimmune reaction. ARF develops when the immune system, generating antibodies to fight the strep bacteria, mistakenly attacks the body’s own proteins. This phenomenon, known as molecular mimicry, occurs because certain GAS proteins, particularly the M protein, share structural similarities with human tissues.
These cross-reactive antibodies and T-cells can target the joints, brain, skin, and the heart. The resulting inflammation in the heart is called carditis, which damages the heart valves, leading to Rheumatic Heart Disease (RHD). The mitral and aortic valves are most commonly affected, where inflammation causes scarring and deformation that permanently impairs their function.
Rheumatic fever can manifest as migratory polyarthritis, characterized by painful, transient inflammation that moves between joints without causing permanent damage. Neurological involvement can appear as Sydenham chorea, an involuntary movement disorder reflecting inflammation in the basal ganglia. The heart damage is chronic and progressive, often requiring long-term monitoring and sometimes valve replacement surgery.
Kidney Complications: Post-Streptococcal Glomerulonephritis
Another serious, non-suppurative complication is Post-Streptococcal Glomerulonephritis (PSGN), which affects the kidneys’ filtering units, the glomeruli. PSGN is an immune-mediated condition that emerges about 10 days following a strep throat infection. The mechanism involves the formation of immune complexes (clumps of strep antigens bound to antibodies) that circulate in the bloodstream.
These immune complexes become trapped within the glomeruli, triggering an inflammatory response that damages the filtering structures. Symptoms of PSGN include hematuria (visible blood in the urine, which appears dark or rust-colored) and edema (swelling often seen in the face, hands, and feet). High blood pressure (hypertension) and decreased urine output are common signs of impaired kidney function.
Most children recover fully from PSGN, but the condition can, in rare instances, lead to acute renal failure or long-term kidney damage, especially in adults. Unlike Rheumatic Fever, antibiotic treatment of the initial strep infection may not always prevent the development of PSGN. The condition is a Type III hypersensitivity reaction, meaning the damage is caused by the immune response itself, not the direct bacterial infection of the kidneys.
The Necessity of Prompt Diagnosis and Treatment
Given the risk of severe, long-term complications, rapid diagnosis of strep throat is necessary. Diagnosis is confirmed using a rapid strep test or a throat culture. Once Group A Streptococcus is identified, treatment involves a course of antibiotics, usually penicillin or amoxicillin, which are effective against this bacteria.
Starting antibiotic treatment within the first nine days of illness reduces the risk of developing Acute Rheumatic Fever. The medication eliminates the bacteria from the throat, limiting the exposure that triggers the autoimmune response. Patients become non-contagious after 24 hours of antibiotic therapy, allowing for a quicker return to normal activities.
The full course of antibiotics must be completed, even if symptoms improve quickly, to ensure complete eradication of the bacteria. Failure to complete the prescribed regimen may allow bacteria to survive, potentially leading to recurrence or increasing the risk of delayed, autoimmune sequelae. Prompt, full treatment prevents the cascade of events that can result in permanent damage to the heart and other organ systems.