Complications of Untreated Group A Streptococcus Infection
Untreated Group A Streptococcus (GAS) infection can lead to serious suppurative complications (abscess formation, invasive disease) and life-threatening nonsuppurative immune-mediated sequelae including acute rheumatic fever, post-streptococcal glomerulonephritis, and rarely pulmonary-renal syndrome.
Major Complications
Nonsuppurative (Immune-Mediated) Complications
These are the most clinically significant complications that justify antibiotic treatment:
Acute Rheumatic Fever (ARF): The most important immune-mediated complication historically, though now rare in developed countries due to decreased circulation of rheumatogenic GAS strains 1. This remains a critical concern in certain geographic areas and populations 2.
Post-Streptococcal Glomerulonephritis (PSGN): Causes rapidly progressive kidney disease with hematuria and renal dysfunction 3, 4. Can occur 1-3 weeks after pharyngeal or skin infection 5.
Pulmonary-Renal Syndrome (PRS): An extremely rare but potentially fatal complication characterized by diffuse alveolar hemorrhage and rapidly progressive glomerulonephritis 6. Only six cases of streptococcal-induced PRS have been documented, with high mortality rates requiring immediate pulse steroids and plasmapheresis 6.
Suppurative (Direct Infection) Complications
- Peritonsillar or retropharyngeal abscess: Local extension of pharyngeal infection
- Invasive GAS (iGAS) disease: Including necrotizing fasciitis, streptococcal toxic shock syndrome, and bacteremia 4, 7
- Compartment syndrome: Rare but documented cases requiring emergency surgical decompression 8
Important Clinical Context
The actual preventable burden is surprisingly low. Recent 2026 Swedish population data demonstrates that even with universal throat swabbing and antibiotic treatment of all GAS-positive patients, only 6.7% of invasive GAS cases in children and 2.8% in adults could be prevented 9. The number needed to treat to prevent one invasive GAS case ranges from 12,000-110,000 patients 9.
Key Caveats
- Most nonsuppurative complications (ARF, PSGN) develop from the immune response and may occur even with appropriate antibiotic treatment if started late in the disease course
- The risk of ARF has dramatically decreased in developed nations, likely due to changes in circulating GAS strain virulence rather than antibiotic use alone 1
- Treatment is still indicated because when complications do occur, they can be devastating (rheumatic heart disease, renal failure, death from invasive disease)
High-Risk Situations Requiring Vigilance
Per IDSA guidelines 2, special attention to treatment and potential carrier eradication is warranted during:
- Community outbreaks of ARF, PSGN, or invasive GAS
- Patients with personal or family history of ARF
- Closed community outbreaks (schools, military barracks)
The rationale for treating GAS pharyngitis remains valid despite low absolute risk reduction, as the potential complications—though rare—carry significant morbidity and mortality 4, 5.