Is strep throat a viral or bacterial infection?

Strep Throat is a Bacterial Infection

Strep throat is definitively a bacterial infection caused by Group A β-hemolytic streptococcus (Streptococcus pyogenes), not a viral infection. 1

Causative Agent and Definition

Strep throat, also known as streptococcal pharyngitis, is an acute infection of the oropharynx and/or nasopharynx specifically caused by Streptococcus pyogenes, which is a Group A β-hemolytic streptococcus (GABHS) 1. This bacterial pathogen is the most common bacterial cause of acute pharyngitis, though it only accounts for a minority of all sore throat cases 1.

Differentiating Bacterial vs. Viral Pharyngitis

It's important to understand that while strep throat is bacterial, most cases of pharyngitis (sore throat) are actually viral in origin:

• Bacterial (Strep) Pharyngitis:

  • Accounts for 5-15% of adult and 15-35% of pediatric pharyngitis cases 2
  • Caused by Group A streptococcus
  • Requires antibiotic treatment
  • Characteristic features include sudden onset of sore throat, fever, pain on swallowing, tonsillopharyngeal erythema with or without exudates, and tender enlarged anterior cervical lymph nodes 1

• Viral Pharyngitis:

  • Most common cause of sore throat
  • Caused by respiratory viruses (adenovirus, parainfluenza, rhinovirus, etc.)
  • Does not respond to antibiotics
  • Often accompanied by symptoms like cough, hoarseness, coryza, conjunctivitis, and diarrhea 1

Diagnostic Approach

Because the clinical symptoms of streptococcal and viral pharyngitis overlap significantly, laboratory testing is necessary for definitive diagnosis:

1. Throat culture: Remains the gold standard for diagnosis with 90-95% sensitivity 1
2. Rapid antigen detection tests (RADT): Provides quick results but may be less sensitive than culture 1

Clinical Significance and Treatment

The importance of correctly identifying strep throat lies in its potential complications and appropriate treatment:

• Complications if untreated:

  • Suppurative complications: peritonsillar abscess, cervical lymphadenitis, mastoiditis 1
  • Non-suppurative complications: acute rheumatic fever, acute glomerulonephritis 1

• Treatment:

  • Penicillin remains the treatment of choice due to its proven efficacy, safety, narrow spectrum, and low cost 1, 3
  • Erythromycin is recommended for patients allergic to penicillin 1
  • Treatment duration is typically 10 days to optimize cure 4

Common Pitfalls

1. Misdiagnosis based on clinical features alone: Physicians often overdiagnose streptococcal pharyngitis based solely on symptoms, leading to unnecessary antibiotic use 4

2. Failure to test: Without laboratory confirmation, it's difficult to differentiate between viral and bacterial causes 1

3. Inappropriate antibiotic use: Treating viral pharyngitis with antibiotics contributes to antibiotic resistance without providing benefit 1

In conclusion, while most sore throats are viral in origin, strep throat specifically refers to pharyngitis caused by Group A streptococcus bacteria and requires appropriate antibiotic treatment to prevent complications and reduce transmission.