How to manage persistently elevated Antistreptolysin O (ASO) titers?

Management of Persistently Elevated Antistreptolysin O (ASO) Titers

Persistently elevated ASO titers alone do not require treatment in most cases, as carriers of Group A Streptococci (GAS) are at little to no risk for developing complications and are unlikely to spread the organism to close contacts. 1

Understanding ASO Titers and Their Significance

ASO titers reflect a previous streptococcal infection, not necessarily an active one. They begin to rise approximately 1 week after infection and peak between 3-6 weeks post-infection 2. Normal values vary by age, with higher values in children than adults 2.

Key points about ASO titers:

• They indicate recent past infection rather than current active infection 2
• Persistently elevated titers may represent:
  • Chronic GAS pharyngeal carriage with intercurrent viral infections 1
  • Recent but resolved GAS infection 2
  • Ongoing immune response without active infection

Diagnostic Approach for Persistently Elevated ASO

When faced with persistently elevated ASO titers:

1. Determine if the patient is a GAS carrier:

   • Carriers have GAS present in the pharynx but show no evidence of active immunologic response 1
   • Up to 20% of asymptomatic school-age children may be GAS carriers during winter/spring 1

2. Rule out active infection:

   • Perform throat culture and/or rapid antigen detection test (RADT) 1
   • Consider testing for anti-DNase B if ASO is positive but clinical picture is unclear 2

3. Assess for symptoms of recurrent pharyngitis:

   • Differentiate between true recurrent GAS infections and viral infections in a GAS carrier 1

Treatment Algorithm

1. Asymptomatic Patients with Elevated ASO Titers

• No treatment is recommended 1
• Monitor for development of symptoms
• Reassure that carriers are at minimal risk for complications 1

2. Symptomatic Patients with Recurrent Pharyngitis and Positive Cultures

Consider one of the following treatment regimens for chronic carriers 1:

• First-line: Oral clindamycin 20-30 mg/kg/day in 3 doses (max 300 mg/dose) for 10 days
• Alternative: Penicillin V 50 mg/kg/day in 4 doses for 10 days plus rifampin 20 mg/kg/day for last 4 days
• Alternative: Amoxicillin-clavulanic acid 40 mg amoxicillin/kg/day in 3 doses for 10 days
• Alternative: Benzathine penicillin G (600,000 U for <27 kg, 1,200,000 U for ≥27 kg) plus rifampin 20 mg/kg/day in 2 doses for 4 days

3. Special Situations Warranting Treatment of GAS Carriers 1

Treatment is indicated only in these specific circumstances:

• Community outbreak of acute rheumatic fever, post-streptococcal glomerulonephritis, or invasive GAS infection
• Outbreak of GAS pharyngitis in a closed community
• Family or personal history of acute rheumatic fever
• Family with excessive anxiety about GAS infections
• When tonsillectomy is being considered solely due to carriage

Monitoring and Follow-up

• Routine post-therapy testing is not recommended for patients with acute GAS pharyngitis 1
• Follow-up is only needed for those with recurrent symptoms 1
• Tonsillectomy is not recommended solely to reduce frequency of GAS pharyngitis 1

Common Pitfalls to Avoid

1. Overtreatment: Treating elevated ASO titers without clinical symptoms or positive cultures
2. Misinterpretation: Assuming elevated titers indicate active infection rather than past infection 2
3. Inappropriate testing: Relying solely on ASO without considering clinical context 2
4. Unnecessary tonsillectomy: Evidence shows that tonsillectomy based solely on elevated ASO titers without confirmed GABHS in the tonsils is not justified 3

Remember that ASO titers can remain elevated for months after an infection, and treating based on titers alone without clinical correlation can lead to unnecessary antibiotic use.