What is the recommended treatment for contacts of a diphtheria patient?

Treatment for Diphtheria Contacts

All close contacts of diphtheria patients should receive prompt antimicrobial prophylaxis, throat cultures, daily monitoring for 7 days, and vaccination updates regardless of their vaccination status. 1, 2

Antimicrobial Prophylaxis

Antimicrobial prophylaxis should be initiated immediately without waiting for culture results and consists of either:

• Benzathine penicillin (single IM injection):
  • Children <6 years: 600,000 units
  • Persons ≥6 years: 1,200,000 units

OR

• Erythromycin (oral for 7-10 days):
  • Children: 40 mg/kg/day
  • Adults: 1 g/day

While erythromycin may be slightly more effective, benzathine penicillin is often preferred due to guaranteed compliance with a single-dose regimen 1. However, erythromycin resistance has been documented in some regions 3, which may influence the choice of antimicrobial agent.

Vaccination Updates

All contacts require vaccination assessment:

• Contacts with <3 doses of diphtheria toxoid or unknown status:

  • Immediate dose of diphtheria toxoid-containing vaccine
  • Complete primary series according to schedule

• Contacts with ≥3 doses but no booster in past 5 years:

  • Administer age-appropriate booster dose of diphtheria toxoid-containing vaccine 1, 2

Monitoring and Follow-up

• Obtain throat cultures from all close contacts before starting antimicrobial prophylaxis
• Monitor contacts daily for 7 days for signs of disease
• Perform follow-up cultures after completion of antimicrobial therapy
• For persistent carriers after initial treatment:
  • Administer additional 10-day course of oral erythromycin
  • Conduct further follow-up cultures 1

Passive Immunization

Equine diphtheria antitoxin is generally not recommended for contacts due to:

• Risk of allergic reactions (7% immediate hypersensitivity, 5% serum sickness)
• No proven additional benefit for contacts receiving antimicrobial prophylaxis

If antitoxin is considered necessary in exceptional circumstances:

• Administer 5,000-10,000 units IM after sensitivity testing
• Inject at a different site from toxoid if given concurrently 1

Special Considerations

For cutaneous diphtheria:

• If toxigenic strain: manage contacts as for respiratory diphtheria
• If non-toxigenic strain: routine investigation or prophylaxis of contacts is not necessary 1

Common Pitfalls

1. Delayed prophylaxis: Never wait for culture results before initiating antimicrobial prophylaxis
2. Incomplete contact tracing: Ensure all household members and close contacts are identified
3. Inadequate follow-up: Failure to perform post-treatment cultures may miss persistent carriers
4. Overlooking vaccination status: Always update vaccination status regardless of antimicrobial prophylaxis

The efficacy of antimicrobial prophylaxis in preventing secondary disease is presumed but not definitively proven 1. Nevertheless, prompt implementation of these measures is critical to prevent the spread of this potentially fatal disease.