What are the steps for diagnosing and treating diphtheria?

Diagnosis and Treatment of Diphtheria

Prompt diagnosis and immediate treatment with diphtheria antitoxin and appropriate antimicrobial therapy are essential for managing diphtheria and preventing potentially fatal complications. 1

Diagnostic Approach

Clinical Diagnosis

• Look for characteristic clinical presentation:
  • Upper respiratory tract illness with sore throat and low-grade fever
  • Adherent grayish membrane on the tonsils, pharynx, and/or nose 2
  • Respiratory symptoms that may include dyspnea (breathing difficulty)
  • Possible presence of bull neck (neck swelling) in severe cases
  • Possible cutaneous manifestations in cutaneous diphtheria

Laboratory Confirmation

1. Specimen collection: Obtain throat swabs or membrane samples before starting antibiotics if possible
2. Culture: Isolation of Corynebacterium diphtheriae from clinical specimen 2
3. Toxigenicity testing: Determine if the strain produces toxin
4. Serology: A serum specimen collected before antitoxin administration may help support diagnosis if diphtheria antitoxin level is below protective level (<0.01 IU/mL) 2

Treatment Protocol

Immediate Actions

1. Administer diphtheria antitoxin (DAT) immediately upon clinical suspicion without waiting for laboratory confirmation

   • DAT only neutralizes circulating toxin and cannot reverse damage from toxin already bound to tissues 1
   • Before administration, perform sensitivity testing due to risk of allergic reactions
   • Note: Immediate hypersensitivity reactions occur in approximately 7% and serum sickness in 5% of adults receiving equine antitoxin 2

2. Initiate antimicrobial therapy concurrently with DAT:

   • Erythromycin: 40 mg/kg/day for children; 1 g/day for adults for 7-10 days (may be slightly more effective) 2, 1
   • OR Benzathine penicillin: Single IM injection of 600,000 units for children <6 years old; 1,200,000 units for those ≥6 years old (preferred for guaranteed compliance) 2, 1

Supportive Care

• Monitor for complications, particularly:
  • Airway compromise (may require intubation or tracheostomy)
  • Myocarditis (leading cause of death) 3
  • Neurological complications
  • Renal failure

Follow-up

• Perform repeat cultures after completion of antimicrobial therapy
• If cultures remain positive, administer an additional 10-day course of oral erythromycin 2, 1

Management of Close Contacts

1. Identify close contacts: Household members and those directly exposed to oral secretions 2

2. For all close contacts regardless of vaccination status:

   • Obtain throat cultures
   • Provide antimicrobial prophylaxis (same regimens as treatment)
   • Monitor daily for 7 days for signs of disease 2, 1

3. Update vaccination status:

   • For contacts with <3 doses or unknown status: Immediate dose plus completion of primary series
   • For contacts with ≥3 doses but no booster in past 5 years: Administer booster dose 2, 1

Special Considerations

Cutaneous Diphtheria

• If toxigenic C. diphtheriae strain is isolated from a cutaneous lesion, manage contacts as with respiratory diphtheria
• If non-toxigenic strain is confirmed, routine investigation or prophylaxis of contacts is not necessary 2

Vaccination

• Active immunization with tetanus-diphtheria toxoid (Td) provides protection
• A serum diphtheria antitoxin level of 0.01 IU/mL is considered the minimum protective level 4

Pitfalls to Avoid

1. Delayed antitoxin administration: DAT should be given immediately upon clinical suspicion, as delay increases mortality risk 5
2. Inadequate airway management: Consider indirect laryngoscopy in all cases with membrane formation; tracheostomy may be needed with laryngeal membrane 6
3. Missing myocarditis: Development of myocarditis is an independent predictor of death 3
4. Inadequate contact tracing: Failure to identify and prophylactically treat close contacts can lead to secondary cases

Remember that diphtheria remains a potentially fatal infection with significant systemic effects due to the exotoxin produced by the pathogen 7. Early recognition and aggressive management are critical for favorable outcomes.