Diphtheria

Diphtheria is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Acute respiratory tract infection typically presenting as a membranous pharyngitis, caused by the gram-positive facultative anaerobic bacterium Corynebacterium diphtheriae
  • Greek name “diphtheria,” translated as “leather hide”
  • Incubation period 2 to 5 days (range 1 to 10 days)
  • Infection peaks in fall and winter in temperate regions:
    • Seasonal trends are less distinct in the tropics.
    • Cutaneous form peaks in August to October in Southern United States.
  • Transmission by respiratory spread from infected person or carrier
    • Humans are the only reservoir.
    • Rarely transmitted directly from skin lesions or contaminated fomites
  • Several forms occur:
    • Membranous pharyngotonsillar diphtheria
    • Nasal diphtheria
    • Obstructive laryngotracheitis
    • Cutaneous diphtheria
  • System(s) affected: cardiovascular, nervous, skin/exocrine, respiratory, renal

Epidemiology

  • Predominant age: children <15 years and poorly immunized adults
  • Predominant sex: male = female

Incidence
  • United States: noncutaneous form, 1.6 in 100 million
    • Diphtheria rare in the United States
  • Worldwide in 2017: 8,819 cases reported to the World Health Organization (WHO)
  • Recent outbreaks have occurred in Brazil, West Africa, Ukraine, Poland, India, New Zealand, and the tropical Polynesian Islands.

Etiology and Pathophysiology

Toxigenic strains of C. diphtheriae produce an exotoxin that inhibits protein synthesis in all cell types. Toxin causes local damage and necrosis of the pharyngeal membranes. Toxin is absorbed and disseminated hematogenously and can lead to myocarditis and neuritis.

Risk Factors

  • Crowded living conditions
  • Inadequate immunization
  • Lower socioeconomic status
  • Native American ethnicity
  • Alcoholism
  • Travelers: outbreaks reported in various countries

General Prevention

Immunization: diphtheria toxoid (inactivated toxin)

  • Primary series of five immunizations. Children should receive doses at 2, 4, 6, 15 to 18 months and 4 to 6 years of age with 0.5 mL of DTaP vaccine IM. A booster dose of adult Tdap should be given at 11 to 12 years. If the pertussis component is contraindicated, then pediatric diphtheria tetanus (DT) should be used.
  • Due to the rise in pertussis, new Advisory Committee on Immunization Practices recommendations include a Tdap dose during each pregnancy (regardless of prior immunizations), ideally given between 27 and 36 weeks’ gestation.
  • Unimmunized persons ≥7 years should receive 2 doses of adult Td 4 to 8 weeks apart, with a third dose 6 to 12 months later. 0.5 mL of Td should be given. Subsequently, booster doses with Td should be given every 10 years to all individuals without a contraindication.
  • CDC recommends substituting Tdap for one of the decennial Td boosters.
  • Immunized individuals may develop a milder course of diphtheria; immunization protects against the toxin (not infection or microbial carriage).
  • Culture close contacts and give antibiotic prophylaxis, regardless of immunization status.
  • Contacts should receive a diphtheria toxoid-containing vaccine unless vaccinated within the past 5 years.

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