Diphtheria

Basics

Description

Acute infectious disease caused by Corynebacterium diphtheriae; affects primarily the membranes of the upper respiratory tract with the formation of a gray-white pseudomembrane

Epidemiology

The only known reservoir for C. diphtheriae is humans; disease is acquired by contact with either a carrier or a diseased person.
Most cases occur during the cooler autumn and winter months in individuals <15 years of age who are unimmunized.
Recent outbreaks have occurred, most notably in the countries of the former Soviet Union, and supply additional evidence that disease occurs among the socioeconomically disadvantaged living in crowded conditions.

Incidence

Although the disease is distributed throughout the world, it is endemic primarily in developing regions of Africa, Asia, and South America.
In the Western world, the incidence of diphtheria has changed dramatically in the past 50 to 75 years as a result of the widespread use of diphtheria toxoid after World War II.
The incidence has declined steadily and is now a rare occurrence.

General Prevention

Active immunization with diphtheria toxoid is the cornerstone of population-based diphtheria prevention. Current recommendations from the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) are as follows:

Ages 2 months to 7 years: 5 doses of diphtheria vaccine (with tetanus toxoid and acellular pertussis)
- First three given as DTaP vaccine 0.5 mL IM at 2-month intervals beginning at 2 months of age
- Fourth dose of DTaP should be given at 15 to 18 months of age.
- Fifth dose of DTaP at 4 to 6 years of age
In 2005, 2 tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccines were licensed for use in adolescents 11 to 18 years of age.
1 booster dose of Tdap should be given to all adolescents at the 11- to 12-year-old visit, provided they have completed the childhood series. Subsequent tetanus and diphtheria (Td) boosters should be administered every 10 years.
Tdap should replace the first dose of Td in children 7 to 10 years of age who are undergoing primary immunization.
Isolation of patients with diphtheria is required until culture from the site of infection is negative on two consecutive specimens.

Pathophysiology

The initial entry site for C. diphtheriae is via airborne respiratory droplets, typically the nose or mouth but occasionally the ocular surface, genital mucous membranes, or preexisting skin lesions.
Following 2 to 4 days of incubation at one of these sites, the bacterium elaborates toxin.
Locally, the toxin induces formation of a necrotic coagulation of the mucous membranes (pseudomembrane) with underlying tissue edema; respiratory compromise may ensue.
Elaborated exotoxin may also have profound effects on the heart, nerves, and kidneys in the form of myocarditis, demyelination, and tubular necrosis, respectively.

Etiology

C. diphtheriae, a gram-positive pleomorphic bacillus

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