Diphtheria: A Clinical Overview

Based on CDC's clinical overview for health care providers.

Diphtheria is an acute disease caused by toxin-producing strains of Corynebacterium diphtheriae, an aerobic gram-positive bacillus. It is very rare in the United States and is usually linked to international travel to an area where it is endemic. Because it can cause severe illness and death, prompt diagnosis and treatment matter.

Toxigenic and nontoxigenic strains

A C. diphtheriae strain is toxigenic, able to produce diphtheria toxin, when two things are true:

1. It carries the diphtheria tox gene, because it has been infected (lysogenized) by a bacteriophage, a virus that infects bacteria, that carries the gene, or it descends from a strain that was.
2. It expresses the gene, actually making the toxin.

Most C. diphtheriae in the United States lack the tox gene, and in recent years the U.S. strains that carried it have not produced toxin. Toxigenic C. diphtheriae is not endemic in the country.

Illness from nontoxigenic strains, which lack the gene or do not express it, is not called diphtheria. It is less likely to be severe: usually a mild sore throat, rarely a membranous pharyngitis, though invasive disease such as bacteremia and endocarditis has been reported. Diphtheria antitoxin does not help against these infections, since the strains make no toxin.

Who is at risk

• Travelers. Diphtheria is extremely unlikely in a patient who has not traveled internationally; without travel, consider testing for other pathogens.
• Close contacts of a patient: everyone in the household, people with habitual close contact, and anyone directly exposed to secretions from the infection site.

Spread and incubation

• Most often, person to person through respiratory droplets.
• Also through direct contact with infected sores or ulcers, especially among people in frequent close contact.
• Rarely, through objects soiled by discharge from skin lesions.

The incubation period is usually 2–5 days (range 1–10). Diphtheria's clinical features can be confused with those of other infections.

Prevention

• Prophylaxis is recommended for close contacts of diphtheria patients, whatever their vaccination status.
• Vaccination is recommended for people of all ages; following CDC's immunization schedule keeps patients protected.

Diphtheria is a reportable condition in the United States.

Sources

• CDC, "Clinical Overview of Diphtheria": https://www.cdc.gov/diphtheria/hcp/clinical-overview/index.html
• CDC, clinical features, clinical guidance and vaccine recommendations for diphtheria: https://www.cdc.gov/diphtheria/hcp/clinical-signs/index.html, https://www.cdc.gov/diphtheria/hcp/clinical-guidance/index.html, https://www.cdc.gov/diphtheria/hcp/vaccine-recommendations/index.html