Diphtheria is an acute, bacterial disease caused by toxin-producing strains of Corynebacterium diphtheriae. Infection can result in respiratory or cutaneous disease. Two other Corynebacterium species (C. ulcerans and C. pseudotuberculosis) may produce diphtheria toxin; both species are zoonotic. Toxin-producing C. ulcerans may cause classic respiratory diphtheria-like illness in humans, but person-to-person spread has not been documented.
Non-toxin-producing strains of C. diphtheriae can also cause disease. It is generally less severe, potentially causing a mild sore throat and, rarely, a membranous pharyngitis. Invasive disease, including bacteremia and endocarditis, has been reported for non-toxin-producing strains of C. diphtheriae.
Vaccination is highly protective against disease caused by toxin-producing strains, but does not prevent carriage of C. diphtheriae, regardless of toxin production status.
C. diphtheriae is an aerobic gram-positive bacillus. Toxin production (toxigenicity) occurs only when the bacillus is itself infected (lysogenized) by a specific virus (bacteriophage) carrying the genetic information for the toxin (tox gene).
Transmission is most often person-to-person spread from the respiratory tract. Rarely, transmission may occur from skin lesions or articles soiled with discharges from lesions of infected persons (fomites).
The incubation period of diphtheria is usually 2–5 days (range: 1–10 days). Diphtheria can involve almost any mucous membrane. For clinical purposes, it is convenient to classify diphtheria into type of manifestation, depending on the site of disease:
- Respiratory diphtheria
- Nasal diphtheria
- Pharyngeal and tonsillar diphtheria
- Laryngeal diphtheria
- Cutaneous diphtheria
Respiratory diphtheria has a gradual onset and is characterized by:
- Mild fever
- Sore throat
- Difficulty swallowing
- Loss of appetite
- Hoarseness (if the larynx is involved)
The hallmark of respiratory diphtheria is a pseudomembrane that appears within 2–3 days of illness over the mucous lining of the tonsils, pharynx, larynx, or nares and that can extend into the trachea. Fatal airway obstruction can result if the pseudomembrane extends into the larynx or trachea or if a piece of it becomes dislodged.
Cutaneous diphtheria may present as a scaling rash or as ulcers with clearly demarcated edges and membrane, but any chronic skin lesion may harbor C. diphtheriae along with other organisms. The systemic complications from cutaneous diphtheria with toxigenic strains appear to be less than from other sites.
When C. diphtheriae is identified, it is critical that state and local public health laboratories submit specimens or isolates to CDC for confirmatory testing so that appropriate public health action can be taken. CDC’s Pertussis and Diphtheria Laboratory is currently the only laboratory in the United States that performs the Elek test.
Diagnosis of diphtheria is confirmed by isolating C. diphtheriae and testing the isolate for toxin production by the Elek test, an in vitro immunoprecipitation (immunodiffusion) assay. Other tests, such as polymerase chain reaction (PCR) and matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF), may identify C. diphtheriae. However, when used alone, these tests do not confirm toxin production and are considered supplemental.
Specimens for culture should be obtained from the nares and oropharynx, or any mucosal or cutaneous lesion. If possible, material should be obtained from beneath the membrane (if present) or a portion of the membrane itself. Specimens are more likely to be culture-positive if obtained before the patient receives antibiotic treatment.
Respiratory diphtheria is uncommon in the United States. Infection with other pathogens could result in a similar clinical presentation as diphtheria; testing for other pathogens should be considered. Pathogens include group A beta-hemolytic Streptococcus, Staphylococcus aureus, Candida albicans, and viruses such as Epstein-Barr, cytomegalovirus, adenovirus, and herpes.
Diagnosis of respiratory diphtheria is usually made on the basis of clinical presentation since it is imperative to begin presumptive therapy quickly. After making the provisional clinical diagnosis, obtain appropriate clinical specimens, and start antitoxin and antibiotic treatment. Respiratory support and airway maintenance may be needed.
Even though disease is usually not contagious 48 hours after antibiotic treatment begins, maintain droplet precautions until the diphtheria patient has completed the antibiotic course and is culture-negative. Document elimination of the organism by obtaining two consecutive negative cultures 24 hours apart, once antibiotic therapy is completed.
Treatment of cutaneous diphtheria with antibiotics is usually sufficient, and antitoxin is typically not needed.
Diphtheria disease might not confer immunity. Persons recovering from diphtheria should begin or complete active immunization with diphtheria toxoid during convalescence if not fully up to date with vaccination.
In the United States, clinicians can obtain diphtheria antitoxin from CDC on request. Learn more about diphtheria antitoxin and how to request it.
The recommended antibiotics for respiratory or cutaneous diphtheria is either erythromycin or penicillin.
Most complications of respiratory diphtheria, including death, are attributable to effects of the toxin. The most frequent complications of respiratory diphtheria are myocarditis and neuritis. Other complications include otitis media and respiratory insufficiency due to airway obstruction, especially in infants.
The overall case-fatality rate for diphtheria is 5%–10%, with higher death rates (up to 20%) among persons younger than 5 and older than 40 years of age.
Cutaneous diphtheria infection rarely results in severe disease.
State or local health departments conduct a contact investigation for all suspected respiratory and non-respiratory diphtheria cases. This investigation should include:
- Obtaining nasal and throat cultures
- Collecting preliminary epidemiologic and clinical information
- Identifying close contacts
Close contacts of diphtheria patients include:
- All household members
- Persons with a history of habitual, close contact with the patient
- Persons directly exposed to secretions from the suspected infection site of the patient
Management of close contacts should include monitoring for possible respiratory or cutaneous diphtheria for 7 to 10 days from the time of the last exposure to the diphtheria patient and obtaining nasal and throat cultures for C. diphtheriae. Close contacts should also receive erythromycin . For compliance reasons, if the health department cannot maintain surveillance of close contacts, the close contacts should receive benzathine penicillin. The health department should also direct close contacts to receive a diphtheria toxoid booster, appropriate for age, if they are not up to date with diphtheria vaccination.
Close contacts of cutaneous diphtheria should be treated as described above; however, if the strain is shown to be nontoxigenic, the health department can discontinue investigation of contacts.
The National Notifiable Diseases Surveillance System conducts national surveillance for diphtheria. CDC also identifies cases by requests for diphtheria antitoxin (DAT); since 1997, DAT is available for U.S. healthcare professionals only through CDC.