Classic diphtheria is characterized by the formation of a pseudomembrane on respiratory mucous membranes. Initial testing includes CBC and a rapid strep test. A diphtheria culture is usually diagnostic if disease symptoms are present.
Tabs Content Clinical Overview Diagnosis
Indications for Testing
Presence of pseudomembrane
Pharyngitis with other organ involvement
Laboratory Testing
Differential Diagnosis
Pharyngitis
Skin lesions
Cough
Pneumonia
Asthma
Bronchiolitis
Background
Epidemiology
Incidence – very rare in U.S. due to vaccination
Age – usually in children <15 years who are unvaccinated or incompletely vaccinated
Transmission – airborne or direct contact (respiratory secretions or skin lesion)
Organism
Gram-positive bacillus
Not spore forming
Unencapsulated
Pleomorphic
Produces exotoxin that causes many of the symptoms
Results in asymptomatic carriage in some patients
Pathophysiology
Virulence is mediated by prophage-encoded exotoxin
Toxin induces dense necrotic coagulum on mucous membranes
Causes underlying soft-tissue edema
Clinical Presentation
Incubation period – 2-4 days
Respiratory tract involvement
Anterior nasal disease
Faucial disease – classic membranes on pharynx and tonsils, cervical adenopathy, and fever
Laryngeal and tracheobronchial disease – hoarseness, dyspnea, stridor, and brassy cough
Cardiac disease – myocarditis
Mortality 3-4 times that of patients without cardiac involvement
Related to toxin release
Neurologic disease – demyelinating neuropathy
Usually motor neuropathy
Related to severity of disease – rare in mild disease
Renal disease – proteinuria, renal failure
Cutaneous disease – chronic nonhealing ulcers with dirty gray membrane, often in mixed infections with Staphylococcus aureus and group A streptococci
Invasive disease
Prevention
Vaccination
ARUP Lab Tests
Identify Corynebacterium diphtheriae in clinical specimens
Identify infectious process
Rule out more common cause of pharyngitis
If Streptococcus (Group A) rapid test is negative and patient is ≤18 years, culture will be added for confirmation
Evaluate the ability of a patient to produce antibody to pure protein vaccines after vaccination to rule out antibody deficiency
Evaluate the ability of a patient to produce antibody to pure protein vaccine after vaccination to rule out antibody deficiency
Evaluate the ability of a patient to produce antibody to pure protein vaccines (diphtheria and tetanus) and protein conjugated bacterial (Haemophilus influenza ) vaccines after vaccination to rule out antibody deficiency
References Resources from the ARUP Institute for Clinical and Experimental Pathology®
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Last Update: October 2019