Diphtheria Primarily Infects the Upper Respiratory Tract
Diphtheria infection by Corynebacterium diphtheriae primarily affects the upper respiratory tract, specifically the tonsils, pharynx, and nose, where it forms a characteristic adherent gray pseudomembrane. 1, 2
Primary Sites of Infection
The bacterium predominantly colonizes and infects:
- Pharynx and tonsils - These are the most common sites of infection, presenting with sore throat as the hallmark initial symptom 2, 3
- Nasal cavities - The nose can be involved, with the pseudomembrane extending to nasal mucosa 1, 2
- Larynx - Laryngeal involvement is particularly dangerous and represents a dire prognostic sign 2, 4
- Soft palate and uvula - These structures can be affected as part of the upper respiratory tract involvement 5
Characteristic Pathology
The infection produces a distinctive gray-colored pseudomembrane that is firmly adherent to the mucosa of the affected respiratory structures 2. This pseudomembrane formation in the throat, combined with low-grade fever, defines the clinical presentation according to CDC case definitions 1.
Life-Threatening Extension
Extension of the pseudomembrane into the trachea-bronchial tree can cause fatal airway obstruction, making laryngeal membrane presence an indication for considering tracheotomy 2, 4. Dyspnea and laryngeal membrane are particularly ominous findings 4.
Less Common Sites
While respiratory diphtheria is the primary concern:
- Cutaneous diphtheria can occur at wound sites but is not reportable in the United States and is generally less severe 1
- Stomach or lungs are rarely affected sites 5
- Tongue and floor of mouth represent unusual presentations 6
Systemic Complications
Though the infection is localized to respiratory mucosa, systemic absorption of diphtheria toxin causes distant organ damage, including myocarditis and neuropathy, which are the major causes of mortality beyond airway obstruction 2, 7.
Clinical Pitfall
The key diagnostic error is failing to perform indirect laryngoscopy in all cases showing membrane formation, as laryngeal involvement dramatically increases mortality risk and may require urgent airway intervention 4.