An acute bacterial toxigenic infectious disease caused by gram-positive bacillus, Corynebacterium diphtheriae.
Epidemiology
- Source: Secretions and discharges (infected person or carriers)
- Transmission: Droplet, secretions, direct contact
- Infection is spread solely among humans
- Portal of entry: Respiratory tract
- Incubation period: 2-5 days



Microbiology
Corynebacterium diphtheriae
Nonmotile, noncapsulated, club-shaped, Gram-positive bacillus
- Pathogenicity due to:
- Ability to colonise nasopharyngeal cavity and/or skin
- Diphtheria toxin

Macleod classification:
McLeod and Anderson classified diphtheria bacilli, based on the colony characteristics on Tellurite medium and other properties like biochemical reactions and severity of disease.
C. diphtheriae biotype | Colony appearance | Hemolysis | Glycogen & starch fermentation |
Gravis | Daisy head | Variable | Fermenting |
Intermedius | Frog egg | Non-hemolytic | Non-fermenting |
Mitis | Poached egg | Hemolytic | Non-fermenting |
Pathophysiology

Enter respiratory tract
↓
Proliferate and liberate powerful exotoxin
(Principal cause of systemic and local lesions)
↓
Necrosis of the epithelial cells
+
Liberation of serous and fibrinous material
↓
Forms a thick, gray-green fibrin membrane
Pseudomembrane
(composed of fibrin, bacteria, and inflammatory cells)
- Surrounding tissue: Inflamed and edematous
- Organs principally affected: Heart, kidney and myocardium
Presentation
Acute onset
- Fever, malaise and headache
- Toxic look
Clinical types (depends on the site of involvement):
- Respiratory diphtheria (M/C):
- Faucial/tonsillopharyngeal diphtheria
- Nasopharyngeal diphtheria
- Laryngotracheal diphtheria
- Cutaneous diphtheria
Faucial/tonsillopharyngeal diphtheria:
M/C respiratory diphtheria
- Redness and swelling over the fauces
- Pseudomembrane
- The exudates coalesce to form a greyish white pseudomembrane, which extends to surrounding areas.
- Localised on posterior pharynx or tonsil
- Wipes off easily, resulting in bleeding
- Extends to become thick blue-white to grey-black and adherent
- Bull neck diphtheria (severe cases, involvement of cervical lymph nodes)
- Sore throat, dysphagia and muffled voice


Nasal diphtheria (mildest respiratory diphtheria):
- Unilateral/bilateral serosanguinous discharge from the nose (localised to septum/turbinates)
- Excoriation of upper lip
Laryngotracheal diphtheria:
- Preceded by Pharyngotonsillar Disease
- Membrane over the larynx leads to: Brassy cough, stridor, respiratory distress
Cutaneous diphtheria:
- Diphtheritic lesions in skin and conjunctiva
- Secondary to previous skin lesion or infections
- Ulcer:
- Surrounded by erythema
- Covered by membrane

Complications
Respiratory failure (M/C)
- Due to occlusion of the airways by the membrane & loss of motor function (due to action of diphtheria toxin on peripheral motor neurons)
Myocarditis
- By 2nd week of illness
- Can lead to: Congestive cardiac failure, arrhythmias → Sudden death
Diphtheric mono/polyneuropathy (loss of motor function due to action of diphtheria toxin on peripheral motor neurons):
- Palatal palsy (by 2nd week of illness)
- Clinically manifested as: Nasal twang & nasal regurgitation
- Ocular palsy (by 3rd week of illness)
- Loss of accommodation (visual blurring, inability to read)
- Generalized polyneuritis (by 3rd-6th weeks of illness)

Renal complications:
- Oliguria
- Proteinuria
Diagnosis
High index of suspicion
- SGOT ↑
- CPK-MB ↑
- Troponin T (kit test)
- Urea, creatinine ↑
Rapid diagnosis:
- Culture: Albert stain
- Swab from the oropharynx and larynx
- Primary isolation media: Loeffler agar, Mueller-Miller tellurite agar,
or Tinsdale tellurite agar

Elek immunodiffusion test (M/C in vitro assay for toxigenicity):
- Based on the double diffusion of diphtheria toxin and antitoxin in an agar medium
- Procedure:
- Sterile, antitoxin-saturated filter paper strip is embedded in the culture medium, and C diphtheriae isolates are streak-inoculated at a 90° angle to the filter paper.
- Production of diphtheria toxin can be detected within 18-48 hours by the formation of a toxin-antitoxin precipitin band in the agar.

ECG (for cardiac complications):
- Findings:
- T-wave inversion
- Sinus tachycardia
- 2° AV block
Differential diagnosis:
- Acute streptococcal membranous tonsillitis
- High fever but are less toxic and the membrane is confined to the tonsils
- Viral (adenovirus) membranous tonsillitis
- High fever, sore throat, membranous tonsillitis with normal leukocyte count
- Self limited course of 4-8 days
- Herpetic tonsillitis
- Aphthous stomatitis
- Thrush
- Infectious mononucleosis
- Agranulocytosis
- Leukemia
Management
Goals of management:
- Early detection
- Isolation
- Treatment
Treatment for cases:
- Diphtheria antitoxin, IM/IV
- Dose: 20,000-100,000 units
- Degree of protection offered by the diphtheria antitoxin is inversely proportional to the duration of clinical illness
- Repeat doses may be given if clinical improvement is suboptimal.
- Penicillin or Erythromycin (5-6 days)
- Actions:
- Terminate toxin production
- Limit proliferation of bacteria
- Prevent spread of organism to contacts
- Prevent the development of carriers
- Actions:
Treatment for carriers:
- Oral Erythromycin
- 10-day course
Supportive therapy:
- Bed rest
- 2-3 weeks
- Avoid sudden exertion
- Monitored for:
- Airway obstruction and managed
- Tracheostomy (if required)
- Changes in rate and rhythm of heart
- Airway obstruction and managed
- Palatal palsy:
- Nasogastric feeding.
- Generalized weakness due to polyneuritis:
- Treated as for poliomyelitis or Guillain-Barre syndrome
Prevention:
Treatment should be followed by active immunization as clinical disease does not confer active immunity.