Diphtheria

Acute infection by toxin-producing Corynebacterium diphtheriae affecting the respiratory tract (or skin). It causes a tough pseudomembrane on mucous membranes and can lead to life-threatening systemic toxin effects (notably myocarditis and neuropathy).

• Often fatal if untreated (up to ~30% in unvaccinated). Historically a major childhood killer before vaccines, it is now rare but outbreaks occur with low immunization coverage. Rapid recognition and antitoxin treatment are critical, making diphtheria a classic exam topic in infectious disease and public health.

• Classic respiratory diphtheria – Unimmunized patient with a gradually worsening sore throat, low-grade fever, and a gray, adherent pseudomembrane on the tonsils/pharynx. Neck swelling (bull neck) from cervical lymphadenopathy and edema is seen in severe cases, and airway obstruction (stridor) can occur.
• Cutaneous diphtheria – Infection of the skin at a wound or ulcer, causing a chronic, non-healing ulcer with a dirty gray membrane. Typically seen in unhygienic or immunocompromised settings; usually localized with mild systemic symptoms.
• Systemic complications – After a few days to weeks, the diphtheria exotoxin can disseminate and damage distant organs. Look for myocarditis (arrhythmias, heart failure) and peripheral neuropathy (e.g. palatal paralysis, cranial nerve palsies) in severe cases.

1. If diphtheria is suspected, do not wait for lab confirmation – begin antitoxin therapy right away.
2. Obtain swabs from the throat (or wound) before starting antibiotics for culture on special media (e.g., cystine-tellurite agar shows characteristic black colonies of *C. diphtheriae*).
3. Confirm toxigenicity of the isolate with the Elek test (in vitro toxin assay) or PCR for the toxin gene.
4. A firmly attached gray membrane in the throat that bleeds when scraped is a diagnostic clue pointing to diphtheria.

1. Diphtheria antitoxin (horse serum) – administer immediately if diphtheria is suspected (neutralizes circulating toxin; perform a test dose to check for hypersensitivity).
2. Antibiotics – give erythromycin (preferred) or intramuscular penicillin G for ~14 days to eradicate *C. diphtheriae* (also give antibiotic prophylaxis to close contacts).
3. Isolation & notification – isolate the patient under droplet precautions until 2 consecutive cultures (after antibiotics) are negative; notify public health authorities to facilitate contact tracing and quarantine.
4. Supportive care – secure the airway (pseudomembranes may require careful endoscopic removal if causing obstruction) and monitor in ICU for cardiac arrhythmias or respiratory failure. After recovery, ensure the patient is vaccinated (infection does not confer reliable immunity).

• Gray pseudomembrane firmly adherent to the throat and bleeding if scraped = hallmark of diphtheria (unlike thrush, which is easily removable).
• Bull neck describes the massive neck swelling in severe diphtheria due to lymphadenopathy and edema.
• Mnemonic ABCDEFG for diphtheria toxin – ADP-ribosylation (of EF-2) by Beta-prophage gene in Corynebacterium Diphtheriae leads to Elongation Factor-2 inhibition and Granules (blue-red metachromatic granules on Löffler medium).

• Extensive bull neck swelling with stridor or respiratory distress – indicates impending airway obstruction (emergency intervention needed).
• Evidence of toxin spread: new-onset arrhythmias, heart block or heart failure (myocarditis), or cranial nerve palsies and paralysis (neuritis) – signal severe diphtheria (high mortality, ICU care needed).

1. Unvaccinated person with sore throat + pseudomembrane → suspect diphtheria (clinical diagnosis).
2. If suspected, administer antitoxin immediately – do not wait for lab results.
3. Secure airway as needed; obtain throat (or lesion) swabs for culture and toxin testing (Elek test or PCR).
4. Start antibiotics (erythromycin or penicillin) and maintain droplet isolation precautions.
5. Report the case to public health; give close contacts prophylactic antibiotics and booster vaccine; once recovered, update the patient's diphtheria immunizations.

• Unvaccinated child with fever, sore throat, a gray leathery membrane on the tonsils, and neck swelling (bull neck) → Diphtheria (respiratory infection).
• Patient recovering from a severe throat infection now develops arrhythmia and heart failure → myocarditis from diphtheria toxin.
• Homeless patient with a chronic non-healing leg ulcer covered by a gray membrane but minimal systemic illness → cutaneous diphtheria.