Diphtheria

Definition and transmission

Diphtheria is infection with Corynebacterium diphtheriae. Respiratory spread occurs through droplets from symptomatic or asymptomatic carriers; transmission can also occur through contaminated objects or contact with diphtheria skin lesions.

The incubation period is usually 1 to 5 days and can extend to 10 days. Toxin production causes local membrane formation and systemic injury.

Untreated cases can remain infectious for weeks. Antibiotics shorten infectiousness, but clinical management must begin on suspicion and should not wait for laboratory confirmation.

Clinical features

• Use standard, contact, and droplet precautions during examination: hand hygiene, gloves, gown, and mask according to local IPC policy.
• Respiratory diphtheria can present as pharyngitis, rhinopharyngitis, tonsillitis, or laryngitis with tough grey adherent pseudomembranes on the pharynx, nasopharynx, tonsils, or larynx.
• Dysphagia and tender cervical adenitis may progress to marked neck swelling. Fever is often low-grade despite severe disease.
• Extension to the nose, larynx, trachea, or bronchi can cause airway obstruction and suffocation.
• Toxin effects can cause tachycardia, arrhythmia, myocarditis, heart failure, cardiogenic shock, neuropathies, respiratory muscle paralysis, oliguria, anuria, and acute renal failure.
• Neurological complications may appear 2 to 8 weeks after onset; myocarditis can appear within the first week or later at 2 to 3 weeks.
• Important differentials include epiglottitis, acute pharyngitis, stomatitis, and other causes of oral or throat membrane.

Laboratory investigation and notification

• Confirm diagnosis where possible by culture of swabs from affected areas such as tonsils, pharyngeal mucosa, soft palate, exudate, ulcer, or nasopharynx; request antibiotic susceptibility testing when available.
• PCR testing can confirm presence of the diphtheria toxin gene.
• Collect swabs before antibiotics when this will not delay treatment. Do not delay antitoxin or antibiotics when clinical suspicion is high.
• A suspected case is pharyngitis, rhinopharyngitis, tonsillitis, or laryngitis with adherent pseudomembrane of the pharynx, nose, tonsils, or larynx.
• Notify public-health authorities within 24 hours or according to local outbreak rules.

Immediate management and antitoxin

Isolate the patient and use standard, droplet, and contact precautions. Assess airway, breathing, circulation, hydration, myocarditis signs, neurological signs, and swallowing safety.

Diphtheria antitoxin neutralises circulating toxin and should be given as soon as possible after onset when indicated. Do not wait for bacteriological confirmation.

Because antitoxin is horse-serum derived, administer only where close monitoring and resuscitation are available. Manual ventilation equipment, intubation capability or referral, Ringer lactate, and epinephrine must be ready.

• For IV antitoxin doses over 20 000 units, dilute in 250 ml 0.9% sodium chloride and infuse over 2 to 4 hours according to protocol.
• Intubation or tracheotomy may be needed for airway obstruction or respiratory failure. Avoid unnecessary manipulation of the membrane.
• If shock occurs, use the shock pathway while continuing diphtheria-specific management.

Antibiotic treatment

Start antibiotics as soon as diphtheria is suspected, without waiting for laboratory confirmation. Treat for 14 days or for the duration specified by national protocol.

• Change to oral treatment as soon as swallowing is safe to complete the full course.
• Update vaccination status before discharge or during the first visit if home-based care is used. If antitoxin was given and reliable follow-up is possible, defer vaccination for 3 weeks after antitoxin.

Close contacts and outbreak control

• Close contacts include household members and people directly exposed within one metre to nasopharyngeal secretions on a regular basis during the 5 days or nights before symptom onset.
• Collect nasal and pharyngeal swabs for culture before prophylaxis where feasible. Monitor temperature and throat examination daily for 10 days.
• Exclude close contacts from school or work until 48 hours after starting antibiotic prophylaxis. If respiratory symptoms develop, treat immediately as diphtheria.
• Prophylaxis options include benzathine benzylpenicillin IM once, azithromycin PO for 7 days, or erythromycin PO for 7 days according to local protocol.

Prevention, complications, and handover

• Routine vaccination is central to prevention. Infant schedules use diphtheria-containing vaccine from 6 weeks of age according to local EPI, with later boosters. Catch-up schedules are needed for under-vaccinated children, adolescents, adults, and medical staff.
• Clinical diphtheria does not reliably protect against future disease; vaccination remains part of case management.
• Complications include airway obstruction, suffocation, myocarditis, arrhythmias, heart failure, cardiogenic shock, neuropathy, respiratory muscle paralysis, renal failure, and death.
• Handover should include onset date, vaccination history, membrane site, airway findings, neck swelling, cardiac rhythm or myocarditis signs, neurological signs, urine output, specimens collected, antitoxin dose/time/reaction, antibiotics, contact list, IPC measures, and notification status.