Diphtheria

Diphtheria is a vaccine-preventable, toxin-mediated bacterial disease caused by Corynebacterium diphtheriae.

Outbreaks occur across the globe in populations with low vaccine coverage. Sporadic cases occur in settings where vaccine coverage is high, mainly focused among vulnerable individuals who have arrived from places of higher risk.

Respiratory diphtheria is the main clinical presentation. Local, toxin-mediated inflammation can cause life-threatening upper airway obstruction. Systemic dissemination of toxin can cause delayed mortality from cardiac and neurological damage.

Cutaneous diphtheria is another common presentation; it is usually less severe.

Early intervention by administering antitoxin is key to preventing severe manifestations of the disease. Prompt administration of antitoxin is necessary to deactivate free toxin in serum before it enters cells.

Antibiotic treatment is required to eliminate the bacteria and prevent further transmission. Protective immunity does not always develop after recovery, so toxoid vaccination of patients, contacts, and the general population is important for diphtheria prevention and control.

To minimise transmission, patients with respiratory diphtheria require respiratory and contact precautions (including isolation, facemasks, gloves, and gowns), and those with cutaneous diphtheria require contact isolation, ideally until cultures taken after completion of therapy are negative.

Most disease transmission is attributable to symptomatic cases, but asymptomatic carriers also play a role.

Respiratory diphtheria is an upper respiratory tract illness caused by exotoxin-producing strains of Corynebacterium diphtheriae. Rarely, it may also be caused by other corynebacteria that produce diphtheria toxin, such as Corynebacterium ulcerans or Corynebacterium pseudotuberculosis.[1]Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases. Chapter 1: diphtheria. Dec 2022 [internet publication]. https://www.cdc.gov/vaccines/pubs/surv-manual/chpt01-dip.html ​ It is characterised by sore throat, fever, and an adherent pseudomembrane that can cover the tonsils and mucosa of the pharynx, larynx, and nose. Occasionally, the mucosa of the eyes, ears, or genitals may also be affected. Enlarged anterior cervical lymph nodes and oedema of the surrounding soft tissue can cause a characteristic ‘bull-neck’ appearance. The toxin causes tissue necrosis and formation of the pseudomembrane. It also causes the major late complications of myocarditis and neuritis.

Cutaneous diphtheria may be caused by toxigenic or non-toxigenic strains of C diphtheriae and is usually a milder disease, causing cutaneous sores or shallow ulcers. Toxic complications are rare in cutaneous disease.​[2]Centers for Disease Control and Prevention. Diphtheria: clinical features of diphtheria​. Feb 2024 [internet publication]. https://www.cdc.gov/diphtheria/hcp/clinical-signs ​[3]Moore LSP, Leslie A, Meltzer M, et al. Corynebacterium ulcerans cutaneous diphtheria. Lancet Infect Dis. 2015 Sep;15(9):1100-07. http://www.ncbi.nlm.nih.gov/pubmed/26189434?tool=bestpractice.com