Diphtheria is caused by toxin-producing bacteria, Corynebacterium diphtheriae, and less frequently by one of two other, zoonotic, Corynebacteria.
Diphtheria toxin destroys tissue, which builds up in the throat and tonsils, making breathing and swallowing almost impossible.
The bacteria are transmitted by respiratory droplets, by direct physical contact with skin lesions, via secretions from infected patients, or contaminated materials.
Clinically, tonsillitis, pharyngitis, laryngitis, and skin infections (wound infection; ulcers) appear; diphtheria once was a terrible killer of young children.
Antibiotics (penicillin, erythromycin, others) are used to eradicate the bacteria; for respiratory infections, diphtheria antitoxin is used to neutralize circulating toxins and reduce/prevent complications like myocarditis, neuritis (nerve palsies).
Case fatality rates of up to 10% have been reported during diphtheria outbreaks, and are even higher in settings where diphtheria antitoxin is unavailable.
Diphtheria vaccines consist of inactivated toxins, called toxoids, and are available in combinations with other antigens such as tetanus, pertussis, and others.
These combinations are usually well-tolerated, local reactions are the most frequently observed side effects.
Efficacy studies are not available but various observational studies consistently indicate high vaccine effectiveness between 87% and 96%.