It is a global health problem. The disease occurs almost exclusively in persons who are unvaccinated, inadequately vaccinated, or whose history is unknown. In developing countries most reported illness occurs in infants and young children. Diphtheria is a bacterial infection that generally affects the upper respiratory sytstem and may be transmitted by coming into contact with infected persons or carriers. Diphtheria remains a serious disease throughout much of the world.
Most cases occur in unvaccinated or inadequately vaccinated persons.
In particular, large outbreaks of diphtheria have occurred throughout the New Independent States of the former Soviet Union. Pertussis primarily occurs in children and is common in countries where vaccination is not generally provided. It is highly communicable, often associated with complications, and has a relatively high case-fatality ratio in infants. Simultaneous vaccination against tetanus, diphtheria, and pertussis is generally provided for children less than 7 years of age. In children 7 years or older and in adults, simultaneous vaccination against tetanus and diphtheria is commonly used, without pertussis vaccine.