
Diphtheria is most common in areas where people live in crowded conditions with poor sanitation.
Race: Native Americans generally have much higher rates of diphtheria infection than whites.
Sex: studies suggest that women are at higher risk than men because of lower immunization rates.
Age: due to lack of routine immunization among the children aged 6-12 months the disease incidence increased drastically.

Known exposure, current epidemic, and travel to endemic areas increases risk

Compromised host, individuals addicted to alcohol and illicit drug users are at an increased risk of diphtheria.

Homosexual men have increased incidence rates.

Adults older than 60 years of age and who have not received immunization are at an increased risk of the disease.