Epiglottitis Causes. Conditions that cause epiglottitis include infectious, chemical, and traumatic agents. Infectious is the most common. H influenzae type b was once the most common cause prior to vaccination.Currently, other organisms such as bacteria, viruses, and fungi are the causes, especially among adults.nfectious is the most common. H influenzae type b was once the most common cause prior to vaccination. Currently, other organisms such as bacteria, viruses, and fungi are the causes, especially among adults.