More than 85% of the cases of LTB are caused by a virus. Parainfluenza 1, 2, and 3 viruses; respiratory syncytial virus; Mycoplasma pneumoniae; and rhinoviruses are the most common causes. The measles virus or bacterial infections such as pertussis and diphtheria are occasionally the cause. Epiglottitis, a life-threatening emergency caused by acute inflammation of the epiglottis and surrounding area, differs from LTB because it usually results from infection with the bacteria Haemophilus influenzae type B. Another rare occurrence is subglottic hemangioma, which can produce symptoms of croup initially. Recurrent croup may be associated with gastroesophageal reflux disease (GERD).