The most common site of adenovirus infection is the upper respiratory tract. Manifestations include symptoms of the common cold, pharyngitis, tonsillitis, otitis media, and pharyngoconjunctival fever. Life-threatening disseminated infection, severe pneumonia, meningitis, and encephalitis occur occasionally, especially among young infants and immunocompromised hosts. Adenoviruses occasionally cause acute hemorrhagic conjunctivitis, a pertussis-like syndrome, croup, bronchiolitis, exudative tonsillitis, pneumonia, or hemorrhagic cystitis. Enteric adenovirus serotypes cause gastroenteritis.