Epiglottitis is the inflammation of the epiglottis—the flap at the base of the tongue that prevents food entering the trachea (windpipe). Symptoms are usually rapid in onset and include trouble swallowing which can result in drooling, changes to the voice, fever, and an increased breathing rate. As the epiglottis is in the upper airway, swelling can interfere with breathing. People may lean forward in an effort to open the airway. As the condition worsens, stridor and bluish skin may occur.

Epiglottitis was historically mostly caused by infection by H. influenzae type b (commonly referred to as "Hib"). Following the introduction of the Hib vaccine, pediatric cases of epiglottitis fell from 3.47 cases per 100,000 children in 1980 to 0.63 cases in 1990 such that it is now more often caused by other bacteria, most commonly Streptococcus pneumoniae, Streptococcus pyogenes, or Staphylococcus aureus. Predisposing factors include burns and trauma to the area. The most accurate way to make the diagnosis is to look directly at the epiglottis. X-rays of the neck from the side may show a "thumbprint sign" but the lack of this sign does not mean the condition is absent.

An effective vaccine, the Hib vaccine, has been available since the 1980s. The antibiotic rifampicin may also be used to prevent the disease among those who have been exposed to the disease and are at high risk. The most important part of treatment involves securing the airway, which is often done by endotracheal intubation. Intravenous antibiotics such as ceftriaxone and possibly vancomycin or clindamycin is then given. Corticosteroids are also typically used. With appropriate treatment, the risk of death among children with the condition is about one percent and among adults is seven percent.

With the use of the Hib vaccine, the number of cases of epiglottitis has decreased by more than 95%. Historically, young children were mostly affected, but it is now more common among older children and adults. In the United States, pediatric cases of epiglottitis fell from 3.47 cases per 100,000 children in 1980 to 0.63 cases in 1990 following the introduction of the Hib vaccinae, and it now affects about 1.3 per 100,000 children a year. In adults, between 1 and 4 per 100,000 are affected a year. It occurs more commonly in the developing world. In children the risk of death is about 6%; however, if they are intubated early, it is less than 1%.

Epiglottitis is associated with fever, throat pain, difficulty in swallowing, drooling, hoarseness of voice, and stridor. Onset is typically over a day. The throat itself may appear normal.

Stridor is a sign of upper airway obstruction and is a surgical emergency. The child often appears acutely ill, anxious, and will have very quiet shallow breathing often keeping the head held forward and insisting on sitting up in bed, commonly called the "tripod position." The early symptoms are usually insidious but rapidly progressive, and swelling of the throat may lead to cyanosis and asphyxiation.

Adults commonly present with less dramatic breathing symptoms than children due to them having wider airways to begin with, so their main symptoms are usually a severe sore throat and difficulty swallowing. The back of the throat appears normal in 90% of adult patients, so epiglottitis should considered when there is pain out of proportion to exam or when pain is caused by pressing on the external windpipe. Adult epiglottitis is often referred to as supraglottitis. In contrast to children, the symptoms are non-specific, sub-acute and can be unpredictable.

Epiglottitis is primarily caused by an acquired bacterial infection of the epiglottis. Historically it was most often caused by Haemophilus influenzae type B, but with the availability of immunization this is no longer the case. H. influenzae type B contains a capsule which helps it avoid being destroyed by macrophages and also contains surface proteins that allow it to stick to the lining of the upper respiratory tract. Presently, the bacteria most often causing infection are other encapsulated organisms including Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus. These bacteria spread in respiratory droplets or aerosols produced from coughing and sneezing. While the overall incidence of epiglottitis has decreased, the incidence of cases caused by Streptococcus pneumoniae has increased in adults. The exact strains of Streptococcus pneumoniae are often those that are covered by the PPV-23 vaccine, but there is no evidence that this vaccine prevents epiglottitis.