Rupture of the trachea or bronchus is the most common type of blunt injury to the airway.[15] It is difficult to determine the incidence of TBI: in as many as 30–80% of cases, death occurs before the person reaches a hospital, and these people may not be included in studies.[3] On the other hand, some TBI are so small that they do not cause significant symptoms and are therefore never noticed.[29] In addition, the injury sometimes is not associated with symptoms until complications develop later, further hindering estimation of the true incidence.[6] However, autopsy studies have revealed TBI in 2.5–3.2% of people who died after trauma.[3] Of all neck and chest traumas, including people that died immediately, TBI is estimated to occur in 0.5–2%.[29] An estimated 0.5% of polytrauma patients treated in trauma centers have TBI.[14] The incidence is estimated at 2% in blunt chest and neck trauma and 1–2% in penetrating chest trauma.[14] Laryngotracheal injuries occur in 8% of patients with penetrating injury to the neck, and TBI occurs in 2.8% of blunt chest trauma deaths.[6] In people with blunt trauma who do reach a hospital alive, reports have found incidences of 2.1% and 5.3%.[2] Another study of blunt chest trauma revealed an incidence of only 0.3%, but a mortality rate of 67% (possibly due in part to associated injuries).[6] The incidence of iatrogenic TBI (that caused by medical procedures) is rising, and the risk may be higher for women and the elderly.[30] TBI results about once every 20,000 times someone is intubated through the mouth, but when intubation is performed emergently, the incidence may be as high as 15%.[30]