In later stages, changes in the architecture of the lung, such as pathology in the major airways (bronchiectasis), further exacerbate difficulties in breathing. Other signs include coughing up blood (hemoptysis), high blood pressure in the lung (pulmonary hypertension), heart failure, difficulties getting enough oxygen to the body (hypoxia), and respiratory failure requiring support with breathing masks, such as bilevel positive airway pressure machines or ventilators. "Staphylococcus aureus", "Haemophilus influenzae", and "Pseudomonas aeruginosa" are the three most common organisms causing lung infections in CF patients. In addition, opportunistic infection due to "Burkholderia cepacia" complex can occur, especially through transmission from patient to patient. The most common infection involves bacterial strain mutation to form a biofilm-forming and sustaining mucoid strain on the lung epithelium, which can result in downstream mechanisms that progress the infection. In addition to typical bacterial infections, people with CF more commonly develop other types of lung diseases.