Initially, the illness resembles influenza with fever and a mild cough. The breathing disorder often progresses to severe shortness of breath (dyspnea) and inability to maintain oxygenation (hypoxia). Progression may be rapid, or it may take several days. Severely affected people develop a potentially fatal form of respiratory failure, known as adult respiratory distress syndrome (ARD or ARDS). In addition to attacking the alveoli in the lungs, the virus also infects other organs in the body, causing kidney failure, inflammation of the heart sac (pericarditis), or severe systemic bleeding from disruption of the clotting system (disseminated intravascular coagulation). People with compromised immune systems such as severe rheumatoid arthritis or organ transplantation may not experience respiratory symptoms but can have fever or diarrhea.