Answer:
In extreme cases, all of them.
The center of the swine flu viruses' attack is the respiratory system. Depending upon the degree of oxygen deprivation this might cause in the severe cases, all other systems can be affected by this lack of oxygenation. Some people get gastrointestinal symptoms and with fever, some, especially children can suffer seizures indicating an involvement of the neurological system. Dehydration from nausea and vomiting is often the first problem manifested that cause people to seek hospital care, and it can create problems with the kidneys and urinary and fluid balances. This can also cause ramifications with the circulatory system and heart. The immune system is affected as it attempts to attack the virus.
The most common cause of death is fluid in your lung and dehydration. The first reported death was from fluid-filled lungs. Pneumonia is one of the major complications in severe cases of the pandemic flu. It can be viral pneumonia, or it can be caused by a secondary bacterial infection.