What disease was Edward dying of before he was changed?

In 1918, a Spanish Influenza (flu) epidemic hit our country hard, killing thousands of people. This is a true piece of history that Stephenie Meyer included in her work. Edward Masen and his family became sick like so many others across the country. However, their doctor was Carlisle Cullen. When Edward's mother Elizabeth was dying, she told Carlisle to save Edward, saying, "what others cannot do, that is what you must do for my Edward." Carlisle turned Edward into a vampire, as Edward was dying of the flu anyway. Today, we have medicines and vaccines that can usually prevent death from the flu, but back then if your body didn't naturally fight it off, you would die. Carlisle knew that Edward was dying, so he turned him, as per Elizabeth's dying wish. I am attaching an interesting site below so you can read about the real history behind the flu epidemic.