why did carlisle change edward to vampire,what is edward's illness?

Edward and his parents were dying of Spanish Influenza...Edward's mother knew there was something special about Carlisle and she begged him to save Edward which he did by turning him into a vampire.

Edward, Edwards mother, and Edwards father were all sick in Carlisle's hospital. His father died first than before his mother died she new what Carlisle was and she said do whatever you can to save my Edward and she died than Carlisle turned Edward. Edward was sick because of the spanish influenza.