What prompt the people of Thebes and the priest to come to the palace at the beginning of the play

The play opens in front of Oedipus' palace at Thebes. A plague besets the city, and Oedipus enters to find a priest and crowd of children praying to the gods to free them from the curse. A blight, the priest tells Oedipus, has destroyed their crops and livestock - and even rendered their women sterile, unable to have children.