In Sophocles' Oedipus Rex, to what does the priest compare the troubles that face Thebes in the opening of the play?

In his
opening speech, the priest compares
Thebes' present plague to the troubled times the city was in the midst of whenfirst came to
Thebes. Years ago, the city was being plagued by a Sphinx.
According to Greek mythology, a Sphinx is a creature that has a lion's body, bird's wings, and a
woman's face. It speaks in riddles and whomever it approaches that cannot answer the riddle is
eaten alive. According to legend, a Sphinx was sent to Thebes by the gods as a plague
andpromised to make king anyone who could solve the Sphinx's riddle ( href="https://www.theoi.com/Ther/Sphinx.html" title=""Sphinx,"
theoi.com">"Sphinx," theoi.com). Since Oedipus rescued the city from
the Sphinx so many years ago, the priest is begging Oedipus to rescue them from their present
plague, thereby comparing both plagues.

We see
the priest allude to this past plague in his lines:

It was
you who came and released Cadmus' town
from the tribute we paid to the cruel
songstress,
and these things you did knowing nothing from us,
nor instructed
at all, but with help from god
you spoke and knew how to set out lives straight.
(39-43)

Hence, since the priest believes that Oedipus was
sent by the gods to rescue them from the Sphinx, he believes that with the help of the gods
Oedipus can heal the present plague.