The anecdote about Tiberias is drawn from Suetonius, who wrote "De Vita Caesarum," or more vulgarly known as "The Twelve Caesars."

Here is the excerpt (translation via the University of Chicago's website):

"He issued an edict forbidding general kissing, as well as the exchange of New Year's gifts after the Kalends of January. It was his custom to return a gift of four-fold value, and in person; but annoyed at being interrupted all through the month by those who did not have access to him on the holiday, he did not continue it."

Nothing in there about preventing STDS.