Hi there!
I also applied to USC MPA, I submitted my application January 20th and I also recieved the email saying we would hear back late January/early February. I was also checking the mail like a maniac and got worried 7because I hadn't received anything yet. Yesterday (2/7) I called the admissions department just to make sure I had all my documents accounted for, they said yes I did and that I should probably hear something late February early March...so now apparently we just wait till then. Good Luck!