From what I've seen itcan be as high as 15-20% of bears (maybe more thats what the study I looked at said). Meat should be cooked to a minimium of 137F to kill the parasite. Here's what that same cooking site said about freezing :
"At 5° Fahrenheit, which is over 25° below freezing, for a piece of meat 6" or less, it takes 20 days to kill trichina. For a piece of meat more than 6" thick but less than 27" thick, it takes 30 days. The colder the temperature, the less time required. At negative 10°F, for a piece of meat 6" or less, it takes 10 days to kill trichina; for a piece of meat more than 6" thick but less than 27" thick, it takes 20 days. At negative 20°F below zero, for a piece of meat 6" or less, it takes 6 days to kill trichina, for a piece of meat more than 6" thick but less than 27" thick, it takes 12 days. The typical chest freezer should hold food at about 0°."
I wouldn't chance it and make sure it was cooked to at least 150F. (this is in my humble opinion)