I did a little reading from the http://www.aphis.usda.gov/vs/trichinae/ ... _sheet.htm
This might help others to understand.
Where fresh pork is not tested for trichinae, as is the case in the U.S., alternative methods are used to prevent exposure of humans to potentially contaminated product. These include processing methods such as cooking, freezing and curing along with recommendations to the consumer concerning requirements for thorough cooking.
Cooking - Commercial preparation of pork products by cooking requires that meat be heated to internal temperatures which have been shown to inactivate trichinae. For example, Trichinella spiralis is killed in 47 minutes at 52° C (125.6° F), in 6 minutes at 55° C (131° F), and in < 1 minute at
60° C (140° F). It should be noted that these times and temperatures apply only when the product reaches and maintains temperatures evenly distributed throughout the meat. Alternative methods of heating, particularly the use of microwaves, have been shown to give different results, with parasites not completely inactivated when product was heated to reach a prescribed end-point temperature. The U.S. Code of Federal Regulations for processed pork products reflects experimental data, and requires pork to be cooked for 2 hours at 52.2° C (126° F), for 15 minutes at 55.6° C (132° F), and for 1 minute at 60° C (140° F).
The U.S. Department of Agriculture recommends that consumers of fresh pork cook the product to an internal temperature of 71° C or 160° F. Although this is considerably higher than temperatures at which trichinae are killed (about 55° C or 131° F), it allows for different methods of cooking which do not always result in even distribution of temperature throughout the meat. It should be noted that heating to 77° C (171° F) or 82° C (180° F) was not completely effective when cooking was performed using microwaves.
Freezing - Experiments have been performed to determine the effect of cold temperatures on the survival of T. spiralis in pork. Predicted times required to kill trichinae were 8 minutes at -20° C (-4° F), 64 minutes at -15° C (5° F), and 4 days at -10° C (14° F). Trichinae were killed instantaneously at -23.3° C (-10° F). The U.S. Department of Agriculture's Code of Federal Regulations, requires that pork intended for use in processed products be frozen at -17.8° C (0° F) for 106 hours, at -20.6° C (-5° F) for 82 hours, at -23.3° C (-10° F) for 63 hours, at -26.1° C
(-15° F) for 48 hours, at -28.9° C (-20° F) for 35 hours, at -31.7° C (-25° F) for 22 hours, at
-34.5° C (-30° F) for 8 hours, and at -37.2° C (-35° F) for 0.5 hours. These extended times take into account the amount of time required for temperature to equalize within the meat along with a margin of safety.
Curing - There are a great variety of processes used to prepare cured pork products (sausages, hams, pork shoulder, and other ready-to-eat products). Most processes currently used have been tested to determine their efficiency in killing trichinae. In the curing process, product is coated or injected with a salt mixture and allowed to equalize at refrigerated temperatures. Following equalization, product is dried or smoked and dried at various temperature/time combinations which have been shown to inactivate trichinae. The curing process involves the interaction of salt, temperature and drying times to reach a desired water activity, percent moisture, or brine concentration. Unfortunately, no single or even combination of parameters achieved by curing has been shown to correlate definitively with trichinae inactivation. All cured products should conform in process to one of many published regulations, such as the U.S. Department of Agriculture's Code of Federal Regulations Title 9, Chapter III, §318.10.