Salmonella is the main risk with uncooked eggs, and salmonella more often is caused by undercooked yolks than in whites. In many countries in Europe, chickens are vaccinated against salmonella; in the US, they are not. Eggs in the US are washed, but not in Europe. Heating the egg whites and sugar in a double boiler to 160 degrees F (71 degrees C) will kill any potential salmonella. You can also use pre-packaged pasteurized egg whites as mentioned above, which have already been heated to kill any pathogens. I find that the pre-packaged pasteurized egg whites do not whip up as fluffy as fresh whites so I tend to use a combination of the two (at least 25% fresh). That means that I still heat them to 160 degrees F. If you use only the pasteurized egg whites, you just need to heat the egg whites and sugar enough to thoroughly dissolve the sugar, a much lower temperature.
http://www.forbes.com/sites/nadiaarumugam/2012/10/25/why-american-eggs-would-be-illegal-in-a-british-supermarket-and-vice-versa/
