As with any poultry, there’s always the chance that duck harbors harmful bacteria. But cooking duck is different than cooking chicken and turkey because it’s actually a red meat. As with other red meats, some people prefer to eat duck that's cooked medium or medium rare so it’s still pink inside.
The official food safety word from the USDA is that duck breast should be cooked to at least 160°F and preferably to 170°F. If you cook a duck breast to 155°F (assuming that carryover cooking will continue to raise the temperature to 160°F as the duck rests), it will be medium well—safe to eat and still a little pink in the center, but perhaps a tad drier than you might like. If you’re pregnant or if you have a compromised immune system, this is the route you should take.
But if you prefer your duck a little pinker, cook it to 135° or 140°F and enjoy a medium-rare to medium duck breast. It isn’t guaranteed safe, but if you like your duck a little more juicy and tender, you might consider the slight risk to be worthwhile.