This problem ranks #1 and #2 in terms of co-worker issues as listed by the Society of Human Resources Management. Some suggestions I can offer include:
1. Bring up the issue with human resources but discussing it in private while being direct and wanting a resolution. Explain that this has become a long lasting issue and has resulted in workplace slowdown for example. Management at a higher level is what is needed in this case.
2. If management seems not to care, then sitting down with other co-workers and see as a group to sit down privately and offer support and guidance on your thoughts of getting a better smell out of this person. Let the office employee understand that you are not being mean but want to have a well run office environment. Being mean will not help so kindness along with being a bit direct can work.
3. See if moving the office employee if possible to another area that is away from others.
Everything I have been able to read on this issue offers these three ways to handle the situation. Article below goes into a bit more detail:
I hope these tips can help in getting rid of the smell that your co-worker seems to have. Please take a moment and rate my answer so that I know I was able to assist you and allow me to help other customers.