Further, people may start associating you with the negativity even if you're just listening and not participating. There is a danger that your office mates may start attributing you as the source.
So how should you deal with your negative colleague? The WSJ recommends to just switch the topic and respond with a question about work that will elicit a positive answer, such as, "What's going well at work?"
How do you deal with downer co-workers?