Everyone's coming down with something at work and you can't afford to take a sick day. That, or you just don't want to catch it yourself. While there's not much you can do once you fall ill, there are steps you can take to minimise the risk and, hopefully, dodge the bug altogether.
As Alyse Kalish recommends over at The Muse, you'll want to make sure you have hand sanitiser easily available, especially when it's inconvenient to rush to the bathroom to wash your hands after every interaction.
If you're not in a position to take a few days off to avoid the plague, you can always encourage patient zero to take sick leave. Failing that, suggest they work from home if it's a practical option. Try to be diplomatic if you're going to give this a try -- the last thing you want to do is alienate the person.
Finally, if you have an office with some free space, you can relocate temporarily. Given the circumstances, your manager might be more accommodating of such a request.
And, if you do get sick -- best to follow your own advice.