The transmission of the hepatitis A virus occurs primarily through person to person contact via the fecal-oral (meaning from stools to mouth) route. So let's say this patient uses the toilet, and you use it after him and do not wash your hands thoroughly, then you eat, you may get the virus. Mind you, if you have received the hepatitis A vaccine adult booster dose, then you should not worry that much because you're most likely protected (you have antibodies in your system against the virus).
Viral shedding persists for 1 to 3 weeks. Infected persons are most likely to transmit hepatitis A virus 1 to 2 weeks before the onset of illness, when the virus' concentration in stool is highest. The risk then decreases and is minimal the week after the onset of jaundice. In principle, since your colleague has had obvious symptoms since December 3rd (more than 2 weeks ago), then he's most likely no longer shedding the virus at this point.
To be safe, avoid sharing food utensils (mugs, dishes, etc) and the toilet with the person in question for the next week or so. I also encourage you to contact his treating physician to get the exact and correct information about his condition to avoid unnecessary panic.