This might sound controversial but in my experience whether or not people call in sick can depend a lot on their job role and whether it can be done by other people. For example I've found in some places that some receptionists and nurses take time off freely for minor illness as they know the impact will be minor, ie someone else will do the the work while they are away. Obviously it impacts on the other people filling in and most people would take this into consideration and feel bad but there are always some who don't worry about it. However if one of the vets is sick it makes a huge difference, appointments have to be rescheduled, potentially surgeries too as the remaining vets already have a full work load and can't double up on appointments for example. So in my case although I'm sure people don't appreciate bugs being spread around if I'm sick, I think they get more annoyed at the inconvenience of having to rearrange things so I would never consider taking time off for a cold.