Usually take the bus to work, in the spring and summer... but not during cold and flu season.
Being on public transit is perhaps one of the worst places a person should be if they are wanting to avoid getting sick - particularly so if there is a pandemic or severe flu going around. Getting the shots isn't 100%, so one must take other reasonable precautions as well.
Don't get me wrong, I'm not a hypochondriac... but, rather, just a keen observer of people. On the buses - with no windows open during the cold months, of course - you will see all sorts of people gladly hacking out a lung into the air for all to breath in. Too many make zero effort to cover their cough. In fact, such people are no better than the sick swine who started this filthy flu... I'd even say that I have more respect for the pigs, as they are expected to act like animals.