Most of the time, we think that conjunctivitis is caused when
bacteria on our hands is transmitted to the eyes when we rub our
eyes before washing our hands.
There are actually other ways of transmission, including airborne
droplets. 
If you or someone near
you sneezes, uh oh! 
However, the saving
grace is that airborne droplets from sneezing and / or coughing are
big, so they land faster than they remain airborne.
Which means, lots of surfaces we touch in public, may be
germ-laden. Eg. tap handles in public restrooms, doorknobs, lift
buttons, etc. Just be aware that you have to wash your hands and
wash them well before touching your eyes.
All said, none of us would get conjunctivitis too many times in our
lives. That's because once our body senses a 'germ invasion', our
auto-immune system immediately kicks in to eradicate the germs.
Besides, not all germs will be able to adapt to the conjunctiva
membrane and thrive there. Saving grace!
