Is it 100% guarantee that you can get a staff infection after you had a contact?

Some people are just carriers and do not know they have it. Being in the same room you most probably won't get it unless you come in direct contact with the bacteria.
In the jail near where I live they have had inmates die from staph in the shower. All the inmates use the shower but only a small percentage get the staph.
Antibiotic Resistance Web Site

It's staph, not "staff". There's a big problem in the U.S. with staph infections breaking out in nursing homes, hospitals, and now even schools, colleges, etc.

Everyone carries staph bacteria but for most it's harmless. Washing hands thoroughly, taking care of open wounds on arms, legs, and feet (even just scratches), and not sharing cups and glasses will prevent outbreaks. If you have a pimple or sore that won't heal, see your doctor about it.