at hospital 

Nosocomial infection - Hospital acquired infection- its infected through medical device- from one patient to another 

you have something that normal in one place 

opportunistic infection -

chemotherapy patient, AIDS patient, 

The right bacteria at the wrong place caused serious harm to the host. 

Exogenous - originate outside the body (example lots of parasite or other infections microbes)

 Staphylococcus Epidermis