An<unk>  is an<unk>  caused by pathogens, particularly<unk>  pathogens - those that take advantage of certain situations - such as bacterial, viral, fungal, or protozoan<unk> s that usually do not cause disease in a healthy host, one with a healthy immune system. A compromised immune system, however, presents an "opportunity" for the pathogen to infect.
Opportunistic infection
Blood-borne disease
Superinfection
Spontaneous process
Nosocomial infection
Sexually transmitted disease
Antibiotic resistance
Moral hazard