"An opportunistic infection is an infection caused by bacterial, viral, fungal, or protozoan pathogens that take advantage of a host with a weakened immune system or an altered microbiota (such as a disrupted gut flora). Many of these pathogens do not cause disease in a healthy host that has a normal immune system. A compromised immune system, however, presents an \"opportunity\" for the pathogen to infect."@en . "D009894" . "Opportunistic infection"@en .