Editing Infection (section)

===== Opportunistic pathogens =====

{{main|Opportunistic infection}}
Opportunistic pathogens can cause an infectious disease in a host with depressed resistance ([[immunodeficiency]]) or if they have unusual access to the inside of the body (for example, via [[Major trauma|trauma]]). [[Opportunistic infection]] may be caused by microbes ordinarily in contact with the host, such as [[pathogenic bacteria]] or fungi in the [[gastrointestinal]] or the [[upper respiratory tract]], and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in ''[[Clostridioides difficile]]'' [[colitis]]) or from the environment as a result of [[Physical trauma|traumatic]] introduction (as in [[surgical]] wound infections or [[compound fracture]]s). An opportunistic disease requires impairment of host defenses, which may occur as a result of [[genetic defect]]s (such as [[chronic granulomatous disease]]), exposure to [[antimicrobial]] drugs or [[immunosuppressive]] chemicals (as might occur following [[poison]]ing or [[cancer]] [[chemotherapy]]), exposure to [[ionizing radiation]], or as a result of an infectious disease with immunosuppressive activity (such as with [[measles]], [[malaria]] or [[HIV disease]]). Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host.<ref name=Sherris/>