Editing Infection (section)

====Primary versus opportunistic====

{{See also|Coinfection}}
{{anchor|Primary versus secondary}}<!-- This section is linked from Primary infection, Secondary infection and Acute infection-->
Among the many varieties of [[microorganisms]], relatively few cause disease in otherwise healthy individuals.<ref name=Baron>This section incorporates [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed public domain] {{Webarchive|url=https://web.archive.org/web/20090629132331/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed |date=2009-06-29 }} materials included in the text: [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=mmed.TOC&depth=10 Medical Microbiology] {{Webarchive|url=https://web.archive.org/web/20090701213330/https://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=mmed.TOC&depth=10 |date=2009-07-01 }} Fourth Edition: [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.594 Chapter 8] {{Webarchive|url=https://web.archive.org/web/20090219005050/https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.594 |date=2009-02-19 }} (1996). Baron, Samuel MD. The University of Texas Medical Branch at Galveston. {{cite book |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed |title=Medical Microbiology |access-date=2013-11-27 |url-status=live |archive-url=https://web.archive.org/web/20090629132331/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed |archive-date=June 29, 2009 |isbn=9780963117212 |publisher=University of Texas Medical Branch at Galveston |year=1996 |pmid=21413252 |last1=Baron |first1=S. }}</ref> Infectious disease results from the interplay between those few [[pathogen]]s and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depend upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. However, a host's immune system can also cause damage to the host itself in an attempt to control the infection. Clinicians, therefore, classify infectious microorganisms or microbes according to the status of host defenses – either as ''primary pathogens'' or as ''[[opportunistic infection|opportunistic pathogens]]''.<ref name="pmid29135922">{{cite journal |vauthors=Patil NK, Guo Y, Luan L, Sherwood ER |title=Targeting Immune Cell Checkpoints during Sepsis |journal=International Journal of Molecular Sciences |volume=18 |issue=11 |date=November 2017 |page=2413 |pmid=29135922 |pmc=5713381 |doi=10.3390/ijms18112413 |url=|doi-access=free }}</ref>

===== Primary pathogens =====
Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic [[virulence]] (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans, however, many serious diseases are caused by organisms acquired from the environment or that infect non-human hosts.<ref name="pmid31027668">{{cite journal |vauthors=McArthur DB |title=Emerging Infectious Diseases |journal=The Nursing Clinics of North America |volume=54 |issue=2 |pages=297–311 |date=June 2019 |pmid=31027668 |pmc=7096727 |doi=10.1016/j.cnur.2019.02.006 |url=}}</ref>

===== 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/>

===== Secondary infection =====
While a primary infection can practically be viewed as the [[root cause analysis|root cause]] of an individual's current health problem, a secondary infection is a [[sequela]] or [[complication (medicine)|complication]] of that root cause. For example, an infection due to a [[burn]] or [[penetrating trauma]] (the root cause) is a secondary infection. Primary pathogens often cause primary infection and often cause secondary infection. Usually, opportunistic infections are viewed as secondary infections (because immunodeficiency or [[injury]] was the predisposing factor).<ref name="pmid29135922"/>

===== Other types of infection =====
Other types of infection consist of mixed, [[Iatrogenic infections|iatrogenic]], [[Hospital-acquired infection|nosocomial]], and community-acquired infection. A mixed infection is an infection that is caused by two or more pathogens. An example of this is [[appendicitis]], which is caused by ''[[Bacteroides fragilis]]'' and ''[[Escherichia coli]]''. The second is an iatrogenic infection. This type of infection is one that is transmitted from a health care worker to a patient. A nosocomial infection is also one that occurs in a health care setting. Nosocomial infections are those that are acquired during a hospital stay. Lastly, a community-acquired infection is one in which the infection is acquired from a whole community.<ref name=":0" />