Editing Infection (section)

===Colonization===
[[File:Dit del peu gros infectat.jpg|thumb|Infection of an [[ingrown nail|ingrown toenail]]; there is pus (yellow) and resultant inflammation (redness and swelling around the nail).]]
Infection begins when an organism successfully enters the body, grows and multiplies. This is referred to as colonization. Most humans are not easily infected. Those with compromised or weakened immune systems have an increased susceptibility to chronic or persistent infections. Individuals who have a suppressed [[immune system]] are particularly susceptible to [[opportunistic infection]]s. Entrance to the host at [[host–pathogen interface]], generally occurs through the [[Mucous membrane|mucosa]] in orifices like the [[oral cavity]], nose, eyes, genitalia, anus, or the microbe can enter through open wounds. While a few organisms can grow at the initial site of entry, many migrate and cause systemic infection in different organs. Some pathogens grow within the host cells (intracellular) whereas others grow freely in bodily fluids.<ref>{{Cite book |last=Peterson |first=Johnny W. |url=https://www.ncbi.nlm.nih.gov/books/NBK8526/ |title=Bacterial Pathogenesis |date=1996 |publisher=University of Texas Medical Branch at Galveston |language=en |pmid=21413346 |isbn=9780963117212 |access-date=2022-10-20 |archive-date=2016-04-25 |archive-url=https://web.archive.org/web/20160425080845/http://www.ncbi.nlm.nih.gov/books/NBK8526/ |url-status=live }}</ref>

[[Wound]] colonization refers to non-replicating microorganisms within the wound, while in infected wounds, replicating organisms exist and tissue is injured.<ref>{{Cite journal|last1=Negut|first1=Irina|last2=Grumezescu|first2=Valentina|last3=Grumezescu|first3=Alexandru Mihai|date=2018-09-18|title=Treatment Strategies for Infected Wounds|journal=Molecules |volume=23|issue=9|doi=10.3390/molecules23092392|issn=1420-3049|pmc=6225154|pmid=30231567|page=2392|doi-access=free}}</ref> All [[multicellular organism]]s are colonized to some degree by extrinsic organisms, and the vast majority of these exist in either a [[Mutualism (biology)|mutualistic]] or [[commensal]] relationship with the host. An example of the former is the [[Anaerobic organism|anaerobic bacteria]] species, which colonizes the [[mammal]]ian [[colon (anatomy)|colon]], and an example of the latter are the various species of [[staphylococcus]] that exist on [[human skin]]. Neither of these colonizations are considered infections. The difference between an infection and a colonization is often only a matter of circumstance. Non-pathogenic organisms can become pathogenic given specific conditions, and even the most [[virulent]] organism requires certain circumstances to cause a compromising infection. Some colonizing bacteria, such as ''[[Corynebacteria]] sp.'' and ''[[Viridans streptococci]]'', prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic relationship with the host, preventing infection and speeding [[wound healing]].
[[File:Pathogenic Infection.png|thumb|This image depicts the steps of pathogenic infection.<ref>{{Cite journal |last1=Duerkop |first1=Breck A |last2=Hooper |first2=Lora V |date=2013-07-01 |title=Resident viruses and their interactions with the immune system |journal=Nature Immunology |language=en |volume=14 |issue=7 |pages=654–59 |doi=10.1038/ni.2614 |pmc=3760236 |pmid=23778792}}</ref><ref>{{Cite web |title=Bacterial Pathogenesis at Washington University |url=https://www.studyblue.com/notes/note/n/bacterial-pathogenesis/deck/11094651 |access-date=2016-12-02 |website=StudyBlue |location=St. Louis |archive-date=2016-12-03 |archive-url=https://web.archive.org/web/20161203060624/https://www.studyblue.com/notes/note/n/bacterial-pathogenesis/deck/11094651 |url-status=live }}</ref><ref>{{Cite web |title=Print Friendly |url=http://www.lifeextension.com/magazine/2014/6/the-dangers-of-using-antibiotics-to-prevent-urinary-tract-infections/page-01?p=1 |url-status=dead |archive-url=https://web.archive.org/web/20161202235200/http://www.lifeextension.com/magazine/2014/6/the-dangers-of-using-antibiotics-to-prevent-urinary-tract-infections/page-01?p=1 |archive-date=2016-12-02 |access-date=2016-12-02 |website=www.lifeextension.com}}</ref>]]
The variables involved in the outcome of a host becoming inoculated by a pathogen and the ultimate outcome include:
* the route of entry of the [[pathogen]] and the access to host regions that it gains
* the intrinsic [[virulence]] of the particular organism
* the quantity or load of the initial inoculant
* the [[immune system|immune]] status of the host being colonized

As an example, several [[staphylococcus|staphylococcal]] species remain harmless on the skin, but, when present in a normally [[sterile technique|sterile]] space, such as in the capsule of a [[joint]] or the [[peritoneum]], multiply without resistance and cause harm.<ref>{{Cite journal |last1=Tong |first1=Steven Y. C. |last2=Davis |first2=Joshua S. |last3=Eichenberger |first3=Emily |last4=Holland |first4=Thomas L. |last5=Fowler |first5=Vance G. |date=2015 |title=Staphylococcus aureus Infections: Epidemiology, Pathophysiology, Clinical Manifestations, and Management |journal=Clinical Microbiology Reviews |volume=28 |issue=3 |pages=603–661 |doi=10.1128/CMR.00134-14 |issn=0893-8512 |pmc=4451395 |pmid=26016486}}</ref>

An interesting fact that [[gas chromatography–mass spectrometry]], [[16S ribosomal RNA]] analysis, [[omics]], and other advanced technologies have made more apparent to humans in recent decades is that microbial colonization is very common even in environments that humans think of as being nearly [[asepsis|sterile]]. Because it is normal to have bacterial colonization, it is difficult to know which chronic wounds can be classified as infected and how much risk of progression exists. Despite the huge number of wounds seen in clinical practice, there are limited quality data for evaluated symptoms and signs. A review of chronic wounds in the [[JAMA|Journal of the American Medical Association]]'s "Rational Clinical Examination Series" quantified the importance of increased pain as an indicator of infection.<ref>{{cite journal |vauthors=Reddy M, Gill SS, Wu W | date = Feb 2012 | title = Does this patient have an infection of a chronic wound? | journal = JAMA | volume = 307 | issue = 6| pages = 605–11 | doi = 10.1001/jama.2012.98 | pmid = 22318282 |display-authors=etal}}</ref> The review showed that the most useful finding is an increase in the level of pain [likelihood ratio (LR) range, 11–20] makes infection much more likely, but the absence of pain (negative likelihood ratio range, 0.64–0.88) does not rule out infection (summary LR 0.64–0.88).

{{anchor|Persistent infection}}