Title: Methicillin-resistant Staphylococcus aureus

{{Short description|Bacterium responsible for difficult-to-treat infections in humans}}
{{Redirect|MRSA}}
{{cs1 config|name-list-style=vanc|display-authors=6}}{{Italic title|string=Staphylococcus aureus}}
[[File:Human neutrophil ingesting MRSA.jpg|thumb|alt=Colorized scanning electron micrograph of a human neutrophil ingesting MRSA|Colorized [[scanning electron micrograph]] of a human [[Neutrophil granulocyte|neutrophil]] ingesting MRSA]]
'''Methicillin-resistant ''Staphylococcus aureus''''' ('''MRSA''') is a group of [[gram-positive bacteria]] that are genetically distinct from other [[strain (biology)|strains]] of ''[[Staphylococcus aureus]]''. MRSA is responsible for several difficult-to-treat [[infection]]s in humans. It caused more than 100,000 deaths worldwide attributable to [[antimicrobial resistance]] in 2019.

MRSA is any strain of ''S. aureus'' that has developed (through [[mutation]]) or acquired (through [[horizontal gene transfer]]) a [[multiple drug resistance]] to [[beta-lactam antibiotics]]. Beta-lactam (β-lactam) antibiotics are a [[broad-spectrum antibiotic|broad-spectrum group]] that include some [[penam]]s ([[penicillin]] derivatives such as [[methicillin]] and [[oxacillin]]) and [[cephem]]s such as the [[cephalosporin]]s.&lt;ref name=&quot;CochraneSurg2013&quot; /&gt; Strains unable to resist these antibiotics are classified as methicillin-susceptible ''S. aureus'', or MSSA.

MRSA infection is common in hospitals, prisons, and nursing homes, where people with open [[wound]]s, invasive devices such as [[catheter]]s, and weakened [[immune system]]s are at greater risk of [[hospital-acquired infection|healthcare-associated infection]]. MRSA began as a hospital-acquired infection but has become community-acquired, as well as livestock-acquired. The terms HA-MRSA (healthcare-associated or hospital-acquired MRSA), CA-MRSA (community-associated MRSA), and LA-MRSA (livestock-associated MRSA) reflect this.

== Signs and symptoms ==
[[File:Mrsa2.jpg|thumb|Although usually carried without symptoms, MRSA often presents as small red pustular skin infections]]

In humans, ''Staphylococcus aureus'' is part of the normal [[microbiota]] present in the upper respiratory tract,&lt;ref name=URTmicribiome2016rev&gt;{{cite journal | vauthors = Schenck LP, Surette MG, Bowdish DM | title = Composition and immunological significance of the upper respiratory tract microbiota | journal = FEBS Letters | volume = 590 | issue = 21 | pages = 3705–3720 | date = November 2016 | pmid = 27730630 | doi = 10.1002/1873-3468.12455 | pmc = 7164007 }}&lt;/ref&gt; and on skin and in the gut mucosa.&lt;ref&gt;{{cite journal | vauthors = Wollina U | title = Microbiome in atopic dermatitis | journal = Clinical, Cosmetic and Investigational Dermatology | volume = 10 | pages = 51–56 | date = 2017 | pmid = 28260936 | pmc = 5327846 | doi = 10.2147/CCID.S130013 | doi-access = free }}&lt;/ref&gt; However, along with similar bacterial species that can colonize and act symbiotically, they can cause disease if they begin to take over the tissues they have colonized or invade other tissues; the resultant infection has been called a &quot;pathobiont&quot;.&lt;ref name=URTmicribiome2016rev /&gt;

After 72 hours, MRSA can take hold in human tissues and eventually become resistant to treatment. The initial presentation of MRSA is small red bumps that resemble pimples, spider bites, or boils; they may be accompanied by fever and, occasionally, rashes. Within a few days, the bumps become larger and more painful; they eventually open into deep, pus-filled boils. About 75 percent of CA-MRSA infections are localized to skin and soft tissue and usually can be treated effectively.&lt;ref name=IDSA2011 /&gt;

== Risk factors ==
A select few of the populations at risk include:
* People with indwelling implants, prostheses, drains, and catheters&lt;ref name = CochraneSurg2013 /&gt;&lt;ref name = Sga2016 /&gt;
* People who are frequently in crowded places, especially with shared equipment and skin-to-skin contact&lt;ref name=riskfactors&gt;{{cite web |url=https://www.cdc.gov/mrsa/community/index.html |title=General Information About MRSA in the Community |access-date=9 October 2014 |publisher=[[Centers for Disease Control and Prevention]] |date=10 September 2013}}&lt;/ref&gt;
* People with weak immune systems ([[HIV]]/[[AIDS]], [[lupus]], or [[cancer]] patients; [[organ transplantation|transplant]] recipients; severe [[asthma]]tics; primary immune deficiencies , etc.)
* [[Diabetes|Diabetics]]&lt;ref name = CochraneSurg2013 /&gt;&lt;ref&gt;{{cite journal | vauthors = Lipsky BA, Tabak YP, Johannes RS, Vo L, Hyde L, Weigelt JA | s2cid = 5660826 | title = Skin and soft tissue infections in hospitalised patients with diabetes: culture isolates and risk factors associated with mortality, length of stay and cost | journal = Diabetologia | volume = 53 | issue = 5 | pages = 914–23 | date = May 2010 | pmid = 20146051 | doi = 10.1007/s00125-010-1672-5 | doi-access = free }}&lt;/ref&gt;
* [[Intravenous drug]] users&lt;ref&gt;{{cite journal | vauthors = Otter JA, French GL | title = Community-associated meticillin-resistant Staphylococcus aureus strains as a cause of healthcare-associated infection | journal = The Journal of Hospital Infection | volume = 79 | issue = 3 | pages = 189–93 | date = November 2011 | pmid = 21741111 | doi = 10.1016/j.jhin.2011.04.028 }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Kluytmans-Vandenbergh MF, Kluytmans JA | title = Community-acquired methicillin-resistant Staphylococcus aureus: current perspectives | journal = Clinical Microbiology and Infection | volume = 12 | issue = Suppl 1 | pages = 9–15 | date = March 2006 | pmid = 16445719 | doi = 10.1111/j.1469-0691.2006.01341.x | doi-access = free }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Golding GR, Quinn B, Bergstrom K, Stockdale D, Woods S, Nsungu M, Brooke B, Levett PN, Horsman G, McDonald R, Szklarczuk B, Silcox S, Paton S, Carson M, Mulvey MR, Irvine J | title = Community-based educational intervention to limit the dissemination of community-associated methicillin-resistant Staphylococcus aureus in Northern Saskatchewan, Canada | journal = BMC Public Health | volume = 12 | issue = 1 | article-number = 15 | date = January 2012 | pmid = 22225643 | pmc = 3287965 | doi = 10.1186/1471-2458-12-15 | doi-access = free }}&lt;/ref&gt;
* Regular contact with someone who has injected drugs in the past year&lt;ref name=&quot;Loewen 512–520&quot;&gt;{{cite journal | vauthors = Loewen K, Schreiber Y, Kirlew M, Bocking N, Kelly L | title = Community-associated methicillin-resistant ''Staphylococcus aureus'' infection: Literature review and clinical update | journal = Canadian Family Physician | volume = 63 | issue = 7 | pages = 512–520 | date = July 2017 | pmid = 28701438 | pmc = 5507223 }}&lt;/ref&gt;
* Users of [[quinolone antibiotic]]s&lt;ref name = Sga2016 /&gt;&lt;ref name=tacconelli2008&gt;{{cite journal | vauthors = Tacconelli E, De Angelis G, Cataldo MA, Pozzi E, Cauda R | title = Does antibiotic exposure increase the risk of methicillin-resistant Staphylococcus aureus (MRSA) isolation? A systematic review and meta-analysis | journal = The Journal of Antimicrobial Chemotherapy | volume = 61 | issue = 1 | pages = 26–38 | date = January 2008 | pmid = 17986491 | doi = 10.1093/jac/dkm416 | doi-access = free }}&lt;/ref&gt;
* Elderly people&lt;ref name=Sga2016&gt;{{cite journal | vauthors = Sganga G, Tascini C, Sozio E, Carlini M, Chirletti P, Cortese F, Gattuso R, Granone P, Pempinello C, Sartelli M, Colizza S | title = Focus on the prophylaxis, epidemiology and therapy of methicillin-resistant Staphylococcus aureus surgical site infections and a position paper on associated risk factors: the perspective of an Italian group of surgeons | journal = World Journal of Emergency Surgery | volume = 11 | issue = 1 | article-number = 26 | year = 2016 | pmid = 27307786 | pmc = 4908758 | doi = 10.1186/s13017-016-0086-1 | doi-access = free }}&lt;/ref&gt;&lt;ref name=Dumyati2017 /&gt;
* School children sharing sports and other equipment
* College students living in dormitories&lt;ref name=riskfactors /&gt;
* People staying or working in a health-care facility for an extended period&lt;ref name = Sga2016 /&gt;&lt;ref name=riskfactors /&gt;
* People who spend time in coastal waters where MRSA is present, such as some beaches in [[Florida]] and the [[West Coast of the United States]]&lt;ref name=florida&gt;{{cite news |url=https://www.foxnews.com/story/study-beachgoers-more-likely-to-catch-mrsa |agency=Reuters |publisher=[[Fox Entertainment Group|FoxNews.com]] |title=Study: Beachgoers More Likely to Catch MRSA |date=2009-02-16}}&lt;/ref&gt;&lt;ref name=AP1&gt;{{cite news |url=https://www.foxnews.com/story/dangerous-staph-germs-found-at-west-coast-beaches | vauthors = Marchione M |agency=Associated Press |title=Dangerous staph germs found at West Coast beaches |date=2009-09-12}}&lt;/ref&gt;
* People who spend time in confined spaces with other people, including occupants of homeless shelters, [[prison]] inmates, and military recruits in [[recruit training|basic training]]&lt;ref name=soldiers&gt;{{cite journal | vauthors = Zinderman CE, Conner B, Malakooti MA, LaMar JE, Armstrong A, Bohnker BK | title = Community-acquired methicillin-resistant Staphylococcus aureus among military recruits | journal = Emerging Infectious Diseases | volume = 10 | issue = 5 | pages = 941–4 | date = May 2004 | pmid = 15200838 | pmc = 3323224 | doi = 10.3201/eid1005.030604 | url = http://www.medscape.com/viewarticle/474843 }}&lt;/ref&gt;&lt;ref name=&quot;The University of Chicago Medical Center&quot; /&gt;
* Veterinarians, livestock handlers, and pet owners&lt;ref name=cmr&gt;{{cite journal | vauthors = David MZ, Daum RS | title = Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic | journal = Clinical Microbiology Reviews | volume = 23 | issue = 3 | pages = 616–87 | date = July 2010 | pmid = 20610826 | pmc = 2901661 | doi = 10.1128/CMR.00081-09 }}&lt;/ref&gt;
* People who ingest unpasteurized milk&lt;ref name = Gopal2017 /&gt;
* People who are immunocompromised and also colonized&lt;ref name=Ficalora /&gt;{{rp|249}}
* People with [[chronic obstructive pulmonary disease]]&lt;ref name =Sga2016 /&gt;
* People who have had thoracic surgery&lt;ref name = Sga2016 /&gt;

As many as 22% of people colonised with MRSA do not have any discernible risk factors.&lt;ref name=Winn /&gt;{{rp|637}}

=== Hospitalized people ===
People who are hospitalized, including the elderly, are often [[immunocompromised]] and susceptible to infection of all kinds, including MRSA; an infection by MRSA is called healthcare-associated or hospital-acquired methicillin-resistant ''S. aureus'' (HA-MRSA).&lt;ref name= CochraneSurg2013 /&gt;&lt;ref name = Sga2016 /&gt;&lt;ref name=CochraneNonSurg2013&gt;{{cite journal | vauthors = Gurusamy KS, Koti R, Toon CD, Wilson P, Davidson BR | title = Antibiotic therapy for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) in non surgical wounds | journal = The Cochrane Database of Systematic Reviews | issue = 11 | article-number = CD010427 | date = November 2013 | pmid = 24242704 | doi = 10.1002/14651858.CD010427 | veditors = Gurusamy KS | url = http://cochranelibrary-wiley.com/doi/10.1002/14651858.CD010427/pdf | pmc = 11299151 }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Jacobs A | title = Hospital-acquired methicillin-resistant Staphylococcus aureus: status and trends | journal = Radiologic Technology | volume = 85 | issue = 6 | pages = 623–48; quiz 649–52 | date = 2014 | pmid = 25002642 }}&lt;/ref&gt;
Generally, those infected by MRSA stay infected for just under 10 days, if treated by a doctor, although effects may vary from person to person.&lt;ref&gt;{{cite web |title=Is MRSA Contagious? |url=http://www.medicinenet.com/is_mrsa_contagious/article.htm |access-date=24 October 2017 |website=Medicinenet.com |vauthors=Davis C}}&lt;/ref&gt;

Both surgical and nonsurgical wounds can be infected with HA-MRSA.&lt;ref name= CochraneSurg2013&gt;{{cite journal | vauthors = Gurusamy KS, Koti R, Toon CD, Wilson P, Davidson BR | title = Antibiotic therapy for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in surgical wounds | journal = The Cochrane Database of Systematic Reviews | issue = 8 | article-number = CD009726 | date = August 2013 | pmid = 23963687 | doi = 10.1002/14651858.CD009726.pub2 | pmc = 11301404 }}&lt;/ref&gt;&lt;ref name = Sga2016 /&gt;&lt;ref name=CochraneNonSurg2013 /&gt; Surgical site infections occur on the skin surface, but can spread to internal organs and blood to cause [[sepsis]].&lt;ref name=CochraneSurg2013 /&gt; Transmission can occur between healthcare providers and patients because some providers may neglect to perform preventative hand-washing between examinations.&lt;ref name=tacconelli2008 /&gt;&lt;ref name=muto2003 /&gt;

People in [[nursing home]]s are at risk for all the reasons above, further complicated by their generally weaker immune systems.&lt;ref name=Dumyati2017&gt;{{cite journal | vauthors = Dumyati G, Stone ND, Nace DA, Crnich CJ, Jump RL | title = Challenges and Strategies for Prevention of Multidrug-Resistant Organism Transmission in Nursing Homes | journal = Current Infectious Disease Reports | volume = 19 | issue = 4 | article-number = 18 | date = April 2017 | pmid = 28382547 | pmc = 5382184 | doi = 10.1007/s11908-017-0576-7 }}&lt;/ref&gt;&lt;ref name=CochraneNursHomeStop2013&gt;{{cite journal | vauthors = Hughes C, Tunney M, Bradley MC | title = Infection control strategies for preventing the transmission of meticillin-resistant Staphylococcus aureus (MRSA) in nursing homes for older people | journal = The Cochrane Database of Systematic Reviews | issue = 11 | article-number = CD006354 | date = November 2013 | volume = 2013 | pmid = 24254890 | pmc = 7000924 | doi = 10.1002/14651858.CD006354.pub4 }}&lt;/ref&gt;

===Prison inmates and military personnel===
Prisons and military barracks&lt;ref name = Gopal2017 /&gt; can be crowded and confined, and poor hygiene conditions may proliferate, thus putting inhabitants at increased risk of contracting MRSA.&lt;ref name=cmr /&gt; Cases of MRSA in such populations were first reported in the United States and later in Canada. The earliest reports were made by the [[Centers for Disease Control and Prevention]] in US state prisons. In the news media, hundreds of reports of MRSA outbreaks in prisons appeared between 2000 and 2008. For example, in February 2008, the [[Tulsa County, Oklahoma|Tulsa County]] jail in [[Oklahoma]] started treating an average of 12 ''S. aureus'' cases per month.&lt;ref&gt;{{cite web|url=http://www.purebio.com/about/article/48|title=PURE Bioscience|work=purebio.com|archive-url=https://web.archive.org/web/20090224131952/http://purebio.com/about/article/48|archive-date=2009-02-24}}&lt;/ref&gt;

=== Animals ===
[[Antibiotic use in livestock]] increases the risk that MRSA will develop among the livestock and other animals that may reside near them; strains [[MRSA ST398]] and [[CC398]] are transmissible to humans.&lt;ref name = Gopal2017&gt;{{cite journal | vauthors = Gopal S, Divya KC | title = Staphylococcus aureus prevalence from dairy cows in India act as potential risk for community-associated infections?: A review | journal = Veterinary World | volume = 10 | issue = 3 | pages = 311–318 | date = March 2017 | pmid = 28435193 | pmc = 5387658 | doi = 10.14202/vetworld.2017.311-318 }}&lt;/ref&gt;&lt;ref name = Mehn2014&gt;{{cite journal | vauthors = Mehndiratta PL, Bhalla P | title = Use of antibiotics in animal agriculture &amp; emergence of methicillin-resistant Staphylococcus aureus (MRSA) clones: need to assess the impact on public health | journal = The Indian Journal of Medical Research | volume = 140 | issue = 3 | pages = 339–44 | date = September 2014 | pmid = 25366200 | pmc = 4248379 }}&lt;/ref&gt; Generally, animals are asymptomatic.&lt;ref name =CochraneSurg2013 /&gt;

Domestic pets are susceptible to MRSA infection by transmission from their owners; conversely, MRSA-infected pets can also transmit MRSA to humans.&lt;ref&gt;{{cite journal | vauthors = Vitale CB, Gross TL, Weese JS | title = Methicillin-resistant Staphylococcus aureus in cat and owner | journal = Emerging Infectious Diseases | volume = 12 | issue = 12 | pages = 1998–2000 | date = December 2006 | pmid = 17354344 | pmc = 3291366 | doi = 10.3201/eid1212.060725 }} {{CDC}}&lt;/ref&gt;

=== Athletes ===
[[Changing room|Locker rooms]], [[gym]]s, and related athletic facilities offer potential sites for MRSA contamination and infection.&lt;ref&gt;{{cite journal | vauthors = Salgado CD, Farr BM, Calfee DP | title = Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors | journal = Clinical Infectious Diseases | volume = 36 | issue = 2 | pages = 131–9 | date = January 2003 | pmid = 12522744 | doi = 10.1086/345436 | doi-access = free }}&lt;/ref&gt; Athletes have been identified as a high-risk group.&lt;ref name = Gopal2017 /&gt; A study linked MRSA to the abrasions caused by [[artificial turf]].&lt;ref&gt;{{cite journal | vauthors = Kazakova SV, Hageman JC, Matava M, Srinivasan A, Phelan L, Garfinkel B, Boo T, McAllister S, Anderson J, Jensen B, Dodson D, Lonsway D, McDougal LK, Arduino M, Fraser VJ, Killgore G, Tenover FC, Cody S, Jernigan DB | title = A clone of methicillin-resistant Staphylococcus aureus among professional football players | journal = The New England Journal of Medicine | volume = 352 | issue = 5 | pages = 468–75 | date = February 2005 | pmid = 15689585 | doi = 10.1056/NEJMoa042859 | doi-access = free }}&lt;/ref&gt; Three studies by the Texas State Department of Health found the infection rate among football players was 16 times the national average. In October 2006, a high-school football player was temporarily paralyzed from MRSA-infected turf burns. His infection returned in January 2007 and required three surgeries to remove infected tissue and three weeks of hospital stay.&lt;ref name=epstein1&gt;{{cite news |url=https://www.bloomberg.com/apps/news?pid=newsarchive&amp;sid=alxhrJDn.cdc |title=Texas Football Succumbs to Virulent Staph Infection From Turf | vauthors = Epstein V |date=21 December 2007 |publisher=[[Bloomberg L.P.|Bloomberg]] |access-date=10 June 2010}}&lt;/ref&gt;

In 2013, [[Lawrence Tynes]], [[Carl Nicks (American football)|Carl Nicks]], and [[Johnthan Banks]] of the [[Tampa Bay Buccaneers]] were diagnosed with MRSA. Tynes and Nicks apparently did not contract the infection from each other, but whether Banks contracted it from either individual is unknown.&lt;ref&gt;{{cite web |url=https://www.espn.com/nfl/story/_/id/9808469/third-tampa-bay-buccaneers-player-tests-positive-mrsa-staph-infection |title=Third Tampa Bay Buccaneers player tests positive for MRSA staph infection |publisher=ESPN Internet Ventures |work=ESPN |date=11 October 2013 |access-date=11 October 2013 | vauthors = Yasinskas P }}&lt;/ref&gt; In 2015, [[Los Angeles Dodgers]] infielder [[Justin Turner]] was infected while the team visited the [[New York Mets]].&lt;ref&gt;{{cite news | vauthors = Hernandez D |url=http://www.latimes.com/sports/dodgers/dodgersnow/la-sp-dn-dodgers-justin-turner-nears-return-20150812-story.html|title=Dodgers' Justin Turner nears return from MRSA infection|work=[[Los Angeles Times]]|date=August 12, 2015|access-date=August 13, 2015}}&lt;/ref&gt; In October 2015, [[New York Giants]] tight end [[Daniel Fells]] was hospitalized with a serious MRSA infection.&lt;ref&gt;{{cite news | vauthors = Rappoport I |url=http://www.nfl.com/news/story/0ap3000000553694/article/mrsa-infection-leaves-giants-daniel-fells-in-dire-situation |archive-url=https://web.archive.org/web/20151011201636/http://www.nfl.com/news/story/0ap3000000553694/article/mrsa-infection-leaves-giants-daniel-fells-in-dire-situation |archive-date=October 11, 2015 |title=MRSA infection leaves Giants' Daniel Fells in dire situation |work=[[NFL.com]] |date=October 11, 2015 |access-date=October 12, 2015}}&lt;/ref&gt;

=== Children ===
MRSA is becoming a critical problem in children;&lt;ref&gt;{{cite journal | vauthors = Gray JW | title = MRSA: the problem reaches paediatrics | journal = Archives of Disease in Childhood | volume = 89 | issue = 4 | pages = 297–8 | date = April 2004 | pmid = 15033832 | pmc = 1719885 | doi = 10.1136/adc.2003.045534 }}&lt;/ref&gt; studies found 4.6% of patients in U.S. health-care facilities, (presumably) including hospital nurseries,&lt;ref&gt;{{cite journal | vauthors = Bratu S, Eramo A, Kopec R, Coughlin E, Ghitan M, Yost R, Chapnick EK, Landman D, Quale J | title = Community-associated methicillin-resistant Staphylococcus aureus in hospital nursery and maternity units | journal = Emerging Infectious Diseases | volume = 11 | issue = 6 | pages = 808–13 | date = June 2005 | pmid = 15963273 | pmc = 3367583 | doi = 10.3201/eid1106.040885 }}&lt;/ref&gt; were infected or colonized with MRSA.&lt;ref name=APIC&gt;{{cite web
|url= http://www.apic.org/Content/NavigationMenu/ResearchFoundation/NationalMRSAPrevalenceStudy/MRSA_Study_Results.htm
|title= National Prevalence Study of Methicillin-Resistant ''Staphylococcus aureus'' (MRSA) in U.S. Healthcare Facilities
|website= Association for Professionals in Infection Control &amp; Epidemiology
|date=June 25, 2007
|access-date= 2007-07-14
|archive-url= https://web.archive.org/web/20070907201425/http://www.apic.org/Content/NavigationMenu/ResearchFoundation/NationalMRSAPrevalenceStudy/MRSA_Study_Results.htm |archive-date=September 7, 2007}}&lt;/ref&gt; Children and adults who come in contact with day-care centers,&lt;ref name = Gopal2017 /&gt; playgrounds, locker rooms, camps, dormitories, classrooms and other school settings, and gyms and workout facilities are at higher risk of contracting MRSA. Parents should be especially cautious of children who participate in activities where sports equipment is shared, such as football helmets and uniforms.&lt;ref&gt;{{cite web |url=http://www.webmd.com/parenting/mrsa-and-staph-infections-in-children |title=Staph Infections and MRSA in Children: Prevention, Symptoms, and Treatment |work=webmd.com}}&lt;/ref&gt;

=== Intravenous drug users ===
Needle-required drugs have caused an increase of MRSA,&lt;ref&gt;{{cite journal | vauthors = Parikh MP, Octaria R, Kainer MA | title = Methicillin-Resistant Staphylococcus aureus Bloodstream Infections and Injection Drug Use, Tennessee, USA, 2015-2017 | language = en-us | journal = Emerging Infectious Diseases | volume = 26 | issue = 3 | pages = 446–453 | date = March 2020 | pmid = 32091385 | pmc = 7045815 | doi = 10.3201/eid2603.191408 | s2cid = 211098414 }}&lt;/ref&gt; with injection drug use (IDU) making up 24.1% (1,839 individuals) of Tennessee Hospital's Discharge System. The unsanitary methods of injection cause an access point for the MRSA to enter the bloodstream and begin infecting the host. Furthermore, with MRSA's high contagion rate,&lt;ref name=&quot;Loewen 512–520&quot;/&gt; a common risk factor is individuals who are in constant contact with someone who has injected drugs in the past year.

== Mechanism ==
[[Antimicrobial resistance]] is genetically based; resistance is mediated by the acquisition of extrachromosomal genetic elements containing genes that confer resistance to certain antibiotics. Examples of such elements include [[plasmid]]s, [[transposable element|transposable genetic elements]], and [[genomic islands]], which can be transferred between bacteria through [[horizontal gene transfer]].&lt;ref name=jenson1&gt;{{cite journal | vauthors = Jensen SO, Lyon BR | title = Genetics of antimicrobial resistance in Staphylococcus aureus | journal = Future Microbiology | volume = 4 | issue = 5 | pages = 565–82 | date = June 2009 | pmid = 19492967 | doi = 10.2217/fmb.09.30 }}&lt;/ref&gt; A defining characteristic of MRSA is its ability to thrive in the presence of [[penicillin]]-like antibiotics, which normally prevent bacterial growth by inhibiting the synthesis of [[cell wall]] material. This is due to a resistance gene, ''mecA'', which stops β-lactam antibiotics from inactivating the enzymes (transpeptidases) critical for cell wall synthesis.&lt;ref&gt;{{cite journal | vauthors = Chambers HF | title = Methicillin-resistant Staphylococcus aureus. Mechanisms of resistance and implications for treatment | journal = Postgraduate Medicine | volume = 109 | issue = 2 Suppl | pages = 43–50 | date = February 2001 | pmid = 19667557 | doi = 10.3810/pgm.02.2001.suppl12.65 | doi-broken-date = 12 July 2025 }}&lt;/ref&gt;

=== SCC''mec'' ===
Staphylococcal [[gene cassette|cassette chromosome]] ''mec'' ([[SCCmec|SCC''mec'']]) is a genomic island of unknown origin containing the antibiotic resistance gene ''mecA''.&lt;ref name=lowy1&gt;{{cite journal | vauthors = Lowy FD | title = Antimicrobial resistance: the example of Staphylococcus aureus | journal = The Journal of Clinical Investigation | volume = 111 | issue = 9 | pages = 1265–73 | date = May 2003 | pmid = 12727914 | pmc = 154455 | doi = 10.1172/JCI18535 }}&lt;/ref&gt;&lt;ref name=monaco1&gt;{{cite journal | vauthors = Pantosti A, Sanchini A, Monaco M | title = Mechanisms of antibiotic resistance in Staphylococcus aureus | journal = Future Microbiology | volume = 2 | issue = 3 | pages = 323–34 | date = June 2007 | pmid = 17661706 | doi = 10.2217/17460913.2.3.323 }}&lt;/ref&gt; SCC''mec'' contains additional genes beyond ''mecA'', including the [[cytolysin]] gene ''psm-mec'', which may suppress virulence in HA-acquired MRSA strains.&lt;ref&gt;{{cite journal | vauthors = Kaito C, Saito Y, Nagano G, Ikuo M, Omae Y, Hanada Y, Han X, Kuwahara-Arai K, Hishinuma T, Baba T, Ito T, Hiramatsu K, Sekimizu K | title = Transcription and translation products of the cytolysin gene psm-mec on the mobile genetic element SCCmec regulate Staphylococcus aureus virulence | journal = PLOS Pathogens | volume = 7 | issue = 2 | article-number = e1001267 | date = February 2011 | pmid = 21304931 | pmc = 3033363 | doi = 10.1371/journal.ppat.1001267 | veditors = Cheung A | doi-access = free }}&lt;/ref&gt; In addition, this locus encodes strain-dependent gene regulatory RNAs known as ''psm-mec''RNA.&lt;ref&gt;{{cite journal | vauthors = Cheung GY, Villaruz AE, Joo HS, Duong AC, Yeh AJ, Nguyen TH, Sturdevant DE, Queck SY, Otto M | title = Genome-wide analysis of the regulatory function mediated by the small regulatory psm-mec RNA of methicillin-resistant Staphylococcus aureus | journal = International Journal of Medical Microbiology | volume = 304 | issue = 5–6 | pages = 637–44 | date = July 2014 | pmid = 24877726 | pmc = 4087065 | doi = 10.1016/j.ijmm.2014.04.008 }}&lt;/ref&gt; SCC''mec'' also contains ''ccrA'' and ''ccrB''; both genes encode recombinases that mediate the site-specific integration and excision of the SCC''mec'' element from the ''S. aureus'' chromosome.&lt;ref name=&quot;lowy1&quot; /&gt;&lt;ref name=&quot;monaco1&quot; /&gt; Currently, six unique SCC''mec'' types ranging in size from 21 to 67 kb have been identified;&lt;ref name=&quot;lowy1&quot; /&gt; they are designated types I–VI and are distinguished by variation in ''mec'' and ''ccr'' gene complexes.&lt;ref name=&quot;jenson1&quot; /&gt; Owing to the size of the SCC''mec'' element and the constraints of horizontal gene transfer, a minimum of five clones are thought to be responsible for the spread of MRSA infections, with clonal complex (CC) 8 most prevalent.&lt;ref name=&quot;lowy1&quot; /&gt;&lt;ref&gt;{{cite journal | vauthors = Enright MC, Robinson DA, Randle G, Feil EJ, Grundmann H, Spratt BG | title = The evolutionary history of methicillin-resistant Staphylococcus aureus (MRSA) | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 11 | pages = 7687–92 | date = May 2002 | pmid = 12032344 | pmc = 124322 | doi = 10.1073/pnas.122108599 | bibcode = 2002PNAS...99.7687E | doi-access = free }}&lt;/ref&gt; SCC''mec'' is thought to have originated in the closely related ''[[Staphylococcus sciuri]]'' species and transferred horizontally to ''S. aureus.''&lt;ref&gt;{{cite journal | vauthors = Wu SW, de Lencastre H, Tomasz A | title = Recruitment of the mecA gene homologue of Staphylococcus sciuri into a resistance determinant and expression of the resistant phenotype in Staphylococcus aureus | journal = Journal of Bacteriology | volume = 183 | issue = 8 | pages = 2417–24 | date = April 2001 | pmid = 11274099 | pmc = 95156 | doi = 10.1128/JB.183.8.2417-2424.2001 }}&lt;/ref&gt;

Different SCC''mec'' genotypes confer different microbiological characteristics, such as different antimicrobial resistance rates.&lt;ref name=kuo1&gt;{{cite journal | vauthors = Kuo SC, Chiang MC, Lee WS, Chen LY, Wu HS, Yu KW, Fung CP, Wang FD | title = Comparison of microbiological and clinical characteristics based on SCCmec typing in patients with community-onset meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia | journal = International Journal of Antimicrobial Agents | volume = 39 | issue = 1 | pages = 22–6 | date = January 2012 | pmid = 21982834 | doi = 10.1016/j.ijantimicag.2011.08.014 | url = http://ir.nhri.org.tw/bitstream/3990099045/6059/1/SCP80053518786.pdf }}&lt;/ref&gt; Different genotypes are also associated with different types of infections. Types I–III SCC''mec'' are large elements that typically contain additional resistance genes and are characteristically isolated from HA-MRSA strains.&lt;ref name=monaco1 /&gt;&lt;ref name=kuo1 /&gt; Conversely, CA-MRSA is associated with types IV and V, which are smaller and lack resistance genes other than ''mecA''.&lt;ref name=monaco1 /&gt;&lt;ref name=kuo1 /&gt;

These distinctions were thoroughly investigated by Collins et al. in 2001 and can be explained by the fitness differences associated with the carriage of a large or small SCC''mec'' plasmid. Carriage of large plasmids, such as SCC''mec''I–III, is costly to the bacteria, resulting in a compensatory decrease in [[virulence]] expression.&lt;ref name=&quot;:0&quot;&gt;{{cite journal | vauthors = Collins J, Rudkin J, Recker M, Pozzi C, O'Gara JP, Massey RC | s2cid = 38231565 | title = Offsetting virulence and antibiotic resistance costs by MRSA | journal = The ISME Journal | volume = 4 | issue = 4 | pages = 577–84 | date = April 2010 | pmid = 20072161 | doi = 10.1038/ismej.2009.151 | bibcode = 2010ISMEJ...4..577C | doi-access = free }}&lt;/ref&gt; MRSA can thrive in hospital settings with increased antibiotic resistance but decreased virulence – HA-MRSA targets immunocompromised, hospitalized hosts, thus a decrease in virulence is not maladaptive.&lt;ref name=&quot;:0&quot; /&gt; In contrast, CA-MRSA tends to carry lower-fitness cost SCC''mec'' elements to offset the increased virulence and toxicity expression required to infect healthy hosts.&lt;ref name=&quot;:0&quot; /&gt;

=== ''mecA'' ===
[[MecA (gene)|''mecA'']] is a [[biomarker]] gene responsible for resistance to methicillin and other β-lactam antibiotics. After the acquisition of ''mecA'', the gene must be integrated and localized in the ''S. aureus'' chromosome.&lt;ref name=lowy1 /&gt; ''mecA'' encodes penicillin-binding protein 2a (PBP2a), which differs from other penicillin-binding proteins as its active site does not bind methicillin or other β-lactam antibiotics.&lt;ref name=lowy1 /&gt; As such, PBP2a can continue to catalyze the transpeptidation reaction required for [[peptidoglycan]] cross-linking, enabling cell wall synthesis even in the presence of antibiotics. As a consequence of the inability of PBP2a to interact with β-lactam moieties, acquisition of ''mecA'' confers resistance to almost all β-lactam antibiotics in addition to methicillin.&lt;ref name=lowy1 /&gt;&lt;ref&gt;Sahebnasagh R, Saderi H, Owlia P. Detection of methicillin-resistant Staphylococcus aureus strains from clinical samples in Tehran by detection of the mecA and nuc genes. The First Iranian International Congress of Medical Bacteriology; 4–7 September; Tabriz, Iran. 2011. 195 pp.&lt;/ref&gt;

''mecA'' is under the control of two [[regulatory genes]], ''mecI'' and ''mecR1''. MecI is usually bound to the ''mecA'' promoter and functions as a [[repressor]].&lt;ref name=jenson1 /&gt;&lt;ref name=monaco1 /&gt; In the presence of a β-lactam antibiotic, MecR1 initiates a [[signal transduction cascade]] that leads to transcriptional activation of ''mecA''.&lt;ref name=jenson1 /&gt;&lt;ref name=monaco1 /&gt; This is achieved by MecR1-mediated cleavage of MecI, which alleviates MecI repression.&lt;ref name=jenson1 /&gt; ''mecA'' is further controlled by two co-repressors, ''blaI'' and ''blaR1''. ''blaI'' and ''blaR1'' are homologous to ''mecI'' and ''mecR1'', respectively, and normally function as regulators of ''blaZ'', which is responsible for penicillin resistance.&lt;ref name=lowy1 /&gt;&lt;ref name=&quot;berger-bachi&quot;&gt;{{cite journal | vauthors = Berger-Bächi B | s2cid = 40019841 | title = Genetic basis of methicillin resistance in Staphylococcus aureus | journal = Cellular and Molecular Life Sciences | volume = 56 | issue = 9–10 | pages = 764–70 | date = November 1999 | pmid = 11212336 | doi = 10.1007/s000180050023 | url = http://link.springer.de/link/service/journals/00018/bibs/90569-10/90560764.htm | archive-url = https://archive.today/20130212050521/http://link.springer.de/link/service/journals/00018/bibs/90569-10/90560764.htm | archive-date = 2013-02-12 | pmc = 11146767 }}&lt;/ref&gt; The DNA sequences bound by ''mecI'' and ''blaI'' are identical;&lt;ref name=lowy1 /&gt; therefore, ''blaI'' can also bind the ''mecA'' operator to repress transcription of ''mecA''.&lt;ref name=&quot;berger-bachi&quot; /&gt;

=== Arginine catabolic mobile element ===
The [[arginine catabolic mobile element]] (ACME) is a virulence factor present in many MRSA strains but not prevalent in MSSA.&lt;ref name= PMID17409207&gt;{{cite journal | vauthors = Goering RV, McDougal LK, Fosheim GE, Bonnstetter KK, Wolter DJ, Tenover FC | title = Epidemiologic distribution of the arginine catabolic mobile element among selected methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolates | journal = Journal of Clinical Microbiology | volume = 45 | issue = 6 | pages = 1981–1984 | date = June 2007 | pmid = 17409207 | pmc = 1933090 | doi = 10.1128/JCM.00273-07 }}&lt;/ref&gt; SpeG-positive ACME compensates for the [[polyamine]] hypersensitivity of ''S. aureus'' and facilitates stable skin colonization, wound infection, and person-to-person transmission.&lt;ref&gt;{{cite journal | vauthors = Joshi GS, Spontak JS, Klapper DG, Richardson AR | title = Arginine catabolic mobile element encoded speG abrogates the unique hypersensitivity of Staphylococcus aureus to exogenous polyamines | journal = Molecular Microbiology | volume = 82 | issue = 1 | pages = 9–20 | date = October 2011 | pmid = 21902734 | pmc = 3183340 | doi = 10.1111/j.1365-2958.2011.07809.x | publisher = Wiley }}&lt;/ref&gt;

=== Strains ===
[[File:mecA Resistance.svg|thumb|right|Diagram depicting antibiotic resistance through alteration of the antibiotic's target site, modeled after MRSA's resistance to penicillin. Beta-lactam antibiotics permanently inactivate [[penicillin binding protein|PBP enzymes]], which are essential for cell wall synthesis and thus for bacterial life, by permanently binding to their active sites. Some forms of MRSA, however, express a different PBP that will not allow the antibiotic into its active site.]]
Acquisition of SCC''mec'' in methicillin-sensitive ''S. aureus'' (MSSA) gives rise to several genetically different MRSA lineages. These genetic variations within different MRSA strains possibly explain the variability in virulence and associated MRSA infections.&lt;ref name=GordonLowy2008&gt;{{cite journal | vauthors = Gordon RJ, Lowy FD | title = Pathogenesis of methicillin-resistant Staphylococcus aureus infection | journal = Clinical Infectious Diseases | volume = 46 | issue = Suppl 5 | pages = S350–9 | date = June 2008 | pmid = 18462090 | pmc = 2474459 | doi = 10.1086/533591 }}&lt;/ref&gt; The first MRSA strain, ST250 MRSA-1, originated from SCC''mec'' and ST250-MSSA integration.&lt;ref name=GordonLowy2008 /&gt; Historically, major MRSA clones ST2470-MRSA-I, ST239-MRSA-III, ST5-MRSA-II, and ST5-MRSA-IV were responsible for causing hospital-acquired MRSA (HA-MRSA) infections.&lt;ref name=GordonLowy2008 /&gt; ST239-MRSA-III, known as the Brazilian clone, was highly transmissible compared to others and distributed in Argentina, Czech Republic, and Portugal.&lt;ref name=GordonLowy2008 /&gt;

In the UK, the most common strains of MRSA are EMRSA15 and EMRSA16.&lt;ref name=&quot;JAntimicrobChemother2001-Johnson&quot;&gt;{{cite journal | vauthors = Johnson AP, Aucken HM, Cavendish S, Ganner M, Wale MC, Warner M, Livermore DM, Cookson BD | title = Dominance of EMRSA-15 and -16 among MRSA causing nosocomial bacteraemia in the UK: analysis of isolates from the European Antimicrobial Resistance Surveillance System (EARSS) | journal = The Journal of Antimicrobial Chemotherapy | volume = 48 | issue = 1 | pages = 143–4 | date = July 2001 | pmid = 11418528 | doi = 10.1093/jac/48.1.143 | doi-access = free }}&lt;/ref&gt; EMRSA16 is identical to the [[MLST|ST]]36:USA200 strain, which circulates in the United States, and to carry the SCC''mec'' type II, [[enterotoxin]] A and [[toxic shock syndrome]] toxin 1 genes.&lt;ref name=diep2006 /&gt; Under the new international typing system, this strain is now called MRSA252. EMRSA 15 is also found to be one of the common MRSA strains in Asia. Other common strains include ST5:USA100 and EMRSA 1.&lt;ref name=&quot;StefaniChung2012&quot;&gt;{{cite journal | vauthors = Stefani S, Chung DR, Lindsay JA, Friedrich AW, Kearns AM, Westh H, Mackenzie FM | title = Meticillin-resistant Staphylococcus aureus (MRSA): global epidemiology and harmonisation of typing methods | journal = International Journal of Antimicrobial Agents | volume = 39 | issue = 4 | pages = 273–82 | date = April 2012 | pmid = 22230333 | doi = 10.1016/j.ijantimicag.2011.09.030 }}&lt;/ref&gt; These strains are genetic characteristics of HA-MRSA.&lt;ref name=calfee2011&gt;{{cite journal | vauthors = Calfee DP | title = The epidemiology, treatment, and prevention of transmission of methicillin-resistant Staphylococcus aureus | journal = Journal of Infusion Nursing | volume = 34 | issue = 6 | pages = 359–64 | year = 2011 | pmid = 22101629 | doi = 10.1097/NAN.0b013e31823061d6 | s2cid = 11490852 }}&lt;/ref&gt;

Community-acquired MRSA (CA-MRSA) strains emerged in late 1990 to 2000, infecting healthy people who had not been in contact with healthcare facilities.&lt;ref name=calfee2011 /&gt; Researchers suggest that CA-MRSA did not evolve from HA-MRSA.&lt;ref name=calfee2011 /&gt; This is further proven by molecular typing of CA-MRSA strains&lt;ref name=daum2007&gt;{{cite journal | vauthors = Daum RS | title = Clinical practice. Skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus | journal = The New England Journal of Medicine | volume = 357 | issue = 4 | pages = 380–90 | date = July 2007 | pmid = 17652653 | doi = 10.1056/NEJMcp070747 }}&lt;/ref&gt; and genome comparison between CA-MRSA and HA-MRSA, which indicate that novel MRSA strains integrated SCC''mec'' into MSSA separately on its own.&lt;ref name=calfee2011 /&gt; By mid-2000, CA-MRSA was introduced into healthcare systems and distinguishing CA-MRSA from HA-MRSA became a difficult process.&lt;ref name=calfee2011 /&gt; Community-acquired MRSA is more easily treated and more virulent than hospital-acquired MRSA (HA-MRSA).&lt;ref name=calfee2011 /&gt; The genetic mechanism for the enhanced virulence in CA-MRSA remains an active area of research. The [[Panton–Valentine leukocidin]] (PVL) genes are of particular interest because they are a unique feature of CA-MRSA.&lt;ref name=GordonLowy2008 /&gt;

In the United States, most cases of CA-MRSA are caused by a CC8 strain designated [[ST8:USA300]], which carries SCC''mec'' type IV, [[Panton–Valentine leukocidin]], [[phenol-soluble modulin|PSM-alpha]] and [[enterotoxin]]s Q and K,&lt;ref name=diep2006&gt;{{cite journal | vauthors = Diep BA, Carleton HA, Chang RF, Sensabaugh GF, Perdreau-Remington F | title = Roles of 34 virulence genes in the evolution of hospital- and community-associated strains of methicillin-resistant Staphylococcus aureus | journal = The Journal of Infectious Diseases | volume = 193 | issue = 11 | pages = 1495–503 | date = June 2006 | pmid = 16652276 | doi = 10.1086/503777 | doi-access = free }}&lt;/ref&gt; and [[ST1:USA400]].&lt;ref&gt;{{cite journal | vauthors = Wang R, Braughton KR, Kretschmer D, Bach TH, Queck SY, Li M, Kennedy AD, Dorward DW, Klebanoff SJ, Peschel A, DeLeo FR, Otto M | s2cid = 8465052 | title = Identification of novel cytolytic peptides as key virulence determinants for community-associated MRSA | journal = Nature Medicine | volume = 13 | issue = 12 | pages = 1510–4 | date = December 2007 | pmid = 17994102 | doi = 10.1038/nm1656 }}&lt;/ref&gt; The ST8:USA300 strain results in skin infections, [[necrotizing fasciitis]], and toxic shock syndrome, whereas the ST1:USA400 strain results in necrotizing pneumonia and pulmonary sepsis.&lt;ref name=GordonLowy2008 /&gt; Other community-acquired strains of MRSA are ST8:USA500 and ST59:USA1000. In many nations of the world, MRSA strains with different genetic background types have come to predominate among CA-MRSA strains; USA300 easily tops the list in the U.S. and is becoming more common in Canada after its first appearance there in 2004. For example, in Australia, ST93 strains are common, while in continental Europe ST80 strains, which carry SCC''mec'' type IV, predominate.&lt;ref&gt;{{cite journal | vauthors = Tristan A, Bes M, Meugnier H, Lina G, Bozdogan B, Courvalin P, Reverdy ME, Enright MC, Vandenesch F, Etienne J | title = Global distribution of Panton-Valentine leukocidin--positive methicillin-resistant Staphylococcus aureus, 2006 | journal = Emerging Infectious Diseases | volume = 13 | issue = 4 | pages = 594–600 | date = April 2007 | pmid = 17553275 | pmc = 2725977 | doi = 10.3201/eid1304.061316 }}&lt;/ref&gt;&lt;ref name=&quot;GouldDavid2012&quot;&gt;{{cite journal |vauthors=Gould IM, David MZ, Esposito S, Garau J, Lina G, Mazzei T, Peters G|title=New insights into meticillin-resistant Staphylococcus aureus (MRSA) pathogenesis, treatment and resistance|journal=International Journal of Antimicrobial Agents|volume=39|issue=2|pages=96–104|date=February 2012|pmid=22196394|doi=10.1016/j.ijantimicag.2011.09.028|url=https://www.sciencedirect.com/science/article/pii/S0924857911004596}}&lt;/ref&gt; In Taiwan, ST59 strains, some of which are resistant to many non-beta-lactam antibiotics, have arisen as common causes of skin and soft tissue infections in the community. In a remote region of Alaska, unlike most of the continental U.S., USA300 was found only rarely in a study of MRSA strains from outbreaks in 1996 and 2000, as well as in surveillance from 2004 to 2006.&lt;ref name=&quot;pmid18976551&quot;&gt;{{cite journal | vauthors = David MZ, Rudolph KM, Hennessy TW, Boyle-Vavra S, Daum RS | title = Molecular epidemiology of methicillin-resistant Staphylococcus aureus, rural southwestern Alaska | journal = Emerging Infectious Diseases | volume = 14 | issue = 11 | pages = 1693–9 | date = November 2008 | pmid = 18976551 | pmc = 2630737 | doi = 10.3201/eid1411.080381 }}&lt;/ref&gt;

A MRSA strain, [[CC398]], is found in [[intensive animal farming|intensively reared]] production animals (primarily pigs, but also cattle and poultry), where it can be transmitted to humans as LA-MRSA (livestock-associated MRSA).&lt;ref name=&quot;StefaniChung2012&quot; /&gt;&lt;ref&gt;{{cite journal| author = Panel on Biological Hazards|title=Joint scientific report of ECDC, EFSA and EMEA on meticillin resistant Staphylococcus aureus (MRSA) in livestock, companion animals and food.|journal=EFSA Journal|volume=7|issue=6|date=16 June 2009|doi=10.2903/j.efsa.2009.301r|doi-access=free}}&lt;/ref&gt;&lt;ref name=&quot;GravelandDuim2011&quot;&gt;{{cite journal | vauthors = Graveland H, Duim B, van Duijkeren E, Heederik D, Wagenaar JA | title = Livestock-associated methicillin-resistant Staphylococcus aureus in animals and humans | journal = International Journal of Medical Microbiology | volume = 301 | issue = 8 | pages = 630–4 | date = December 2011 | pmid = 21983338 | doi = 10.1016/j.ijmm.2011.09.004 | hdl = 1874/407042 | s2cid = 381926 | hdl-access = free }}&lt;/ref&gt;

== Diagnosis ==
[[File:MRSA on a selective choromogenic media plate.jpg|thumb|right|A selective and differential chromogenic medium for the qualitative direct detection of MRSA]]
[[File:MRSA on MHA media resistant to oxacillin antibiotic strip.jpg|thumb|right|MRSA resistance to oxacillin being tested. The top ''S. aureus'' isolate is a control that is not resistant to oxacillin; the other three isolates are MRSA-positive.]]
[[File:Muller Hinton agar with MRSA.jpg|thumb|[[Mueller–Hinton agar]] showing MRSA resistant to an oxacillin disk]]
Diagnostic microbiology laboratories and reference laboratories are key for identifying outbreaks of MRSA. Normally, a bacterium must be cultured from blood, urine, [[sputum]], or other body-fluid samples, and in sufficient quantities to perform confirmatory tests early on. Still, because no quick and easy method exists to diagnose MRSA, initial treatment of the infection is often based upon &quot;strong suspicion&quot; and techniques by the treating physician; these include [[quantitative PCR]] procedures, which are employed in clinical laboratories for quickly detecting and identifying MRSA strains.&lt;ref name= FrancoisP&gt;{{cite book |chapter-url=http://www.horizonpress.com/staph|vauthors=Francois P, Schrenzel J|year=2008|chapter=Rapid Diagnosis and Typing of ''Staphylococcus aureus''|title=Staphylococcus: Molecular Genetics|publisher=Caister Academic Press |isbn=978-1-904455-29-5}}&lt;/ref&gt;&lt;ref name=Mackay&gt;{{cite book | veditors = Mackay IM |title= Real-Time PCR in Microbiology: From Diagnosis to Characterization |publisher= Caister Academic Press |year= 2007 |url=http://www.horizonpress.com/rtmic |isbn=978-1-904455-18-9}}&lt;/ref&gt;

Another common laboratory test is a rapid latex [[agglutination (biology)|agglutination]] test that detects the PBP2a protein. PBP2a is a variant [[penicillin-binding protein]] that imparts the ability of ''S. aureus'' to be resistant to oxacillin.&lt;ref name=Hardy&gt;{{cite web |title=MRSA latex test for PBP2 | vauthors = Seiken D |url=http://www.hardydiagnostics.com/catalog2/hugo/MRSALatexTest.htm |access-date=2009-01-24 |archive-date=2009-03-10 |archive-url=https://web.archive.org/web/20090310034548/http://www.hardydiagnostics.com/catalog2/hugo/MRSALatexTest.htm }}&lt;/ref&gt;

=== Microbiology ===
Like all ''S. aureus'' (also abbreviated SA at times), methicillin-resistant ''S. aureus'' is a gram-positive, spherical ([[coccus]]) [[bacterium]] about 1 [[micron]] in [[diameter]]. It does not form [[Endospore|spores]] and it is not [[Motility|motile]]. It is frequently found in grape-like clusters or chains.&lt;ref name=Murray&gt;{{cite book | vauthors = Murray P | title = Manual of clinical microbiology | publisher = [[ASM Press]] | location = Washington, D.C. | year = 2007 | isbn = 978-1-55581-371-0}}&lt;/ref&gt;{{rp|390}} Unlike methicillin-susceptible ''S. aureus'' (MSSA), MRSA is slow-growing on a variety of media and has been found to exist in mixed colonies of MSSA. The ''mecA'' gene, which confers resistance to several antibiotics, is always present in MRSA and usually absent in MSSA; however, in some instances, the ''mecA'' gene is present in MSSA but is not [[gene expression|expressed]]. [[Polymerase chain reaction]] (PCR) testing is the most precise method for identifying MRSA strains. Specialized culture media have been developed to better differentiate between MSSA and MRSA, and, in some cases, such media can be used to identify specific strains that are resistant to different antibiotics.&lt;ref name=Murray /&gt;{{rp|402}}

Other strains of ''S. aureus'' have emerged that are resistant to [[oxacillin]], clindamycin, teicoplanin, and [[erythromycin]]. These resistant strains may or may not possess the ''mecA'' gene. ''S. aureus'' has also developed resistance to [[vancomycin]] (VRSA). One strain is only partially susceptible to vancomycin and is called vancomycin-intermediate ''S. aureus'' (VISA). GISA, a strain of resistant'' S. aureus'', is glycopeptide-intermediate ''S. aureus'' and is less susceptible to vancomycin and teicoplanin. Resistance to antibiotics in ''S. aureus'' can be quantified by determining the amount of the antibiotic that must be used to inhibit growth. If ''S. aureus'' is inhibited at a concentration of vancomycin less than or equal to 4 μg/ml, it is said to be susceptible. If a concentration greater than 32 μg/ml is necessary to inhibit growth, it is said to be resistant.&lt;!--note that MRSA can be resistant to vancomycin as well as can VRSA--&gt;&lt;ref name=Winn&gt;{{cite book | vauthors = Winn W | title = Koneman's color atlas and textbook of diagnostic microbiology | publisher = Lippincott Williams &amp; Wilkins | location = Philadelphia | year = 2006 | isbn = 978-0-7817-3014-3 }}&lt;/ref&gt;{{rp|637}}

== Prevention ==
=== Screening ===
In health-care settings, isolating those with MRSA from those without the infection is one method to prevent transmission. Rapid culture and sensitivity testing and molecular testing identify carriers and reduce infection rates.&lt;ref&gt;{{cite journal | vauthors = Tacconelli E, De Angelis G, de Waure C, Cataldo MA, La Torre G, Cauda R | title = Rapid screening tests for meticillin-resistant Staphylococcus aureus at hospital admission: systematic review and meta-analysis | journal = The Lancet. Infectious Diseases | volume = 9 | issue = 9 | pages = 546–54 | date = September 2009 | pmid = 19695491 | doi = 10.1016/S1473-3099(09)70150-1 }}&lt;/ref&gt; It is especially important to test patients in these settings since 2% of people are [[Asymptomatic carrier|carriers]] of MRSA, even though in many of these cases the bacteria reside in the nostril and the patient will not present any symptoms.&lt;ref&gt;Healthcare Settings. (2019, February 28). Retrieved March 19, 2021, from https://www.cdc.gov/mrsa/healthcare/index.html&lt;/ref&gt;

MRSA can be identified by swabbing the nostrils and isolating the bacteria found there. Combined with extra sanitary measures for those in contact with infected people, swab screening people admitted to hospitals is effective in minimizing the spread of MRSA in hospitals in the United States, [[Denmark]], [[Finland]], and the [[Netherlands]].&lt;ref&gt;{{cite web |url=http://www.tufts.edu/med/apua/Patients/ridbooklet.pdf |title=Unnecessary Deaths: The Human and Financial Costs of Hospital Infections |access-date=2007-08-05 |edition=2nd| vauthors = McCaughey B|archive-url= https://web.archive.org/web/20070711030535/http://www.tufts.edu/med/apua/Patients/ridbooklet.pdf |archive-date= July 11, 2007}}&lt;/ref&gt;

=== Handwashing ===
The [[Centers for Disease Control and Prevention]] offers suggestions for preventing the contraction and spread of MRSA infection, which apply to those in community settings, including incarcerated populations, childcare center employees, and athletes. To prevent the spread of MRSA, the recommendations are to [[handwashing|wash hands]] thoroughly and regularly using soap and water or an alcohol-based sanitizer. Additional recommendations are to keep wounds clean and covered, avoid contact with other people's wounds, avoid sharing personal items such as razors or towels, shower after exercising at athletic facilities, and shower before using swimming pools or whirlpools.&lt;ref&gt;{{cite web |title= Personal Prevention of MRSA Skin Infections |publisher= CDC |access-date = 25 May 2017 |date= 9 August 2010 |url= https://www.cdc.gov/infectioncontrol/guidelines/mdro/index.html}}{{CDC}}&lt;/ref&gt;

=== Isolation ===
Excluding [[medical facility|medical facilities]], current US guidance does not require workers with MRSA infections to be routinely excluded from the general workplace.&lt;ref name=NIOSH_MRSA&gt;{{cite web |url= https://www.cdc.gov/niosh/topics/mrsa/ |title=NIOSH MRSA and the Workplace |access-date=2017-05-25|publisher=United States National Institute for Occupational Safety and Health}}&lt;/ref&gt; The [[National Institutes of Health]] recommend that those with wound drainage that cannot be covered and contained with a clean, dry bandage and those who cannot maintain good hygiene practices be reassigned,&lt;ref name=NIOSH_MRSA /&gt; and patients with wound drainage should also automatically be put on &quot;[[Transmission-based precaution|Contact Precaution]],&quot; regardless of whether or not they have a known infection.&lt;ref name=&quot;cdc.gov&quot;&gt;Strategies to Prevent Hospital-onset Staphylococcus aureus Bloodstream Infections in Acute Care Facilities. (2019, December 16). Retrieved March 19, 2021, from https://www.cdc.gov/hai/prevent/staph-prevention-strategies.html#anchor_1565005744&lt;/ref&gt; Workers with active infections are excluded from activities where skin-to-skin contact is likely to occur.&lt;ref name=CDC1998&gt;{{cite web |url=https://www.cdc.gov/ncidod/dhqp/gl_hcpersonnel.html|title=Guidelines for Infection Control in Health Care Personnel, 1998|access-date=December 18, 2007|publisher=[[Centers for Disease Control and Prevention]]|year=1998|author=CDC}}&lt;/ref&gt; To prevent the spread of [[staphylococci]] or MRSA in the workplace, employers are encouraged to make available adequate facilities that support good hygiene. In addition, surface and equipment sanitizing should conform to [[United States Environmental Protection Agency|Environmental Protection Agency]]-registered disinfectants.&lt;ref name=&quot;NIOSH_MRSA&quot; /&gt; In hospital settings, contact isolation can be stopped after one to three cultures come back negative.&lt;ref name=Ban2018&gt;{{cite journal | vauthors = Banach DB, Bearman G, Barnden M, Hanrahan JA, Leekha S, Morgan DJ, Murthy R, Munoz-Price LS, Sullivan KV, Popovich KJ, Wiemken TL | title = Duration of Contact Precautions for Acute-Care Settings | journal = Infection Control and Hospital Epidemiology | volume = 39 | issue = 2 | pages = 127–144 | date = February 2018 | pmid = 29321078 | doi = 10.1017/ice.2017.245 | doi-access = free }}&lt;/ref&gt; Before the patient is cleared from isolation, it is advised that there is dedicated patient-care or single-use equipment for that particular patient. If this is not possible, the equipment must be properly disinfected before it is used on another patient.&lt;ref name=&quot;cdc.gov&quot;/&gt;

To prevent the spread of MRSA in the home, health departments recommend laundering materials that have come into contact with infected persons separately and with a dilute bleach solution; to reduce the bacterial load in one's nose and skin; and to clean and disinfect those things in the house that people regularly touch, such as sinks, tubs, kitchen counters, cell phones, light switches, doorknobs, phones, toilets, and computer keyboards.&lt;ref name=tpchd /&gt;

=== Restricting antibiotic use ===
[[Glycopeptide antibiotic|Glycopeptides]], [[cephalosporin]]s, and in particular, [[Quinolone antibiotic|fluoroquinolones]] are associated with an increased risk of colonisation of MRSA. Reducing the use of antibiotic classes that promote MRSA colonisation, especially fluoroquinolones, is recommended in current guidelines.&lt;ref name=tacconelli2008 /&gt;&lt;ref name=muto2003&gt;{{cite journal | vauthors = Muto CA, Jernigan JA, Ostrowsky BE, Richet HM, Jarvis WR, Boyce JM, Farr BM | title = SHEA guideline for preventing nosocomial transmission of multidrug-resistant strains of Staphylococcus aureus and enterococcus | journal = Infection Control and Hospital Epidemiology | volume = 24 | issue = 5 | pages = 362–86 | date = May 2003 | pmid = 12785411 | doi = 10.1086/502213 | citeseerx = 10.1.1.575.8929 | s2cid = 19544705 }}&lt;/ref&gt;

=== Public health considerations ===
Mathematical models describe one way in which a loss of infection control can occur after measures for screening and isolation seem to be effective for years, as happened in the UK. In the &quot;search and destroy&quot; strategy that was employed by all UK hospitals until the mid-1990s, all hospitalized people with MRSA were immediately isolated, and all staff were screened for MRSA and were prevented from working until they had completed a course of eradication therapy that was proven to work. Loss of control occurs because colonised people are discharged back into the community and then readmitted; when the number of colonised people in the community reaches a certain threshold, the &quot;search and destroy&quot; strategy is overwhelmed.&lt;ref&gt;{{cite journal | vauthors = Cooper BS, Medley GF, Stone SP, Kibbler CC, Cookson BD, Roberts JA, Duckworth G, Lai R, Ebrahim S | title = Methicillin-resistant Staphylococcus aureus in hospitals and the community: stealth dynamics and control catastrophes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 101 | issue = 27 | pages = 10223–8 | date = July 2004 | pmid = 15220470 | pmc = 454191 | doi = 10.1073/pnas.0401324101 | bibcode = 2004PNAS..10110223C | doi-access = free }}&lt;/ref&gt; One of the few countries not to have been overwhelmed by MRSA is the Netherlands: an important part of the success of the Dutch strategy may have been to attempt eradication of carriage upon discharge from hospital.&lt;ref name=bootsma2006&gt;{{cite journal | vauthors = Bootsma MC, Diekmann O, Bonten MJ | title = Controlling methicillin-resistant Staphylococcus aureus: quantifying the effects of interventions and rapid diagnostic testing | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 14 | pages = 5620–5 | date = April 2006 | pmid = 16565219 | pmc = 1459403 | doi = 10.1073/pnas.0510077103 | bibcode = 2006PNAS..103.5620B | doi-access = free }}&lt;/ref&gt;

=== Decolonization ===
{{Main|Decolonization (medicine)}}
As of 2013, no randomized clinical trials had been conducted to understand how to treat nonsurgical wounds that had been colonized, but not infected, with MRSA,&lt;ref name=CochraneNonSurg2013 /&gt; and insufficient studies had been conducted to understand how to treat surgical wounds that had been colonized with MRSA.&lt;ref name = CochraneSurg2013 /&gt; As of 2013, whether strategies to eradicate MRSA colonization of people in nursing homes reduced infection rates was not known.&lt;ref name=CochraneNursHomeStop2013 /&gt;

Care should be taken when trying to drain boils, as disruption of surrounding tissue can lead to larger infections, including [[sepsis]] and [[bacteremia|bacterial infections of the bloodstream]].&lt;ref name=NIH&gt;{{cite web |title=MRSA (Methicillin-Resistant Staphylococcus aureus) |url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0004520/|publisher=[[US National Institutes of Health]] |work=[[National Library of Medicine]] | archive-url=https://web.archive.org/web/20110204185926/https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0004520/ |access-date=20 November 2011|archive-date=2011-02-04 }}&lt;/ref&gt; [[Mupirocin]] 2% ointment can be effective at reducing the size of lesions. A secondary covering of clothing is preferred.&lt;ref name=tpchd&gt;{{cite web|title=Living With MRSA|url=http://www.tpchd.org/files/library/2357adf2a147d1aa.pdf|publisher=Group Health Cooperative/Tacoma-Pierce County Health Dept./Washington State Dept. of Health|access-date=20 November 2011|archive-date=27 October 2011|archive-url=https://web.archive.org/web/20111027062639/http://www.tpchd.org/files/library/2357adf2a147d1aa.pdf}}&lt;/ref&gt; As shown in an animal study with diabetic mice, the topical application of a mixture of sugar (70%) and 3% povidone-iodine paste is an effective agent for the treatment of diabetic ulcers with MRSA infection.&lt;ref&gt;{{cite journal | vauthors = Shi CM, Nakao H, Yamazaki M, Tsuboi R, Ogawa H | s2cid = 28807435 | title = Mixture of sugar and povidone-iodine stimulates healing of MRSA-infected skin ulcers on db/db mice | journal = Archives of Dermatological Research | volume = 299 | issue = 9 | pages = 449–56 | date = November 2007 | pmid = 17680256 | doi = 10.1007/s00403-007-0776-3 }}&lt;/ref&gt;

=== Agriculture ===
{{See also|Antibiotic use in livestock}}
The [[World Health Organization]] advocates regulations on the use of antibiotics in animal feed to prevent the emergence of drug-resistant strains of MRSA.&lt;ref name = Mehn2014 /&gt; MRSA is established in animals and birds.&lt;ref name = Gopal2017 /&gt;

== Treatment ==
=== Antibiotics ===
{{See also|Medications used to treat MRSA}}
Treatment of MRSA infection is urgent, and delays can be fatal.&lt;ref name=Ficalora&gt;{{cite book | vauthors = Ficalora R | title = Mayo Clinic internal medicine board review | publisher = Oxford University Press | location = Oxford | year = 2013 | isbn = 978-0-19-994894-9 }}&lt;/ref&gt;{{rp|328}} The location and history related to the infection determines the treatment. The route of administration of an antibiotic varies. Antibiotics effective against MRSA can be given by IV, oral, or a combination of both, and depend on the specific circumstances and patient characteristics.&lt;ref name=IDSA2011 /&gt; The use of concurrent treatment with [[vancomycin]] or other [[beta-lactam]] agents may have a synergistic effect.&lt;ref name=Winn /&gt;{{rp|637}}

Both CA-MRSA and HA-MRSA are resistant to traditional anti-staphylococcal [[beta-lactam antibiotic]]s, such as [[cephalexin]]. CA-MRSA has a greater spectrum of antimicrobial susceptibility to [[sulfonamide (medicine)|sulfa drugs]] (like co-trimoxazole ([[trimethoprim/sulfamethoxazole]]), [[tetracycline antibiotics|tetracyclines]] (like [[doxycycline]] and [[minocycline]]) and [[clindamycin]] (for [[osteomyelitis]]).&lt;ref name=&quot;IDSA2011&quot; /&gt; MRSA can be eradicated with a regimen of [[linezolid]],&lt;ref name=&quot;CochraneSurg2013&quot; /&gt; though treatment protocols vary and serum levels of antibiotics vary widely from person to person and may affect outcomes.&lt;ref name=&quot;ChooChambers2016&quot;&gt;{{cite journal | vauthors = Choo EJ, Chambers HF | title = Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia | journal = Infection &amp; Chemotherapy | volume = 48 | issue = 4 | pages = 267–273 | date = December 2016 | pmid = 28032484 | pmc = 5204005 | doi = 10.3947/ic.2016.48.4.267 }}&lt;/ref&gt;
The effective treatment of MRSA with [[linezolid]] has been successful&lt;ref name=CochraneNonSurg2013 /&gt; in 87% of people. Linezolid is more effective in soft tissue infections than vancomycin.&lt;ref name=&quot;YueDong2016&quot; /&gt;&lt;ref name=&quot;CochraneSurg2013&quot; /&gt; This is compared to the eradication of infection in those with MRSA treated with vancomycin. Treatment with vancomycin is successful in approximately 49% of people.&lt;ref name=&quot;CochraneSurg2013&quot; /&gt; Linezolid belongs to the newer [[oxazolidinone]] class of antibiotics, which is effective against both CA-MRSA and HA-MRSA. The [[Infectious Disease Society of America]] recommends vancomycin, linezolid, or clindamycin (if susceptible) for treating those with MRSA pneumonia.&lt;ref name=&quot;IDSA2011&quot;&gt;{{cite journal | vauthors = Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ, Kaplan SL, Karchmer AW, Levine DP, Murray BE, J Rybak M, Talan DA, Chambers HF | title = Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children | journal = Clinical Infectious Diseases | volume = 52 | issue = 3 | pages = e18-55 | date = February 2011 | pmid = 21208910 | doi = 10.1093/cid/ciq146 | doi-access = free }}&lt;/ref&gt;
[[Ceftaroline]], a fifth-generation cephalosporin, is the first beta-lactam antibiotic approved in the US to treat MRSA infections in skin and soft tissue or community-acquired pneumonia.&lt;ref&gt;{{cite web |url=https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm231594.htm |archive-url=https://web.archive.org/web/20101101210442/http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm231594.htm |archive-date=November 1, 2010 |title=FDA Approves Teflaro for Bacterial Infections |website=[[Food and Drug Administration]] }}&lt;/ref&gt;

Vancomycin and [[teicoplanin]] are [[glycopeptide antibiotic]]s used to treat MRSA infections.&lt;ref&gt;{{cite journal | vauthors = Schentag JJ, Hyatt JM, Carr JR, Paladino JA, Birmingham MC, Zimmer GS, Cumbo TJ | title = Genesis of methicillin-resistant Staphylococcus aureus (MRSA), how treatment of MRSA infections has selected for vancomycin-resistant Enterococcus faecium, and the importance of antibiotic management and infection control | journal = Clinical Infectious Diseases | volume = 26 | issue = 5 | pages = 1204–14 | date = May 1998 | pmid = 9597254 | doi = 10.1086/520287 | doi-access = free }}&lt;/ref&gt; Teicoplanin is a structural [[congener (chemistry)|congener]] of vancomycin that has a similar activity spectrum but a longer [[biological half-life|half-life]].&lt;ref&gt;{{cite journal | vauthors = Rybak MJ, Lerner SA, Levine DP, Albrecht LM, McNeil PL, Thompson GA, Kenny MT, Yuh L | title = Teicoplanin pharmacokinetics in intravenous drug abusers being treated for bacterial endocarditis | journal = Antimicrobial Agents and Chemotherapy | volume = 35 | issue = 4 | pages = 696–700 | date = April 1991 | pmid = 1829880 | pmc = 245081 | doi = 10.1128/AAC.35.4.696 }}&lt;/ref&gt; Because the oral absorption of vancomycin and teicoplanin is very low, these agents can be administered intravenously to control systemic infections.&lt;ref&gt;{{cite journal | vauthors = Janknegt R | s2cid = 10413339 | title = The treatment of staphylococcal infections with special reference to pharmacokinetic, pharmacodynamic and pharmacoeconomic considerations | journal = Pharmacy World &amp; Science | volume = 19 | issue = 3 | pages = 133–41 | date = June 1997 | pmid = 9259029 | doi = 10.1023/A:1008609718457 }}&lt;/ref&gt; Treatment of MRSA infection with vancomycin can be complicated, due to its inconvenient route of administration. Moreover, the efficacy of vancomycin against MRSA is inferior to that of anti-staphylococcal [[beta-lactam antibiotic]]s against methicillin-susceptible ''S. aureus'' (MSSA).&lt;ref&gt;{{cite journal | vauthors = Chang FY, Peacock JE, Musher DM, Triplett P, MacDonald BB, Mylotte JM, O'Donnell A, Wagener MM, Yu VL | s2cid = 15917805 | title = Staphylococcus aureus bacteremia: recurrence and the impact of antibiotic treatment in a prospective multicenter study | journal = Medicine | volume = 82 | issue = 5 | pages = 333–9 | date = September 2003 | pmid = 14530782 | doi = 10.1097/01.md.0000091184.93122.09 | doi-access = free }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Siegman-Igra Y, Reich P, Orni-Wasserlauf R, Schwartz D, Giladi M | s2cid = 24390948 | title = The role of vancomycin in the persistence or recurrence of Staphylococcus aureus bacteraemia | journal = Scandinavian Journal of Infectious Diseases | volume = 37 | issue = 8 | pages = 572–578 | year = 2005 | pmid = 16138425 | doi = 10.1080/00365540510038488 }}&lt;/ref&gt;

Several newly discovered strains of MRSA show antibiotic resistance even to vancomycin and teicoplanin. Strains with intermediate (4–8&amp;nbsp;μg/ml) levels of resistance, termed glycopeptide-intermediate ''S. aureus'' (GISA) or [[Vancomycin-resistant Staphylococcus aureus#Vancomycin-intermediate S. aureus (VISA)|vancomycin-intermediate ''S. aureus'' (VISA)]],&lt;ref&gt;{{cite journal |vauthors=Sieradzki K, Tomasz A |date=April 1997 |title=Inhibition of cell wall turnover and autolysis by vancomycin in a highly vancomycin-resistant mutant of Staphylococcus aureus |journal=Journal of Bacteriology |volume=179 |issue=8 |pages=2557–66 |doi=10.1128/jb.179.8.2557-2566.1997 |pmc=179004 |pmid=9098053}}&lt;/ref&gt;&lt;ref&gt;{{cite journal |vauthors=Schito GC |date=March 2006 |title=The importance of the development of antibiotic resistance in Staphylococcus aureus |journal=Clinical Microbiology and Infection |volume=12 |issue=Suppl 1 |pages=3–8 |doi=10.1111/j.1469-0691.2006.01343.x |pmid=16445718 |doi-access=free}}&lt;/ref&gt; began appearing in the late 1990s. The first identified case was in Japan in 1996, and strains have since been found in hospitals in England, France, and the US. The first documented strain with complete (&gt;16&amp;nbsp;μg/ml) resistance to vancomycin, termed [[Vancomycin-resistant Staphylococcus aureus|vancomycin-resistant ''S. aureus'' (VRSA)]], appeared in the United States in 2002.&lt;ref&gt;{{cite journal |vauthors=Bozdogan B, Esel D, Whitener C, Browne FA, Appelbaum PC |date=November 2003 |title=Antibacterial susceptibility of a vancomycin-resistant Staphylococcus aureus strain isolated at the Hershey Medical Center |journal=The Journal of Antimicrobial Chemotherapy |volume=52 |issue=5 |pages=864–8 |doi=10.1093/jac/dkg457 |pmid=14563898 |doi-access=free}}&lt;/ref&gt; In 2011, a variant of vancomycin was tested that binds to the lactate variation and also binds well to the original target, thus reinstating potent antimicrobial activity.&lt;ref&gt;{{cite journal |vauthors=Xie J, Pierce JG, James RC, Okano A, Boger DL |date=September 2011 |title=A redesigned vancomycin engineered for dual D-Ala-D-ala And D-Ala-D-Lac binding exhibits potent antimicrobial activity against vancomycin-resistant bacteria |journal=Journal of the American Chemical Society |volume=133 |issue=35 |pages=13946–9 |doi=10.1021/ja207142h |pmc=3164945 |pmid=21823662}}&lt;/ref&gt; [[Linezolid]], [[quinupristin/dalfopristin]], [[daptomycin]], [[ceftaroline]], and [[tigecycline]] are used to treat more severe infections that do not respond to glycopeptides such as vancomycin.&lt;ref&gt;{{cite journal | vauthors = Mongkolrattanothai K, Boyle S, Kahana MD, Daum RS | title = Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and methicillin-resistant isolates | journal = Clinical Infectious Diseases | volume = 37 | issue = 8 | pages = 1050–8 | date = October 2003 | pmid = 14523769 | doi = 10.1086/378277 | doi-access = free }}&lt;/ref&gt; Current guidelines recommend daptomycin for VISA bloodstream infections and endocarditis.&lt;ref name=&quot;IDSA2011&quot; /&gt;

[[Linezolid|Oxazolidinones]] such as [[linezolid]] became available in the 1990s and are comparable to vancomycin in effectiveness against MRSA. Linezolid resistance in ''S. aureus'' was reported in 2001,&lt;ref&gt;{{cite journal | vauthors = Tsiodras S, Gold HS, Sakoulas G, Eliopoulos GM, Wennersten C, Venkataraman L, Moellering RC, Ferraro MJ | s2cid = 27426801 | title = Linezolid resistance in a clinical isolate of Staphylococcus aureus | journal = Lancet | volume = 358 | issue = 9277 | pages = 207–8 | date = July 2001 | pmid = 11476839 | doi = 10.1016/S0140-6736(01)05410-1 }}&lt;/ref&gt; but infection rates have been at consistently low levels. In the United Kingdom and Ireland, no linezolid resistance was found in staphylococci collected from&amp;nbsp;[[bacteremia]]&amp;nbsp;cases between 2001 and 2006.&lt;ref&gt;{{cite journal | vauthors = Hope R, Livermore DM, Brick G, Lillie M, Reynolds R | title = Non-susceptibility trends among staphylococci from bacteraemias in the UK and Ireland, 2001-06 | journal = The Journal of Antimicrobial Chemotherapy | volume = 62 | pages = ii65-74 | date = November 2008 | issue = Suppl 2 | pmid = 18819981 | doi = 10.1093/jac/dkn353 | url = http://jac.oxfordjournals.org/content/62/suppl_2/ii65.full.pdf }}&lt;/ref&gt;

=== Skin and soft-tissue infections ===
In skin abscesses, the primary treatment recommended is removal of dead tissue, incision, and drainage. More information is needed to determine the effectiveness of specific antibiotics therapy in surgical site infections (SSIs).&lt;ref name=IDSA2011 /&gt; Examples of soft-tissue infections from MRSA include ulcers, [[impetigo]], abscesses, and SSIs.&lt;ref name=&quot;YueDong2016&quot;&gt;{{cite journal | vauthors = Yue J, Dong BR, Yang M, Chen X, Wu T, Liu GJ | title = Linezolid versus vancomycin for skin and soft tissue infections | journal = The Cochrane Database of Systematic Reviews | issue = 1 | article-number = CD008056 | date = January 2016 | volume = 2016 | pmid = 26758498 | doi = 10.1002/14651858.CD008056.pub3 | pmc = 10435313 }}&lt;/ref&gt;
In surgical wounds, evidence is weak (high risk of [[bias]]) that [[linezolid]] may be better than [[vancomycin]] to eradicate MRSA SSIs.&lt;ref name=&quot;CochraneSurg2013&quot;/&gt;

MRSA colonization is also found in nonsurgical wounds such as traumatic wounds, [[burn]]s, and chronic [[ulcer]]s (i.e.: [[diabetic ulcer]], [[pressure ulcer]], [[arterial insufficiency ulcer]], [[venous ulcer]]). No conclusive evidence has been found about the best antibiotic regimen to treat MRSA colonization.&lt;ref name=&quot;CochraneNonSurg2013&quot; /&gt;

=== Children ===
In skin infections and secondary infection sites, topical [[mupirocin]] is used successfully. For bacteremia and endocarditis, vancomycin or daptomycin is considered. For children with MRSA-infected bone or joints, treatment is individualized and long-term. Neonates can develop neonatal pustulosis as a result of topical infection with MRSA.&lt;ref name=IDSA2011 /&gt; Clindamycin is not approved for the treatment of MRSA infection, but it is still used in children for soft-tissue infections.&lt;ref name=IDSA2011 /&gt;

=== Endocarditis and bacteremia ===
Evaluation for the replacement of a prosthetic valve is considered. Appropriate antibiotic therapy may be administered for up to six weeks. Four to six weeks of antibiotic treatment is often recommended, and is dependent upon the extent of MRSA infection.&lt;ref name=IDSA2011 /&gt;

=== Respiratory infections ===
CA-MRSA in hospitalized patients pneumonia treatment begins before culture results. After the susceptibility to antibiotics is performed, the infection may be treated with vancomycin or linezolid for up to 21 days. If the pneumonia is complicated by the accumulation of pus in the pleural cavity surrounding the lungs, drainage may be done along with antibiotic therapy.&lt;ref name=IDSA2011 /&gt; People with cystic fibrosis may develop respiratory complications related to MRSA infection. The incidence of MRSA in those with cystic fibrosis increased from 2000 to 2015 by five times. Most of these infections were HA-MRSA. MRSA accounts for 26% of lung infections in those with cystic fibrosis.&lt;ref name=&quot;MaselliKeyt2017&quot;&gt;{{cite journal | vauthors = Maselli DJ, Keyt H, Restrepo MI | title = Inhaled Antibiotic Therapy in Chronic Respiratory Diseases | journal = International Journal of Molecular Sciences | volume = 18 | issue = 5 | page = 1062 | date = May 2017 | pmid = 28509852 | pmc = 5454974 | doi = 10.3390/ijms18051062 | doi-access = free }}&lt;/ref&gt;

There is insufficient evidence to support the use of topical or systemic antibiotics for nasal or extra-nasal MRSA infection.&lt;ref&gt;{{cite journal | vauthors = Loeb MB, Main C, Eady A, Walker-Dilks C | title = Antimicrobial drugs for treating methicillin-resistant Staphylococcus aureus colonization | journal = The Cochrane Database of Systematic Reviews | issue = 4 | article-number = CD003340 | date = 2003-10-20 | pmid = 14583969 | doi = 10.1002/14651858.CD003340 | collaboration = Cochrane Wounds Group }}&lt;/ref&gt;

=== Bone and joint infections ===
Cleaning the wound of dead tissue and draining abscesses is the first action to treat the MRSA infection. Administration of antibiotics is not standardized and is adapted on a case-by-case basis. Antibiotic therapy can last up to 3 months and sometimes even longer.&lt;ref name=IDSA2011 /&gt;

=== Infected implants ===
MRSA infection can occur in association with implants and joint replacements. Recommendations on treatment are based upon the length of time the implant has been in place. In cases of a recent placement of a surgical implant or artificial joint, the device may be retained while antibiotic therapy continues. If the placement of the device occurred over 3 weeks ago, the device may be removed. Antibiotic therapy is used in each instance, sometimes long-term.&lt;ref name=IDSA2011 /&gt;

=== Central nervous system ===
MRSA can infect the central nervous system and form brain abscess, subdural empyema, and spinal epidural abscess. Excision and drainage can be done along with antibiotic treatment. Septic thrombosis of cavernous or [[dural venous sinus]] can sometimes be a complication.&lt;ref name=IDSA2011 /&gt;

=== Other infections ===
Treatment is not standardized for other instances of MRSA infection in a wide range of tissues. Treatment varies for MRSA infections related to: subperiosteal abscesses, necrotizing pneumonia, cellulitis, pyomyositis, necrotizing fasciitis, mediastinitis, myocardial, perinephric, hepatic, and splenic abscesses, septic thrombophlebitis, and severe ocular infections, including endophthalmitis.&lt;ref name=IDSA2011 /&gt; Pets can be reservoirs and pass on MRSA to people. In some cases, the infection can be symptomatic, and the pet can develop an MRSA infection. Health departments recommend that the pet be taken to the veterinarian if MRSA infections keep occurring in the people who have contact with the pet.&lt;ref name=tpchd /&gt;

== Epidemiology ==
Worldwide, an estimated 2&amp;nbsp;billion people carry some form of ''S. aureus''; of these, up to 53&amp;nbsp;million (2.7% of carriers) are thought to carry MRSA.&lt;ref&gt;{{cite web |url= http://www.keepkidshealthy.com/welcome/infectionsguide/mrsa.html |title= MRSA Infections |publisher= Keep Kids Healthy| archive-url= https://web.archive.org/web/20071209022625/https://keepkidshealthy.com/welcome/infectionsguide/mrsa.html | archive-date=December 9, 2007 }}&lt;/ref&gt; ''S. aureus'' was identified as one of the six leading pathogens for deaths associated with resistance in 2019 and 100,000 deaths caused by MRSA were attributable to antimicrobial resistance.&lt;ref&gt;{{cite journal | title = Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis | language = English | journal = Lancet | volume = 399 | issue = 10325 | pages = 629–655 | date = February 2022 | pmid = 35065702 | pmc = 8841637 | doi = 10.1016/S0140-6736(21)02724-0 | vauthors = Murray CJ, Ikuta KS, Sharara F, Swetschinski L, Robles Aguilar G, Gray A, Han C, Bisignano C, Rao P, Wool E, Johnson SC, Browne AJ, Chipeta MG, Fell F, Hackett S, Haines-Woodhouse G, Kashef Hamadani BH, Kumaran EA, McManigal B, Achalapong S, Agarwal R, Akech S, Albertson S, Amuasi J, Andrews J, Aravkin A, Ashley E, Babin F, Bailey F, Baker S | collaboration = Antimicrobial Resistance Collaborators }}&lt;/ref&gt;

=== HA-MRSA (healthcare-associated) ===
In a US cohort study of 1,300 healthy children, 2.4% carried MRSA in their nose.&lt;ref name=&quot;auto&quot;&gt;{{cite journal | vauthors = Fritz SA, Garbutt J, Elward A, Shannon W, Storch GA | s2cid = 23112235 | title = Prevalence of and risk factors for community-acquired methicillin-resistant and methicillin-sensitive staphylococcus aureus colonization in children seen in a practice-based research network | journal = Pediatrics | volume = 121 | issue = 6 | pages = 1090–8 | date = June 2008 | pmid = 18519477 | doi = 10.1542/peds.2007-2104 }}&lt;/ref&gt; Bacterial sepsis occurs with most (75%) of cases of invasive MRSA infection.&lt;ref name=IDSA2011 /&gt; In 2009, there were an estimated 463,017 hospitalizations due to MRSA, or a rate of 11.74 per 1,000 hospitalizations.&lt;ref name=klein2013&gt;{{cite journal | vauthors = Klein EY, Sun L, Smith DL, Laxminarayan R | title = The changing epidemiology of methicillin-resistant Staphylococcus aureus in the United States: a national observational study | journal = American Journal of Epidemiology | volume = 177 | issue = 7 | pages = 666–74 | date = April 2013 | pmid = 23449778 | doi = 10.1093/aje/kws273 | doi-access = free }}&lt;/ref&gt; Many of these infections are less serious, but the Centers for Disease Control and Prevention (CDC) estimate that there are 80,461 invasive MRSA infections and 11,285 deaths due to MRSA annually.&lt;ref&gt;{{cite web|url=https://www.cdc.gov/drugresistance/threat-report-2013/|title=Antibiotic Resistance Threats in the United States, 2013 – Antibiotic/Antimicrobial Resistance – CDC|date=2019-05-07}}{{CDC}}&lt;/ref&gt; In 2003, the cost for a hospitalization due to MRSA infection was US$92,363; a hospital stay for MSSA was $52,791.&lt;ref name=&quot;YueDong2016&quot; /&gt;

Infection after surgery is relatively uncommon, but occurs as much as 33% in specific types of surgeries. Infections of surgical sites range from 1% to 33%. MRSA sepsis that occurs within 30 days following a surgical infection has a 15–38% mortality rate; MRSA sepsis that occurs within one year has a mortality rate of around 55%. There may be increased mortality associated with cardiac surgery. There is a rate of 12.9% in those infected with MRSA, while only 3% infected with other organisms. SSIs infected with MRSA had longer hospital stays than those who did not.&lt;ref name= CochraneSurg2013 /&gt;

Globally, MRSA infection rates are dynamic and vary year to year.&lt;ref&gt;{{cite web|url=https://resistancemap.cddep.org/AntibioticResistance.php|title=ResistanceMap – Antibiotic Resistance|publisher = Center for Disease Dynamics, Economics &amp; Policy | date = 2017|website=resistancemap.cddep.org|access-date=27 May 2017}} note: a search must be performed on the website; it is interactive and the statistics are based upon the most current information,&lt;/ref&gt; According to the 2006 SENTRY Antimicrobial Surveillance Program report, the incidence of MRSA bloodstream infections was 35.9% in North America. MRSA blood infections in Latin America were 29%. European incidence was 22.8%. The rate of all MRSA infections in Europe ranged from 50% in Portugal down to 0.8% in Sweden. Overall MRSA infection rates varied in Latin America: Colombia and Venezuela combined had 3%, Mexico had 50%, Chile 38%, Brazil 29%, and Argentina 28%.&lt;ref name=&quot;YueDong2016&quot; /&gt;

The [[Centers for Disease Control and Prevention]] (CDC) estimated that about 1.7&amp;nbsp;million nosocomial infections occurred in the United States in 2002, with 99,000 associated deaths.&lt;ref&gt;{{cite journal | vauthors = Klevens RM, Edwards JR, Richards CL, Horan TC, Gaynes RP, Pollock DA, Cardo DM | title = Estimating health care-associated infections and deaths in U.S. hospitals, 2002 | journal = Public Health Reports | volume = 122 | issue = 2 | pages = 160–6 | year = 2007 | pmid = 17357358 | pmc = 1820440 | doi = 10.1177/003335490712200205 }}&lt;/ref&gt; The estimated incidence is 4.5 nosocomial infections per 100 admissions, with direct costs (at 2004 prices) ranging from $10,500 (£5300, €8000 at 2006 rates) per case (for bloodstream, urinary tract, or respiratory infections in immunocompetent people) to $111,000 (£57,000, €85,000) per case for antibiotic-resistant infections in the bloodstream in people with transplants. With these numbers, conservative estimates of the total direct costs of nosocomial infections are above $17&amp;nbsp;billion. The reduction of such infections forms an important component of efforts to improve healthcare safety. (BMJ 2007){{Citation needed|reason=proper citing|date=February 2009}} MRSA alone was associated with 8% of nosocomial infections reported to the CDC National Healthcare Safety Network from January 2006 to October 2007.&lt;ref name=&quot;pmid18947320&quot;&gt;{{cite journal | vauthors = Hidron AI, Edwards JR, Patel J, Horan TC, Sievert DM, Pollock DA, Fridkin SK | title = NHSN annual update: antimicrobial-resistant pathogens associated with healthcare-associated infections: annual summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2006–2007 | journal = Infection Control and Hospital Epidemiology | volume = 29 | issue = 11 | pages = 996–1011 | date = November 2008 | pmid = 18947320 | doi = 10.1086/591861 | s2cid = 205988392 }}&lt;/ref&gt;

The [[British National Audit Office]] estimated that the incidence of nosocomial infections in Europe ranges from 4% to 10% of all hospital admissions. As of early 2005, the number of deaths in the United Kingdom attributed to MRSA has been estimated by various sources to lie in the range of 3,000 per year.&lt;ref&gt;{{cite journal | vauthors = Johnson AP, Pearson A, Duckworth G | title = Surveillance and epidemiology of MRSA bacteraemia in the UK | journal = The Journal of Antimicrobial Chemotherapy | volume = 56 | issue = 3 | pages = 455–62 | date = September 2005 | pmid = 16046464 | doi = 10.1093/jac/dki266 | doi-access = free }}&lt;/ref&gt;

In the United States, an estimated 95&amp;nbsp;million people carry ''S. aureus'' in their noses; of these, 2.5&amp;nbsp;million (2.6% of carriers) carry MRSA.&lt;ref&gt;{{cite journal | vauthors = Graham PL, Lin SX, Larson EL | s2cid = 38816447 | title = A U.S. population-based survey of Staphylococcus aureus colonization | journal = Annals of Internal Medicine | volume = 144 | issue = 5 | pages = 318–25 | date = March 2006 | pmid = 16520472 | doi = 10.7326/0003-4819-144-5-200603070-00006 }}&lt;/ref&gt; A population review conducted in three U.S. communities showed the annual incidence of CA-MRSA during 2001–2002 to be 18–25.7/100,000; most CA-MRSA isolates were associated with clinically relevant infections, and 23% of people required hospitalization.&lt;ref&gt;{{cite conference |vauthors=Jernigan JA, Arnold K, Heilpern K, Kainer M, Woods C, Hughes JM |title= Methicillin-resistant ''Staphylococcus aureus'' as community pathogen |book-title= Symposium on Community-Associated Methicillin-resistant ''Staphylococcus aureus'' (Atlanta, Georgia, U.S.). Cited in Emerg Infect Dis |publisher= Centers for Disease Control and Prevention |date=2006-05-12 |url= https://www.cdc.gov/ncidod/EID/vol12no11/06-0911.htm |access-date= 2007-01-27}}&lt;/ref&gt;

=== CA-MRSA (community-associated) ===
In a US cohort study of 1,300 healthy children, 2.4% carried MRSA in their noses.&lt;ref name=&quot;auto&quot; /&gt; There are concerns that the presence of MRSA in the environment may allow resistance to be transferred to other bacteria through [[bacteriophage|phages]] (viruses that infect bacteria). The source of MRSA could come from hospital waste, farm sewage, or other wastewater.&lt;ref name=IDSA2011 /&gt; MRSA is also common in infections of dogs and cats, and transmission to humans can occur, since pet owners hug and kiss their pets or let them sleep in their beds.&lt;ref name = Feuer2024&gt;{{Cite journal| doi = 10.1093/jac/dkae225| issn = 1460-2091| pages = –225| last1 = Feuer| first1 = Leonie| last2 = Frenzer| first2 = Stefanie Katharina| last3 = Merle| first3 = Roswitha| last4 = Leistner| first4 = Rasmus| last5 = Bäumer| first5 = Wolfgang| last6 = Bethe| first6 = Astrid| last7 = Lübke-Becker| first7 = Antina| last8 = Klein| first8 = Babette| last9 = Bartel| first9 = Alexander| title = Prevalence of MRSA in canine and feline clinical samples from one-third of veterinary practices in Germany from 2019-2021| journal = The Journal of Antimicrobial Chemotherapy| date = 2024-07-15| volume = 79| issue = 9| pmid = 39007221}}&lt;/ref&gt; While sharing of isolates can occur, infections in humans seem to originate from HA-MRSA rather than from pet-acquired CA-MRSA.&lt;ref&gt;{{Cite journal |last1=Genath |first1=Antonia |last2=Hackmann |first2=Carolin |last3=Denkel |first3=Luisa |last4=Weber |first4=Anna |last5=Maechler |first5=Friederike |last6=Kola |first6=Axel |last7=Schwarz |first7=Stefan |last8=Gastmeier |first8=Petra |last9=Leistner |first9=Rasmus |date=2024-09-20 |title=The genetic relationship between human and pet isolates: a core genome multilocus sequence analysis of multidrug-resistant bacteria |journal=Antimicrobial Resistance &amp; Infection Control |language=en |volume=13 |issue=1 |page=107 |doi=10.1186/s13756-024-01457-7 |doi-access=free |issn=2047-2994 |pmc=11416027 |pmid=39304920}}&lt;/ref&gt;

=== LA-MRSA (livestock-associated) ===
In 2004, MRSA was first isolated on a Dutch pig farm leading to further investigations of livestock associated MRSA (LA-MRSA).&lt;ref&gt;{{cite journal | vauthors = Voss A, Loeffen F, Bakker J, Klaassen C, Wulf M | title = Methicillin-resistant Staphylococcus aureus in pig farming | language = en-us | journal = Emerging Infectious Diseases | volume = 11 | issue = 12 | pages = 1965–1966 | date = December 2005 | pmid = 16485492 | pmc = 3367632 | doi = 10.3201/eid1112.050428 }}&lt;/ref&gt; Livestock associated MRSA (LA-MRSA) has been observed in Korea, Brazil, Switzerland, Malaysia, India, Great Britain, Denmark, and China.&lt;ref name = Gopal2017 /&gt;

== History ==
[[File:EARS-Net CAESAR MRSA 2017-en.svg|thumb|Incidence of MRSA in human blood samples in countries which took part in the study in 2017]]
In 1961, the first known MRSA isolates were reported in a British study, and from 1961 to 1967, infrequent hospital outbreaks occurred in Western Europe and Australia,&lt;ref name=&quot;The University of Chicago Medical Center&quot;&gt;{{cite web |url=http://mrsa-research-center.bsd.uchicago.edu/timeline.html |publisher=The University of Chicago Medical Center |title=MRSA History Timeline: The First Half-Century, 1959–2009 |year=2010 |access-date=2012-04-24 |archive-date=2020-02-18 |archive-url=https://web.archive.org/web/20200218151301/http://mrsa-research-center.bsd.uchicago.edu/timeline.html }}&lt;/ref&gt; with [[methicillin]] then being licensed in England to treat resistant infections. Other reports of MRSA began to be described in the 1970s.&lt;ref name = CochraneSurg2013 /&gt; Resistance to other antibiotics was documented in some strains of ''S. aureus''. In 1996, [[vancomycin]] resistance was reported in Japan.&lt;ref name=Winn /&gt;{{rp|637}} In many countries, outbreaks of MRSA infection were reported to be transmitted between hospitals.&lt;ref name=Murray /&gt;{{rp|402}} The rate had increased to 22% by 1995, and by 1997 the level of hospital ''S. aureus'' infections attributable to MRSA had reached 50%.

The first reports of community-associated MRSA (CA-MRSA) occurred in 1981 and 1982, a large outbreak of CA-MRSA occurred among intravenous drug users in Detroit, Michigan.&lt;ref name=&quot;The University of Chicago Medical Center&quot; /&gt; Additional outbreaks of CA-MRSA were reported through the 1980s and 1990s, including outbreaks among Australian Aboriginal populations that had never been exposed to hospitals. In the mid-1990s, scattered reports of CA-MRSA outbreaks among US children were made. While HA-MRSA rates stabilized between 1998 and 2008, CA-MRSA rates continued to rise. A report released by the University of Chicago Children's Hospital comparing two periods (1993–1995 and 1995–1997) found a 25-fold increase in the rate of hospitalizations due to MRSA among children in the United States.&lt;ref&gt;{{cite web|url=http://mrsa-research-center.bsd.uchicago.edu/JAMA_02_25_1998_issue.pdf|title=Community-acquired MRSA in Children with no predisposing risk|access-date=2012-04-24|archive-date=2017-12-09|archive-url=https://web.archive.org/web/20171209095638/http://mrsa-research-center.bsd.uchicago.edu/JAMA_02_25_1998_issue.pdf}}&lt;/ref&gt; In 1999, the University of Chicago reported the first deaths from invasive MRSA among otherwise healthy children in the United States.&lt;ref name=&quot;The University of Chicago Medical Center&quot; /&gt; By 2004, the genome for various strains of MRSA were described.&lt;ref&gt;{{cite journal | vauthors = Holden MT, Feil EJ, Lindsay JA, Peacock SJ, Day NP, Enright MC, Foster TJ, Moore CE, Hurst L, Atkin R, Barron A, Bason N, Bentley SD, Chillingworth C, Chillingworth T, Churcher C, Clark L, Corton C, Cronin A, Doggett J, Dowd L, Feltwell T, Hance Z, Harris B, Hauser H, Holroyd S, Jagels K, James KD, Lennard N, Line A, Mayes R, Moule S, Mungall K, Ormond D, Quail MA, Rabbinowitsch E, Rutherford K, Sanders M, Sharp S, Simmonds M, Stevens K, Whitehead S, Barrell BG, Spratt BG, Parkhill J | title = Complete genomes of two clinical Staphylococcus aureus strains: evidence for the rapid evolution of virulence and drug resistance | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 101 | issue = 26 | pages = 9786–91 | date = June 2004 | pmid = 15213324 | pmc = 470752 | doi = 10.1073/pnas.0402521101 | bibcode = 2004PNAS..101.9786H | doi-access = free }}&lt;/ref&gt;

The observed increased mortality among MRSA-infected people arguably may be the result of the increased underlying [[morbidity]] of these people. Several studies, however, including one by Blot and colleagues, that have adjusted for underlying disease still found MRSA bacteremia to have a higher attributable mortality than methicillin-susceptible ''S. aureus'' (MSSA) bacteremia.&lt;ref&gt;{{cite journal | vauthors = Blot SI, Vandewoude KH, Hoste EA, Colardyn FA | title = Outcome and attributable mortality in critically Ill patients with bacteremia involving methicillin-susceptible and methicillin-resistant Staphylococcus aureus | journal = Archives of Internal Medicine | volume = 162 | issue = 19 | pages = 2229–35 | date = October 2002 | pmid = 12390067 | doi = 10.1001/archinte.162.19.2229 | doi-access = free }}&lt;/ref&gt;

A population-based study of the incidence of MRSA infections in [[San Francisco]] during 2004–05 demonstrated that nearly one in 300 residents had such an infection in a year and that greater than 85% of these infections occurred outside of the healthcare setting.&lt;ref&gt;{{cite journal | vauthors = Liu C, Graber CJ, Karr M, Diep BA, Basuino L, Schwartz BS, Enright MC, O'Hanlon SJ, Thomas JC, Perdreau-Remington F, Gordon S, Gunthorpe H, Jacobs R, Jensen P, Leoung G, Rumack JS, Chambers HF | title = A population-based study of the incidence and molecular epidemiology of methicillin-resistant Staphylococcus aureus disease in San Francisco, 2004–2005 | journal = Clinical Infectious Diseases | volume = 46 | issue = 11 | pages = 1637–46 | date = June 2008 | pmid = 18433335 | doi = 10.1086/587893 | doi-access = free }}&lt;/ref&gt; A 2004 study showed that people in the United States with ''S. aureus'' infection had, on average, three times the length of hospital stay (14.3 vs. 4.5 days), incurred three times the total cost ($48,824 vs. $14,141), and experienced five times the risk of in-hospital death (11.2% vs 2.3%) than people without this infection.&lt;ref&gt;{{cite journal | vauthors = Noskin GA, Rubin RJ, Schentag JJ, Kluytmans J, Hedblom EC, Smulders M, Lapetina E, Gemmen E | title = The burden of Staphylococcus aureus infections on hospitals in the United States: an analysis of the 2000 and 2001 Nationwide Inpatient Sample Database | journal = Archives of Internal Medicine | volume = 165 | issue = 15 | pages = 1756–61 | year = 2005 | pmid = 16087824 | doi = 10.1001/archinte.165.15.1756 | doi-access = free }}&lt;/ref&gt; In a meta-analysis of 31 studies, Cosgrove ''et al.'',&lt;ref&gt;{{cite journal | vauthors = Cosgrove SE, Qi Y, Kaye KS, Harbarth S, Karchmer AW, Carmeli Y | title = The impact of methicillin resistance in Staphylococcus aureus bacteremia on patient outcomes: mortality, length of stay, and hospital charges | journal = Infection Control and Hospital Epidemiology | volume = 26 | issue = 2 | pages = 166–74 | date = February 2005 | pmid = 15756888 | doi = 10.1086/502522 | s2cid = 22553908 }}&lt;/ref&gt; concluded that MRSA bacteremia is associated with increased mortality as compared with MSSA bacteremia (odds ratio= 1.93; 95% {{nowrap|CI {{=}}
1.93 ± 0.39}}).&lt;ref&gt;{{cite journal | vauthors = Hardy KJ, Hawkey PM, Gao F, Oppenheim BA | title = Methicillin resistant Staphylococcus aureus in the critically ill | journal = British Journal of Anaesthesia | volume = 92 | issue = 1 | pages = 121–30 | date = January 2004 | pmid = 14665563 | doi = 10.1093/bja/aeh008 | doi-access = free }}&lt;/ref&gt; In addition, Wyllie ''et al.'' report a death rate of 34% within 30 days among people infected with MRSA, a rate similar to the death rate of 27% seen among MSSA-infected people.&lt;ref&gt;{{cite journal | vauthors = Wyllie DH, Crook DW, Peto TE | title = Mortality after Staphylococcus aureus bacteraemia in two hospitals in Oxfordshire, 1997–2003: cohort study | journal = BMJ | volume = 333 | issue = 7562 | page = 281 | date = August 2006 | pmid = 16798756 | pmc = 1526943 | doi = 10.1136/bmj.38834.421713.2F }}&lt;/ref&gt;

In the US, the CDC issued guidelines on October 19, 2006, citing the need for additional research, but declined to recommend such screening.&lt;ref&gt;{{cite web|url=https://www.cdc.gov/ncidod/dhqp/pdf/ar/mdroGuideline2006.pdf|title=Healthcare-associated infections—HAI—CDC|work=cdc.gov|date=2019-06-03}}&lt;/ref&gt;
According to the CDC, the most recent estimates of the incidence of healthcare-associated infections that are attributable to MRSA in the United States indicate a decline in such infection rates. Incidence of MRSA central line-associated bloodstream infections as reported by hundreds of intensive care units decreased 50–70% from 2001 to 2007.&lt;ref name=&quot;mrsa-surveillance&quot;&gt;{{cite web|url=https://www.cdc.gov/mrsa/statistics/MRSA-Surveillance-Summary.html|title=MRSA Surveillance|date=April 8, 2011|publisher=Centers for Disease Control and Prevention}}&lt;/ref&gt; A separate system tracking all hospital MRSA bloodstream infections found an overall 34% decrease between 2005 and 2008.&lt;ref name=&quot;mrsa-surveillance&quot; /&gt; In 2010, vancomycin was the drug of choice.&lt;ref name=IDSA2011 /&gt;

Across Europe, based mostly on data from 2013, seven countries (Iceland, Norway, Sweden, the Netherlands, Denmark, Finland, and Estonia, from lowest to highest) had low levels of hospital-acquired MRSA infections compared to the others,&lt;ref name=EHCI2015&gt;{{cite news|title=Outcomes in EHCI 2015|url=http://www.healthpowerhouse.com/files/EHCI_2015/EHCI_2015_report.pdf|access-date=27 January 2016|publisher=Health Consumer Powerhouse|date=26 January 2016|archive-url=https://web.archive.org/web/20170606082345/http://www.healthpowerhouse.com/files/EHCI_2015/EHCI_2015_report.pdf|archive-date=6 June 2017}}&lt;/ref&gt;{{rp|92–93}} and among countries with higher levels, significant improvements had been made only in Bulgaria, Poland, and the British Isles.&lt;ref name=EHCI2015 /&gt;{{rp|40}}

A 1,000-year-old [[collyrium|eye salve]] recipe found in the medieval ''[[Bald's Leechbook]]'' at the [[British Library]], one of the earliest known medical textbooks, was found to have activity against MRSA ''in vitro'' and in skin wounds in mice.&lt;ref&gt;{{cite journal | vauthors = Harrison F, Roberts AE, Gabrilska R, Rumbaugh KP, Lee C, Diggle SP | title = A 1,000-Year-Old Antimicrobial Remedy with Antistaphylococcal Activity | journal = mBio | volume = 6 | issue = 4 | pages = e01129 | date = August 2015 | pmid = 26265721 | pmc = 4542191 | doi = 10.1128/mBio.01129-15 }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Anonye BO, Nweke V, Furner-Pardoe J, Gabrilska R, Rafiq A, Ukachukwu F, Bruce J, Lee C, Unnikrishnan M, Rumbaugh KP, Snyder LA, Harrison F | title = The safety profile of Bald's eyesalve for the treatment of bacterial infections | journal = Scientific Reports | volume = 10 | issue = 1 | article-number = 17513 | date = October 2020 | pmid = 33060666 | pmc = 7562736 | doi = 10.1038/s41598-020-74242-2 | bibcode = 2020NatSR..1017513A }}&lt;/ref&gt;&lt;ref&gt;{{cite web | vauthors = Thompson N, Smith-Spark L |title=Thousand-year-old Anglo-Saxon potion kills MRSA superbug|url=https://edition.cnn.com/2015/03/31/health/anglo-saxon-potion-mrsa/index.html|website=CNN News|date=31 March 2015 |publisher=CNN/Time Warner|access-date=1 April 2015}}&lt;/ref&gt;

== In the media ==
MRSA is frequently a media topic, especially if well-known personalities have announced that they have or have had the infection.&lt;ref&gt;{{cite web|url=https://www.tampabay.com/sports/football/bucs/bucs-carl-nicks-lawrence-tynes-have-mrsa-infections/2137793/|title=Bucs' Nicks, Tynes have MRSA infections|website=Tampa Bay Times|access-date=3 June 2017}}&lt;/ref&gt;&lt;ref&gt;{{cite web|url=http://www.cnn.com/2015/10/12/health/mrsa-bacteria/index.html|title=MRSA: The tiny bacteria that can tackle giants| vauthors = Cohen E |website=CNN|date=12 October 2015|access-date=3 June 2017}}&lt;/ref&gt;&lt;ref&gt;{{cite news|url=https://gizmodo.com/this-australian-says-he-and-his-dead-friend-invented-bi-1746958692|title=This Australian Says He and His Dead Friend Invented Bitcoin| vauthors = Biddle S, Cush A |newspaper=Gizmodo|access-date=3 June 2017}}&lt;/ref&gt; Word of outbreaks of infection appears regularly in newspapers and television news programs. A report on skin and soft-tissue infections in the [[Cook County, Illinois|Cook County]] jail in [[Chicago]] in 2004–05 demonstrated MRSA was the most common cause of these infections among those incarcerated there.&lt;ref name=&quot;:2&quot;&gt;{{cite journal | vauthors = Singh J, Johnson RC, Schlett CD, Elassal EM, Crawford KB, Mor D, Lanier JB, Law NN, Walters WA, Teneza-Mora N, Bennett JW, Hall ER, Millar EV, Ellis MW, Merrell DS | title = Multi-Body-Site Microbiome and Culture Profiling of Military Trainees Suffering from Skin and Soft Tissue Infections at Fort Benning, Georgia | journal = mSphere | volume = 1 | issue = 5 | pages = e00232–16 | date = 2016-10-26 | pmid = 27747300 | pmc = 5064451 | doi = 10.1128/mSphere.00232-16 }}&lt;/ref&gt; Lawsuits filed against those who are accused of infecting others with MRSA are also popular stories in the media.&lt;ref&gt;{{cite web|url=http://www.aboutlawsuits.com/hospital-infection-lawsuits-are-on-the-rise-1914/|title=Hospital Infection Lawsuits are on the Rise – AboutLawsuits.com|website=www.aboutlawsuits.com|date=2 December 2008|access-date=3 June 2017}}&lt;/ref&gt;&lt;ref&gt;{{cite web|url=http://www.nydailynews.com/news/mrsa-superbug-doctor-named-misdiagnosis-lawsuits-article-1.259477|title=Doc who treated superbug vic was sued before|website=[[New York Daily News]]|date=November 2007 |access-date=3 June 2017|last=Lemire|first=Jonathan}}&lt;/ref&gt;

MRSA is the topic of radio programs,&lt;ref&gt;{{Cite web|title=Staph Retreat|url=https://www.radiolab.org/podcast/staph-retreat|website=Radiolab Podcasts {{!}} WNYC Studios|access-date=2025-11-30|language=en}}&lt;/ref&gt;&lt;ref&gt;{{cite news|url=https://www.npr.org/2010/03/23/124999740/mrsa-the-drug-resistant-superbug-that-wont-die|title=MRSA: The Drug-Resistant 'Superbug' That Won't Die|website=NPR.org|access-date=3 June 2017}}&lt;/ref&gt; television shows,&lt;ref&gt;{{cite web|url=https://www.imdb.com/title/tt0771556/?ref_=fn_al_tt_1|title=&quot;Should I Worry About...?&quot; MRSA (TV Episode 2004)|website=[[IMDb]]|date=23 September 2004|access-date=3 June 2017}}&lt;/ref&gt;&lt;ref&gt;{{cite magazine|url=https://www.wired.com/2015/02/resistance-release/|title=Resistance: The Movie That Will Make You Care About Antibiotic Misuse| vauthors = McKenna M |magazine=Wired|access-date=3 June 2017}}&lt;/ref&gt;&lt;ref&gt;{{cite web|url=http://www.digitalspy.com/tv/line-of-duty/feature/a805973/line-of-duty-series-4-release-date-cast-and-everything-you-need-to-know-as-it-moves-to-bbc-one/|title=Line of Duty series 4: Everything you need to know|website=[[Digital Spy]]|date=24 April 2017|access-date=3 June 2017}}&lt;/ref&gt; books,&lt;ref&gt;{{cite book|title=Superbug: The Fatal Menace of MRSA |date=1 February 2011|publisher=Free Press|isbn=978-1-4165-5728-9|url-access=registration|url=https://archive.org/details/superbugfatalmen0000mcke}}&lt;/ref&gt; and movies.&lt;ref&gt;{{cite web|url=http://www.huffingtonpost.co.uk/juliet-gellatley/facing-the-future-of-anti_b_10927382.html|title=Facing the Future of Antibiotic Resistance – The Change Starts Here|website=HuffPost UK|date=18 July 2016|access-date=3 June 2017}}&lt;/ref&gt;

== Research ==
Various antibacterial chemical extracts from various species of the sweetgum tree (genus ''[[Liquidambar]]'') have been investigated for their activity in inhibiting MRSA. Specifically, these are: [[cinnamic acid]], cinnamyl cinnamate, [[ethyl cinnamate]], [[benzyl cinnamate]], [[styrene]], [[vanillin]], [[cinnamyl alcohol]], 2-phenylpropyl alcohol, and 3-phenylpropyl cinnamate.&lt;ref name=&quot;CrandallLingbeck2015&quot;&gt;{{cite journal | vauthors = Lingbeck JM, O'Bryan CA, Martin EM, Adams JP, Crandall PG | title = Sweetgum: An ancient source of beneficial compounds with modern benefits | journal = Pharmacognosy Reviews | volume = 9 | issue = 17 | pages = 1–11 | year = 2015 | pmid = 26009686 | pmc = 4441155 | doi = 10.4103/0973-7847.156307 | doi-access = free }}&lt;/ref&gt;

The delivery of inhaled antibiotics along with systematic administration to treat MRSA is being developed. This may improve the outcomes of those with [[cystic fibrosis]] and other respiratory infections.&lt;ref name=&quot;MaselliKeyt2017&quot; /&gt; [[Phage therapy]] has been used for years in MRSA in eastern countries, and studies are ongoing in western countries.&lt;ref&gt;{{cite journal | vauthors = Reardon S | title = Phage therapy gets revitalized | journal = Nature | volume = 510 | issue = 7503 | pages = 15–16 | date = June 2014 | pmid = 24899282 | doi = 10.1038/510015a | s2cid = 205081324 | doi-access = free | bibcode = 2014Natur.510...15R }}&lt;/ref&gt;&lt;ref&gt;{{cite web|url=http://www.bbc.com/future/story/20161115-the-viruses-that-may-save-humanity|title=The viruses that may save humanity| vauthors = Robson D |date=15 November 2016 |language=en|access-date=2018-09-25}}&lt;/ref&gt; [[Host-directed therapeutics]], including host kinase inhibitors, as well as [[antimicrobial peptides]] are under study as adjunctive or alternative treatment for MRSA.&lt;ref&gt;{{cite journal | vauthors = van den Biggelaar RH, Walburg KV, van den Eeden SJ, van Doorn CL, Meiler E, de Ries AS, Meijer AH, Ottenhoff TH, Saris A | title = Identification of kinase modulators as host-directed therapeutics against intracellular methicillin-resistant ''Staphylococcus aureus'' | journal = Frontiers in Cellular and Infection Microbiology | volume = 14 | article-number = 1367938 | date = 2024 | pmid = 38590439 | pmc = 10999543 | doi = 10.3389/fcimb.2024.1367938 | doi-access = free }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Bravo-Santano N, Stölting H, Cooper F, Bileckaja N, Majstorovic A, Ihle N, Mateos LM, Calle Y, Behrends V, Letek M | title = Host-directed kinase inhibitors act as novel therapies against intracellular Staphylococcus aureus | journal = Scientific Reports | volume = 9 | issue = 1 | article-number = 4876 | date = March 2019 | pmid = 30890742 | pmc = 6425000 | doi = 10.1038/s41598-019-41260-8 | bibcode = 2019NatSR...9.4876B }}&lt;/ref&gt;&lt;ref&gt;{{cite journal | vauthors = Scheper H, Wubbolts JM, Verhagen JA, de Visser AW, van der Wal RJ, Visser LG, de Boer MG, Nibbering PH | title = SAAP-148 Eradicates MRSA Persisters Within Mature Biofilm Models Simulating Prosthetic Joint Infection | journal = Frontiers in Microbiology | volume = 12 | article-number = 625952 | date = 2021-01-29 | pmid = 33584628 | doi = 10.3389/fmicb.2021.625952 | doi-access = free | pmc = 7879538 | hdl = 1887/3196064 | hdl-access = free }}&lt;/ref&gt;

A 2015 [[Cochrane (organisation)|Cochrane]] [[systematic review]] aimed to assess the effectiveness of wearing gloves, gowns, and masks to help stop the spread of MRSA in hospitals; however, no eligible studies were identified for inclusion. The review authors concluded that there is a need for [[randomized controlled trial]]s to be conducted to help determine if the use of gloves, gowns, and masks reduces the transmission of MRSA in hospitals.&lt;ref&gt;{{cite journal | vauthors = López-Alcalde J, Mateos-Mazón M, Guevara M, Conterno LO, Solà I, Cabir Nunes S, Bonfill Cosp X | title = Gloves, gowns and masks for reducing the transmission of meticillin-resistant Staphylococcus aureus (MRSA) in the hospital setting | journal = The Cochrane Database of Systematic Reviews | issue = 7 | article-number = CD007087 | date = July 2015 | volume = 2015 | pmid = 26184396 | pmc = 7026606 | doi = 10.1002/14651858.cd007087.pub2 }}&lt;/ref&gt;

==See also==
* [[MRSA ST398]]

== References ==
{{Reflist}}

== Further reading ==
{{Commons category|Methicillin-resistant Staphylococcus aureus|MRSA}}
* [https://www.cdc.gov/mrsa/ The Centers for Disease Control and Prevention] information, prevention, statistics, at risk groups, causes, educational resources, and environmental factors.
* [https://www.cdc.gov/niosh/topics/mrsa/ National Institute for Occupational Safety and Health] information on the bacteria, exposure in the workplace, and reducing risks of being infected.

{{Gram-positive firmicutes diseases}}
{{Taxonbar|from=Q595158}}
{{Authority control}}

[[Category:Antibiotic-resistant bacteria]]
[[Category:Bacterial diseases]]
[[Category:Health care-associated infections]]
[[Category:Staphylococcaceae]]
[[Category:Staphylococcus|*]]
[[Category:Infection-related cutaneous conditions]]
[[Category:Bacterium-related cutaneous conditions]]
[[Category:Cat diseases]]
[[Category:Pathovars]]