genetic characteristics of ha-mrsa. community-acquired mrsa (ca-mrsa) strains emerged in late 1990 to 2000, infecting healthy people who had not been in contact with healthcare facilities. researchers suggest that ca-mrsa did not evolve from ha-mrsa. this is further proven by molecular typing of ca-mrsa strains and genome comparison between ca-mrsa and ha-mrsa, which indicate that novel mrsa strains integrated sccmec into mssa separately on its own. by mid-2000, ca-mrsa was introduced into healthcare systems and distinguishing ca-mrsa from ha-mrsa became a difficult process. community-acquired mrsa is more easily treated and more virulent than hospital-acquired mrsa (ha-mrsa). 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. in the united states, most cases of ca-mrsa are caused by a cc8 strain designated st8:usa300, which carries sccmec type iv, panton–valentine leukocidin, psm-alpha and enterotoxins q and k, and st1:usa400. 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. 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 sccmec type iv, predominate. 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. a mrsa strain, cc398, is found in intensively reared production animals (primarily pigs, but also cattle and poultry), where it can be transmitted to humans as la-mrsa (livestock-associated mrsa). diagnosis a selective and differential chromogenic medium for the qualitative direct detection of mrsa 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. 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 "strong suspicion" and techniques by the treating physician; these include quantitative pcr procedures, which are employed in clinical laboratories for quickly detecting and identifying mrsa strains. another common laboratory test is a rapid latex 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. 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 spores and it is not motile. it is frequently found in grape-like clusters or chains.: 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 a number of 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 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.: 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 suspectible 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.: 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 identifies carriers and reduces infection rates. it is especially important to test patients in these settings since 2% of people are carriers of mrsa, even though in many of these cases the bacteria reside in the nostril and the patient will not present any symptoms. 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 has been found to be effective in minimizing the spread of mrsa in hospitals in the united states, denmark, finland, and the netherlands. handwashing the centers for disease control and prevention offers suggestions for preventing the contraction and spread of mrsa infection which are applicable to those in community settings, including incarcerated populations, childcare center employees, and athletes. to prevent the spread of mrsa, the recommendations are to 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. isolation excluding medical facilities, current us guidance does not require workers with mrsa infections to be routinely excluded from the general workplace. 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, and patients with wound drainage should also automatically be put on "contact precaution," regardless of whether or not they have a known infection. workers with active infections are excluded from activities where skin-to-skin contact is likely to occur. 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 environmental protection agency-registered disinfectants. in hospital settings, contact isolation can be stopped after one to three cultures come back negative. 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. 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. restricting antibiotic use glycopeptides, cephalosporins, and in particular, quinolones are associated with an increased risk of colonisation of mrsa. reducing use of antibiotic classes that promote mrsa colonisation, especially fluoroquinolones, is recommended in current guidelines. 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 "search and destroy" 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 "search and destroy" strategy is overwhelmed. 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. decolonization main article: 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, and insufficient studies had been conducted to understand how to treat surgical wounds that had been colonized with mrsa. as of 2013, whether strategies to eradicate mrsa colonization of people in nursing homes reduced infection rates was not known. care should be taken when trying to drain boils, as disruption of surrounding tissue can lead to larger infections, including infection of the blood stream. mupirocin 2% ointment can be effective at reducing the size of lesions. a secondary covering of clothing is preferred. 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. community settings maintaining the necessary cleanliness may be difficult for people if they do not have access to facilities such as public toilets with handwashing facilities. in the united kingdom, the workplace (health, safety and welfare) regulations 1992 require businesses to provide toilets for their employees, along with washing facilities including soap or other suitable means of cleaning. guidance on how many toilets to provide and what sort of washing facilities should be provided alongside them is given in the workplace (health, safety and welfare) approved code of practice and guidance l24, available from health and safety executive books, but no legal obligations exist on local authorities in the united kingdom to provide public toilets, and although in 2008, the house of commons communities and local government committee called for a duty on local authorities to develop a public toilet strategy, this was rejected by the government. agriculture