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methicillin-resistant Staphylococcus aureus (MRSA)

Etiology: 1) unnecessary antibiotic use in general 2) antibiotics in food 3) bacterial mutation 4) risk factors for nosocomial infection: a) current or recent hospitalization treated with parenteral antibiotics b) residing in a long-term care facility c) invasive procedures d) recent or long-term antibiotic use e) prior infection with influenza ? [36] f) prior respiratory isolation of MRSA g) critically ill 5) risk factors for community-acquired infection a) young age - incomplete development of immune system b) participation in contact sports c) sharing towels or athletic equipment d) immunosuppression (AIDS) e) incarceration, crowded or unsanitary conditions f) end-stage renal disease g) injection drug use [30] 6) compared with MRSA carriers, risk of MRSA infection are 14 times lower for uncolonized patients & 125 times lower for MSSA carriers [29] Epidemiology: 1) healthcare-associated infection (80%) [12] 2) nursing homes - SCCmec II strains (hospital associated) 73% SCCmec IV strains (community-acquired) 8% [10] - foley catheter associated with groin or perianal colonization with MRSA [10] 3) outpatients a) 60% of community-acquired Staphylococcus in parts of Alaska, California, Georgia & Texas) [3] b) most outpatient infections involve skin & soft tissue [5,9] c) 70% of staphylococcal skin infections due to MRSA [7,9] d) healthcare-associated infection accounts for 76% of outpatient MRSA [12] 4) inpatients: a) 51% of MRSA+ patients at discharge clear MRSA within 1 year b) mean time to clearance 246 days 4) asymptomatic carriers - risk factors a) smokers b) insulin-requiring diabetes mellitus c) hemodialysis d) injection drug users 5) transmission is by contact 6) 17% overall decrease in community-onset & a 28% overall decrease in hospital-onset healthcare-associated infections between 2005 & 2008 [12] 7) decrease in MRSA between 2005 & 2011 [18] a) invasive nosocomial MRSA: 54% b) healthcare-associated community-onset MRSA: 28% Pathology: 1) skin infections & soft tissue infections (most common) [1] 2) pneumonia 3) resistance due to alterations in penicillin-binding protein(s) 4) virulence may be related to Panton-Valentine leukocidin Genetics: 1) 99% of isolates from single clone 'USA 300' [7] 1% of isolates from 'USA 400' 2) CA strains ? Laboratory: - D-test identifies erythromycin resistance with inducible resistance to clindamycin [6] - PCR provides rapid testing for MRSA [11] - methicillin resistance gene - MRSA nucleic acid - MRSA DNA - Staphylococcus aureus + MRSA nucleic acid - MRSA identified in isolate - methicillin resistant Staphylococcus aureus culture - blood cultures for bacteremia, sepsis - repeat every 2-4 days until negative - median time to clearance of MRSA is 7-9 days Special laboratory: - transthoracic echocardiogram (TTE) - transesophageal echocardiogram if TTE negative Radiology: - CT of abdomen & pelvis if transesophageal echocardiogram negative - MRI of spine rule out/in spinal epidural abscess if back pain - FDG PET-CT if no diagnosis - tagged leukocyte nuclear scan a late option Complications: - long-term carrier state in 20% of patients [24] Management: 1) abscess - incision & drainage [1] 2) pharmaceutical agents [13] a) consider resistant to all beta-lactam antibiotics b) may also be resistant to macrolides, fluoroquinolones, Bactrim, clindamycin, aminoglycosides c) nosocomial infection or patients requiring hospitalization: 1] multidrug-resistance common [3] 2] IV vancomycin [3,7] or daptomycin for MRSA sepsis - therapy for >= 14 days - 4-6 weeks of therapy for MRSA sepsis in a patient with arthroplasty [37] - median time to clearance of MRSA bacteremia is 7-9 days [1] - adding beta-lactam to vancomycin or daptomycin for MRSA sepsis of no benefit [34] 3] linezolid useful as oral agent a] may have advantage over vancomycin [17] b] not indicated for treatment of MRSA endocarditis or sepsis [1] 4] trimethoprim/sulfamethoxazole plus rifampicin noninferior to linezolid [22] 5] trimethoprim/sulfamethoxazole inferior to vancomycin especially for sepsis [25] 6] ceftaroline (5th generation cephalosporin) IV d) ouptatient: (skin infections) - Bactrim, doxycycline, minocycline, or clindamycin [3] - 2 Bactrim DS or Septra DS PO BID-TID [6] - clindamycin may diminish duration of carrier state after resolution of index infection relative to trimethoprim/sulfamethoxazole [24] e) vancomycin resistance [14]; MIC > 2 ug/mL - daptomycin 10 mg/kg/day plus a second agent such as gentamicin, rifampin, linezolid, TMP-SMX, or a beta-lactam antibiotic - do not use daptomycin for staphylococcal pneumonia (inactivated by surfactant) - quinupristin-dalfopristin, TMP-SMX, linezolid, or telavancin alone or in combination for daptomycin resistance [2,13] - fosfomycin has activity against MRSA & VRE [1] 3) carrier state a) eradication of carrier state with mupirocin (Bactroban) to anterior nares (of nose), fingernails & to wounds [9] - twice-monthly decolonization with mupirocin for 6 months reduces post hospital discharge MRSA infections [33] - apparently MRSA resistance develops b) chlorhexidine (Hibiclens) baths [3] c) mupirocin, chlorhexidine, & bleach-water can temporarily eradicate Staphylococcus aureus colonization [16] d) do NOT treat carrier state with systemic agents e) hot coffee &/or tea reduces risk of MRSA nasal carriage by ~ 50% [15] 4) bleach baths may be of benefit for recurrent Staphyloccus infection (MRSA or MSSA) [20] 5) infection control; contact precautions [28] a) handwashing & barrier techniques to prevent transmission - alcohol-based hand sanitizer effective b) maintain contact precautions in patients not receiving an antibiotic active against MRSA until 1-3 negative cultures obtained [27] c) isolation of patients with MRSA to prevent outbreaks [4] d) isolation precautions not needed in communities where MRSA is endemic [23]

Interactions

disease interactions

Related

nosocomial infection; nursing home acquired infection penicillin binding protein

General

Staphylococcus aureus

References

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