Cause:Staphylococcus aureus
Pathophys:Multiple exotoxins increase its pathogenicity including ß-lactamase, coagulase, hyaluronidase, other proteases, leukocidin, lipases, staphylokinase. Hair follicles infected because fibrin restrains spread but retards healing
Normal inhabitant of skin and upper respiratory track; 90% resistant to penicillin; 70% are now community-acquired MRSA (Ann IM 2006;144:309); C-MRSA increasing in significance in skin infections, supparative otitis media in kids
Sx:Pain, swelling, may have fever
Si:Abscesses, carbuncle, furuncle, pneumonia, and empyema; acute endocarditis involving healthy valves; osteomyelitis, usually metaphyseal; septicemia
DIC; endocarditis, including R-sided, esp in drug users; metastatic infections; necrotizing fasciitis (Nejm 2005;352:1445)
Lab:Bact:Gram-positive cocci clusters, coagulase-positive; methicillin resistance present in over 50% in some ICUs (Nejm 1998;339:520)
Rx:
Prevention: mupirocin (Bactroban) topical rx to anterior nares of carriers (30% of population) preop reduces nosocomial postop infection rates (Nejm 2002;346:1871,1905 vs Ann IM 2004;140:419). Chlorhexidine daily in patient baths with chlorhexidine/alcohol op site preparation together reduce high risk surgery wound infections × 50% (Nejm 2010;362:9, 18, 75)
Surgical drainage
ß-Lactamase–resistant drug like nafcillin/oxacillin iv, later go to po cloxacillin or diclox. Cephalosporin, clindamycin, Tm/S, erythromycin
of methicillin-resistant staph (MRSA), 2 types, but rapidly evolving epidemiology: community-acquired (Nejm 2006;355:653, 666, 724; 2005;352:1436, 1455, 1485), which often causes skin, soft tissue, and post-influenza pneumonia infections and is sensitive to quinolones, Tm/S (ii DS tab po bid), doxycycline, and clindamycin (beware clindamycin “sensitive” but really resistant if erythromycin resistant = “D test”); or hospital-acquired type where must use vancomycin w or w/o rifampin, but resistance appearing (Nejm 1999;340:493, 517); PLUS nasal mupiricin to eradicate carrier state
of vancomycin-resistant MRSA (Nejm 2003;348:1342): linezolid (Zyvox), or Synercid (quinupristin-dalfopristin), or daptomycin (not for pneumonia), or tigecycline, or dalbavancin
of recurrent abscesses: prevent w rifampin 600 mg bid × 5 d (Nejm 1986;315:91) + vancomycin or Tm/S (Ann IM 1982;97:317)
No consensus on treatment of infected orthopedic appliances; some approaches: pencillinase-resistant penicillin + rifampin × 2 wk then quinolone + rifampin f/u rx × 3-6 mo (Jama 1998;279:1537)