Positive cx or test from nares (MRSA screening) = colonization, not an infection.Dx: positive cx from a sterile site (blood, joint, CSF), abscess or wound.
Osteoarticular infections (osteomyelitis, septic arthritis).Pneumonia: especially suspect with influenza-associated infection.Probably not a frequent cause of cellulitis in the absence of purulence (abscess) or wound, as uncomplicated cellulitis is mostly streptococcal in origin.Rarely, serious disease with or necrotizing fasciitis may occur.Most skin/soft tissue infections are relatively benign with a good response to I&D ± antibiotics, although recurrent infections can occur in some.
#GRAM POSITIVE COCCI IN CLUSTERS SKIN#
MRSA has been traditionally associated w/ healthcare system interaction CA-MRSA has emerged as a significant pathogen in the 1990s, especially in children, prisoners, IDUs (although rates were also increased in adults with no clear risk factors).Methicillin resistance is now common in both community and many hospital settings in North America (much less in some Northern European countries).Risk factors: skin disease, venous catheters, other foreign bodies (e.g., prosthetic joints, pacemakers), IDU, hemodialysis, recent surgical procedure.Carriers have a greater risk of subsequent infection.Higher carriage rates are seen in some populations, e.g., diabetics, injection drug users (IDU), HIV or dialysis patients.Carried normally in anterior nares by 20-30% of the U.S.VISA, VRSA: vancomycin resistance remains rare, and is seen mostly in patients with long-term vancomycin therapy (e.g., ulcers in diabetic dialysis patients).If the isolate is erythromycin-resistant, must confirm clindamycin susceptibility with D-test. Clindamycin susceptibilities vary geographically.Community-acquired MRSA (CA-MRSA) isolates (less noted now as MSSA and MRSA now nearly equivalent in many hospitals/communities): often maintain susceptibility to tetracyclines ( tetracycline, doxycycline, minocycline, tigecycline) and TMP/SMX.Methicillin resistance (MRSA) is conferred by the presence of the mecA gene that encodes penicillin-binding protein 2a, an enzyme that has a low affinity for beta-lactams and thus leads to resistance to methicillin, oxacillin, nafcillin, and cephalosporins.Use of penicillin Vk or G for serious infections discouraged as the reliability of PCN susceptibility is questionable without detailed testing suggest using agents typically employed for MSSA.Penicillin resistance (MSSA) is conferred by penicillinase production, which can be overcome by the addition of a beta-lactamase inhibitor (e.g., amoxicillin/clavulanate, ampicillin/sulbactam) or use of penicillinase-resistant penicillins (e.g., oxacillin, nafcillin).Antimicrobial resistance: rare isolates remain penicillin-susceptible.Chromogenic methods (sensitivity > 99%).Direct tube coagulase test (65 to 84.1% sensitivity and 98.7 to 100% specificity).Enzyme-based tests, (90.5 to 100% sensitivity and 96.6 to 100% specificity).mec A, SCCmec cassette, orfX gene (SCCmec-orfX).PCR (93.8 to 100% sensitivity and 98.6 to 100% specificity), multiple methods.Fluorescence in situ hybridization (85 to 100% sensitivity and 100% specificity).Rapid identification methods, numerous (not a complete list below):.Blood agar with a novobiocin (NB) disc: creamy, gold colonies β-hemolysis, novobiocin sensitive.aureus: coagulase-positive and thermonuclease positive. Easily grown on blood agar or other conventional media.Aerobic, Gram-positive cocci, usually seen in clusters.
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