ABSTRACT
BACKGROUND: The so-called community-associated methicillin-resistant Staphylococcus aureus (MRSA) strains are more frequently susceptible to non-ss-lactam antibiotics (including clindamycin) than health care-associated MRSA strains. We assessed whether predictive clinical characteristics of presumptive MRSA infections can be identified to guide choice of empiric antibiotic therapy. METHODS: A clinical syndrome was assigned to each inpatient and outpatient at the University of Chicago Medical Center with an MRSA infection in 2004 to 2005. Antimicrobial susceptibilities and molecular characteristics of MRSA isolates were assessed. Patients were stratified by lesion characteristics. RESULTS: Of MRSA isolates from 262 patients with purulent skin and soft tissue infections (SSTIs), 231 (88%) were susceptible to clindamycin, 253 (97%) contained staphylococcal chromosomal cassette mec (SCCmec) IV, and 245 (94%) contained Panton-Valentine leukocidin (pvl) genes, characteristics associated with community-associated MRSA strains. The presence of a purulent SSTI had a positive predictive value of 88% for a clindamycin-susceptible MRSA isolate. Among 87 isolates from a nonpurulent SSTI, 44% were susceptible to clindamycin and 34% contained pvl genes. In 179 invasive MRSA disease isolates, 33% were clindamycin-susceptible and 26% carried pvl genes. CONCLUSIONS: A purulent MRSA SSTI strongly predicted the presence of a clindamycin-susceptible MRSA isolate. Presence of the pvl genes was almost universal among MRSA isolates causing purulent SSTIs; this was less common in nonpurulent SSTIs and other clinical syndromes.
Subject(s)
Anti-Bacterial Agents/therapeutic use , Clindamycin/therapeutic use , Drug Resistance, Bacterial , Methicillin-Resistant Staphylococcus aureus , Staphylococcal Skin Infections/microbiology , Adult , Child , Humans , Predictive Value of Tests , Retrospective Studies , Staphylococcal Skin Infections/drug therapy , Suppuration/microbiologyABSTRACT
BACKGROUND: A community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has been defined as an MRSA infection in a patient who lacks specific risk factors for healthcare exposure. We sought to determine whether the absence or presence of these risk factors still predicts the phenotypic or genotypic characteristics of MRSA strains. METHODS: All clinical MRSA isolates were prospectively collected at the University of Chicago Hospitals from July 2004 through June 2005. Patients were interviewed and/or their medical records were reviewed. Isolates underwent genotyping and susceptibility testing. Data on patients and isolates were stratified in accordance with 8 frequently cited criteria for the identification of CA-MRSA and compared for concordance. RESULTS: Among 616 unique patients from whom MRSA isolates were recovered, 404 (65.6%) had risk factors for healthcare exposure. Of the 404 isolates recovered from these patients, 166 (41.1%) were clindamycin susceptible, 190 (47.0%) carried staphylococcal cassette chromosome mec (SCCmec) type IV, 145 (35.9%) carried the Panton-Valentine leukocidin genes (PVL+), and 162 (40.1%) were identified as sequence type (ST) 8 by multilocus sequence typing (MLST), all of which are characteristics commonly attributed to CA-MRSA strains. CONCLUSIONS: Association with the healthcare environment now has little predictive value for distinguishing patients with infection due to multidrug resistant MRSA isolates from those infected by CA-MRSA isolates, that is, isolates that are clindamycin-susceptible, PVL+, ST8, and/or contain SCCmec type IV. Defining CA-MRSA by the absence of risk factors for healthcare exposure greatly underestimates the burden of epidemic CA-MRSA disease.