Background. The USA300 methicillin resistant Staphylococcus aureus (MRSA) genetic background has rapidly emerged as the predominant cause of community-associated S. aureus infections in the U.S. However, epidemiologic characteristics of S. aureus household transmission are poorly understood.Methods. We performed a cross-sectional study of adults and children with S. aureus skin infections and their household contacts in Los Angeles and Chicago. Subjects were surveyed for S. aureus colonization of the nares, oropharynx, and inguinal region and risk factors for S. aureus disease. All isolates underwent genetic typing.Results. We enrolled 1162 persons (350 index patients and 812 household members). The most common infection isolate characteristic was ST8/SCCmec IV, PVL1 MRSA (USA300) (53%). S. aureus colonized 40% (137/350) of index patients and 50% (405/812) of household contacts. A nares-only survey would have missed 48% of S. aureus and 51% of MRSA colonized persons. Sixty-five percent of households had .1 S. aureus genetic background identified and 26% of MRSA isolates in household contacts were discordant with the index patients' infecting MRSA strain type. Factors independently associated (P , .05) with the index strain type colonizing household contacts were recent skin infection, recent cephalexin use, and USA300 genetic background.Conclusions. In our study population, USA300 MRSA appeared more transmissible among household members compared with other S. aureus genetic backgrounds. Strain distribution was complex; .1 S. aureus genetic background was present in many households. S. aureus decolonization strategies may need to address extra-nasal colonization and the consequences of eradicating S. aureus genetic backgrounds infrequently associated with infection.
As compared with incision and drainage alone, clindamycin or TMP-SMX in conjunction with incision and drainage improves short-term outcomes in patients who have a simple abscess. This benefit must be weighed against the known side-effect profile of these antimicrobials. (Funded by the National Institutes of Health; ClinicalTrials.gov number, NCT00730028 .).
The surface capsular polysaccharide (CP) is a virulence factor that has been used as an antigen in several successful vaccines against bacterial pathogens. A vaccine has not yet been licensed against Staphylococcus aureus, although two multicomponent vaccines that contain CP antigens are in clinical trials. In this study, we evaluated CP production in USA300 methicillin-resistant S. aureus (MRSA) isolates that have become the predominant community-associated MRSA clones in the United States. We found that all 167 USA300 MRSA and 50 USA300 methicillin-susceptible S. aureus (MSSA) isolates were CP negative (CP−). Moreover, all 16 USA500 isolates, which have been postulated to be the progenitor lineage of USA300, were also CP−. Whole-genome sequence analysis of 146 CP− USA300 MRSA isolates revealed they all carry a cap5 locus with 4 conserved mutations compared with strain Newman. Genetic complementation experiments revealed that three of these mutations (in the cap5 promoter, cap5D nucleotide 994, and cap5E nucleotide 223) ablated CP production in USA300 and that Cap5E75 Asp, located in the coenzyme-binding domain, is essential for capsule production. All but three USA300 MSSA isolates had the same four cap5 mutations found in USA300 MRSA isolates. Most isolates with a USA500 pulsotype carried three of these four USA300-specific mutations, suggesting the fourth mutation occurred in the USA300 lineage. Phylogenetic analysis of the cap loci of our USA300 isolates as well as publicly available genomes from 41 other sequence types revealed that the USA300-specific cap5 mutations arose sequentially in S. aureus in a common ancestor of USA300 and USA500 isolates.
In our longitudinal study, patients with a S. aureus skin infection were more likely to suffer a recurrence if household fomites were MRSA contaminated. Interventions to prevent recurrence may be enhanced by decontamination of household fomites.
Staphylococcus aureus is a commensal species that can also be a formidable pathogen. In the United States, an epidemic of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections has been occurring for the last 15 years. In the context of a study in which we identified patients with skin and soft tissue infections (SSTIs) and randomized them to receive one of two antimicrobial treatment regimens, we assessed S. aureus colonization in the nares, throat, and perianal skin on the day of enrollment and 40 days after therapy. We compared the prevalence of colonization between the SSTI patients and an uninfected control population. A total of 144 subjects and 130 controls, predominantly African American, participated in this study, and 116 returned for a 40-day follow-up visit. Of the SSTI patients, 76% were colonized with S. aureus at enrollment, as were 65% of the controls. Patients were more likely than the controls to be colonized with USA300 MRSA (62/144 [43.1%] versus 11/130 [8.5%], respectively; P < 0.001). The nares were not the most common site of colonization. The colonization prevalence diminished somewhat after antibiotic treatment but remained high. The isolates that colonized the controls were more likely than those in the patients to be methicillin-susceptible S. aureus (MSSA) (74/84 [88.1%] versus 56/106 [52.8%], respectively; P < 0.001). In conclusion, the prevalence of S. aureus colonization among SSTI patients was high and often involved USA300 MRSA. The prevalence diminished somewhat with antimicrobial therapy but remained high at the 40-day follow-up visit. Control subjects were also colonized at a high prevalence but most often with a genetic background not associated with a clinical infection in this study. S. aureus is a commensal species and a pathogen. Plans for decolonization or eradication should take this distinction into account. Staphylococcus aureus is a commensal species that can be a formidable pathogen. It has been traditionally held that the primary site of colonization with the species is the nasopharynx (1) and repeatedly documented that 25% to 40% of the population is colonized in the nasopharynx by S. aureus. Colonization is asymptomatic, but colonized individuals may develop an active infection and do so more frequently than uncolonized individuals (2). The pathophysiological processes that result in infection among colonized individuals are poorly understood.Recently, the notion that the nasopharynx is the primary site of colonization has been challenged by the finding of a higher prevalence of colonization at other body sites, notably the oropharynx and even the inguinal area (3, 4). Indeed, many individuals with colonization in the throat or on the skin over the inguinal area have no colonization in the nasopharynx (5-8). Small studies in the United States and elsewhere have demonstrated that S. aureus, and specifically the methicillin-resistant S. aureus (MRSA) genetic background USA300 can be found elsewhere on the body (reviewed in reference 4).In ...
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