High Staphylococcus aureus Colonization Prevalence among Patients with Skin and Soft Tissue Infections and Controls in an Urban Emergency Department

Abstract

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 ...

Staphylococcus aureus Colonization and Strain Type at Various Body Sites among Patients with a Closed Abscess and Uninfected Controls at U.S. Emergency Departments

“…The proportion of closed abscesses from which S. aureus was cultured (57.8%) and the proportions of infections due to MRSA and MSSA (33.3% and 24.5%, respectively) were similar in our study to those found in other recent U.S. studies (22,26,27) but were substantially lower than those found in previous studies conducted within this network of EDs, which found MRSA in 63% of patients presenting with an abscess (2). This might indicate that community-associated SSTI due to S. aureus is decreasing, perhaps due to increased awareness of this disease and more active measures to prevent infection in community settings.…”

“…In contrast, we found a higher rate of MRSA nasal carriage among control subjects (9.5%) than others have reported for subjects in the community (7,22,24) and those presenting to EDs with skin infections (22). MRSA nasal colonization in our study was much higher among cases (25.2%) than among controls (9.5%), a finding that has also been reported by others (22,25).…”

“…Since all of the case subjects in this study had closed skin infections, it is unlikely that the abscess was a source of colonization for other body sites. It is interesting that the rate of colonization with the infecting strain was higher in our study than in another recent study of patients presenting to EDs with a skin infection, in which both open and closed abscesses were examined (88.2% versus 58.4%) (22). This might suggest that S. aureus colonization precedes infection in community settings, as has been described for health care settings (4).…”

“…If one considers only the nares, MSSA colonization rates among case and control subjects were similar (27.9% and 29.3%, respectively), and these rates were comparable to those found in other studies of community subjects that did not include broth enrichment cultures (7). Of note, a recent study among patients presenting to a single ED found much lower rates of MSSA nasal colonization among case patients than we found, even with the use of broth enrichment (22). In contrast, we found a higher rate of MRSA nasal carriage among control subjects (9.5%) than others have reported for subjects in the community (7,22,24) and those presenting to EDs with skin infections (22).…”

“…However, if members of the population under surveillance have a skin infection, our data suggest that the groin would be the preferred single site for detecting MRSA colonization. Other recent studies have also implicated the groin and rectum as important sites of colonization with MRSA (22,23).…”