Large screening of CA-MRSA among Staphylococcus aureus colonizing healthy young children living in two areas (urban and rural) of Portugal

<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background</jats:title> <jats:p>The incidence of pediatric infections due to community-associated methicillin-resistant <jats:italic>Staphylococcus aureus</jats:italic> (CA-MRSA), including children with no identifiable risk factors, has increased worldwide in the last decade. This suggests that healthy children may constitute a reservoir of MRSA in the community. In this study, nested within a larger one on nasopharyngeal ecology, we aimed to: (i) evaluate the prevalence of MRSA colonizing young children in Portugal; and (ii) compare results with those obtained in a study conducted a decade ago, when this prevalence was <0.5%.</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>In the years 2006, 2007, and 2009, nasopharyngeal samples were obtained from 2,100 children aged up to 6 years attending day-care centers. <jats:italic>S. aureus</jats:italic> were isolated by routine procedures and strains were tested for susceptibility against a panel of 12 antimicrobial agents. MRSA isolates were further characterized by SmaI-PFGE profiling, MLST, <jats:italic>spa</jats:italic> typing, SCC<jats:italic>mec</jats:italic> typing, and presence of virulence factors.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Seventeen percent of the children carried <jats:italic>S. aureus</jats:italic>. Among the 365 isolates, non-susceptibility rates were 88% to penicillin, 14% to erythromycin, 6% to clindamycin, 2% to tetracycline, and <1% to oxacillin, rifampicin, ciprofloxacin, and SXT. Three MRSA strains were isolated. These had properties of CA-MRSA, such as low-level resistance to oxacillin and limited resistance to non-beta-lactams. Two CA-MRSA were related to USA700 (ST72-IV): one was ST72-IVc, <jats:italic>spa</jats:italic> type t148; the other was ST939-IVa (ST939 is a single locus variant (SLV) of ST72), <jats:italic>spa</jats:italic> type t324. The third strain was related to USA300 (ST8-IV) being characterized by ST931 (SLV of ST8)-VI, <jats:italic>spa</jats:italic> type t008. The three MRSA strains were PVL-negative, but all carried LukE-LukD leukocidin, hemolysins gamma, gamma variant and beta, and staphylococcal enterotoxin <jats:italic>sel</jats:italic>.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Our results, based on analysis of <jats:italic>S. aureus</jats:italic> isolated from nasopharyngeal samples, suggest that in Portugal the prevalence of CA-MRSA carriage in healthy young children remains extremely low favoring the exclusion of this group as a reservoir of such isolates.</jats:p> </jats:sec>