Nasal carriage of Staphylococcus aureus in Botucatu, Brazil: a population-based survey.

Recent increases in the incidence and severity of staphylococcal infections renewed interest in studies that assess the burden of asymptomatic carriage of Staphylococcus aureus in the community setting. We conducted a population-based survey in the city of Botucatu, Brazil (122,000 inhabitants), in order to identify the prevalence of nasal carriage of Staphylococcus aureus (including methicillin-resistant strains). Nasal swabs were obtained from 686 persons over one year of age. Resistance to methicillin was assessed through phenotypic methods, identification of the mecA gene and typing of the Staphylococcal Chromosome Cassette mec (SCCmec). Methicillin-resistant S. aureus (MRSA) isolates were characterized using Pulsed-Field Gel Electrophoresis (PFGE), Multilocus Sequence Typing (MLST) and spa typing. Polymerase chain reaction was applied to identify genes coding for Panton-Valentine Leukocidin (PVL) in isolates. The prevalence of overall S. aureus carriage was 32.7% (95%CI, 29.2%-36.2%). Carriers were significantly younger (mean age, 28.1 versus 36.3 for non-carriers; OR for age, 0.98; 95%CI, 0.97-0.99) and likely to report recent skin infection (OR, 1.85; 95%CI, 1.03-3.34). Carriage of methicillin-resistant S. aureus (MRSA) was found in 0.9% of study subjects (95%CI, 0.4%-1.8%). All MRSA isolates harbored SCCmec type IV, and belonged to spa types t002 or t021, but none among them harbored genes coding for PLV. In MLST, most isolates belonged to clones ST5 or ST1776. However, we found one subject who carried a novel clone, ST2594. Two out of six MRSA carriers had household contacts colonized with isolates similar to theirs. Our study pointed to dissemination of community-associated MRSA among the Brazilian population.