Objective To assess the prevalence and risk factors for S. aureus and methicillin-resistant S. aureus (MRSA) nasal colonization in Spanish children. Methods Cross-sectional study of patients <14 years from primary care centers all over Spain. Clinical data and nasal aspirates were collected from March to July 2018. Results A total of 1876 patients were enrolled. Prevalence of S. aureus and MRSA colonization were 33% (95% CI 30.9–35.1) and 1.44% (95% CI 0.9–2), respectively. Thirty-three percent of the children (633/1876) presented chronic conditions, mainly atopic dermatitis, asthma and/or allergy (524/633). Factors associated with S. aureus colonization were age ≥5 years (OR 1.10, 95% CI 1.07–1.12), male sex (OR 1.43, 95% CI 1.17–1.76), urban setting (OR 1.46, 95% CI 1.08–1.97) and the presence of asthma, atopic dermatitis or allergies (OR 1.25; 95% CI: 1.093–1.43). Rural residence was the only factor associated with MRSA colonization (OR 3.62, 95% CI 1.57–8.36). MRSA was more frequently resistant than methicillin-susceptible S. aureus to ciprofloxacin [41.2% vs 2.6%; p<0.0001], clindamycin [26% vs 16.9%; p=0.39], and mupirocin [14.3% vs 6.7%; p=0.18]. None of the MRSA strains was resistant to tetracycline, fosfomycin, vancomycin or daptomycin. Conclusions The main risk factors for S. aureus colonization in Spanish children are being above five years of age, male gender, atopic dermatitis, asthma or allergy, and residence in urban areas. MRSA colonization is low, but higher than in other European countries and is associated with rural settings.

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To assess drug-resistant bacterial colonisation rates and associated risk factors in children with complex chronic conditions admitted to a national reference unit in Spain. Cross-sectional study that included all children admitted to our unit from September 2018 to July 2019. Rectal swabs were obtained to determine multidrug-resistant Gram-negative bacilli (MR-GNB) colonisation, and nasal swab to determine S. aureus and methicillin-resistant S. aureus (MRSA) colonisation. Medical records were reviewed. 100 children were included, with a median of four complex chronic conditions. Sixteen percent had S. aureus colonisation, including two MRSA. S. aureus colonisation was associated with technology-dependent children, while being on antibiotic prophylaxis or having undergone antibiotic therapy in the previous month were protective factors. The prevalence of MR-GNB colonisation was 27%, which was associated with immunosuppressive therapy (aOR 31; 2.02–47]; p = 0.01), antibiotic prophylaxis (aOR 4.56; 1.4–14.86; p = 0.012), previously treated skin-infections (aOR 2.9; 1.07–8.14; p = 0.03), surgery in the previous year (aOR 1.4; 1.06–1.8; p = 0.014), and hospital admission in the previous year (aOR 1.79; [1.26–2.56]; p = 0.001). The rate of S. aureus nasal colonisation in this series was not high despite the presence of chronic conditions, and few cases corresponded to MRSA. Antibiotic prophylaxis, immunosuppressive therapies, history of infections, previous surgeries, and length of admission in the previous year were risk factors for MR-GNB colonisation.