Nasal colonization by Staphylococcus aureus in Health Sciences students and analysis of risk factors under a One Health perspective

Abstract

Background: Staphylococcus aureus is the leading bacterial cause of death globally [1]. Nasal carriage of S. aureus increases the risk of invasive infections, including by methicillin-resistant S. aureus (MRSA) strains, but studies including Portuguese university students (PUS) are scarce. Objective: To analyse the prevalence of methicillin-susceptible S. aureus (MSSA) and MRSA among PUS enrolled in different courses/years (1^st-4^th) at IUCS-CESPU, characterize their antibiotic resistance profiles, and assess the potential risk factors. Methods: Swabs collected during March-December 2022 from anterior nares of 156 volunteers (median 22-years) were processed in mannitol-salt agar and, in parallel, enriched in brain-heart broth with NaCl 6.5% further plated onto ChromID® MRSA SMART. Typical colonies were stored for species identification (MALDITOF-MS) and antibiotic susceptibility testing (disk diffusion; EUCAST/CLSI guidelines). Each student completed a questionnaire comprising demographic/clinical/social parameters. Statistical analysis was conducted in IBM-SPSS Statistics 26 using binary logistic regression applying a backward stepwise (likelihood ratio) method, with α=0.05, selecting variables using Chi-square tests and Mann-Whitney U tests for which p≤0.20, >10 occurrences, not biologically correlated [2]. Results: Prevalence of MSSA and MRSA (cefoxitin screening) were 28.8% and 1.9%, respectively. From the 45 positive samples, 9% were multidrug-resistant, 38% were resistant to penicillin, 40% to erythromycin, 40% to clindamycin (inducible), 7% to cefoxitin, 2% to tetracycline, and 2% to rifampicin. Self-reported frequent contact with animals (OR=3.44, CI 95%: 1.10–10.66) were positively associated with S. aureus, while regular sports participation presented a negative association (OR=0.36, CI 95%: 0.17–0.77). Sports participation was not correlated with self-reported excellent health (χ²=0.680, p=0.409). Conclusions: This is one of the first studies assessing MSSA/MRSA rates in PUS after the COVID-19 pandemics imposing higher self-protection/hygienization. While PUS-MSSA rates are similar to that previously observed, PUS-MRSA rates are slightly higher. Additional samples are being processed to explore future trends and other potential One Health factors influencing MSSA/MRSA colonization.