Time-Series Analysis of Staphylococcus aureus and MRSA Trends, Seasonality, and Pandemic-Associated Disruptions in a Tertiary-Care University Hospital (2016–2025)

Background Methicillin-resistant Staphylococcus aureus (MRSA) remains a leading cause of healthcareassociated infections worldwide, yet longterm trends and the COVID-19 pandemic’s impact in Latin American hospitals are inadequately described. We aimed to characterize decadelong epidemiology, seasonal patterns, and pandemicassociated changes in hospitalonset S. aureus infections at a tertiarycare referral center. Methods We conducted a retrospective timeseries analysis of all clinically significant S. aureus isolates recovered from June 30, 2016 to March 29, 2025 at our university hospital. Weekly counts and proportions of MRSA were smoothed using LOESS (span = 0.3). Monotonic trends were evaluated via the Mann–Kendall test and Theil–Sen estimator. Seasonality was assessed with SeasonalTrend decomposition using Loess (STL), generalized additive models (GAMs) with cyclic splines, and Fourier spectral analysis. Interrupted timeseries (ITS) segmented regression estimated level and slope changes on March 1, 2020 (pandemic onset) and March 1, 2022 (postpeak stabilization). Results Among 6318 clinically significant S. aureus isolates, 1308 (21.7%) were MRSA. Proportion peaked at approximately 38% in late 2017 before undergoing a sustained decline to below 10% by June 2025 (median weekly Sen’s slope = − 0.00056; Mann–Kendall z = − 9.72, p < 0.001). ITS analysis of total S. aureus counts revealed an accelerated case incidence during the high SARS‑CoV‑2 circulation phase (March 1, 2020 – Feb 28, 2022), with a significant slope increase of + 0.0311 cases/week (SE 0.0086; p = 0.0003), yielding a net drift of + 0.0416 cases/week despite an initial level drop at pandemic onset. In contrast, segmented regression of MRSA counts showed no significant level change at the pandemic’s start (β₂ = − 3.490 cases; SE 4.048; p = 0.390) nor slope modification during high viral circulation (β₃ = − 0.018 cases/month; SE 0.2498; p = 0.943); instead, only the post‑peak stabilization period (from March 1, 2022) exhibited a statistically robust downward trend (β₅ = − 0.418 cases/month; SE 0.1528; p = 0.007). STL decomposition also revealed a stable 12‑month cycle, with consistent mid‑year peaks recurring annually between April and July. Conclusions Our decade‑long surveillance demonstrated a persistent, significant MRSA decline despite stable seasonal mid‑year peaks and a COVID‑19–associated surge in overall S. aureus cases without a parallel rise in resistance. Post‑pandemic, MRSA incidence decreased even more sharply. Elucidating these mechanisms via genomic epidemiology and multicenter studies will be essential to guide continuous, seasonally targeted interventions in similar settings.