MRSA transmission in hospitals across Alberta, Canada: a comparative study combining unidentified colonized cases upon admission

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is a prevalent bacterium in medical settings. It can result in bloodstream infections and other severe illnesses, and patients may have a high risk of dying from these conditions. This study aimed to examine MRSA transmission in hospitals across Alberta and how undetected colonized patients on admission affect MRSA spread. METHODS: We used a Bayesian compartmental model to simulate MRSA spread across 106 acute care hospitals in Alberta. The model assumes that MRSA spreads through interactions between susceptible individuals and MRSA patients, including both hospital-acquired (HA) and community-acquired (CA) MRSA cases. Data from Edmonton, Calgary, rural Alberta and all regions in Alberta were used to fit the model. We also assumed that a small percentage of patients were colonized upon admission but were not promptly identified in hospitals, and we tested the model assumptions. Transmission rates were estimated using a Bayesian framework with Markov chain Monte Carlo (MCMC) algorithms. We compared transmission rates across several regions in Alberta and assessed the effect of MRSA prevalence at hospital admission on MRSA transmission. RESULTS: When the model fit the data in hospitals in all areas of Alberta, the average number of susceptible people colonized due to patients with HA-MRSA colonization, patients with HA-MRSA infections, patients with CA-MRSA colonization, and patients with CA-MRSA infections per contact per month are around 0.03 (95% CI: (0.001, 0.101)), 0.08 (95% CI: (0.002, 0.278)), 0.01 (95% CI: (0.000, 0.033)) and 0.05 (95% CI: (0.001, 0.182)), respectively. Assuming 0.8 colonized cases per 1000 admissions, the average number of susceptible people who become colonized due to patients with HA-MRSA infections per contact per month in Edmonton, Calgary and rural hospitals are 0.05 (95% CI: (0.001, 0.174)), 0.43 (95% CI: (0.018, 1.152)) and 0.22 (95% CI: (0.007, 0.722)), respectively. Assuming more unidentified colonized cases in hospitals, transmission rates between susceptible people and infected patients increase marginally. CONCLUSION: MRSA transmission rates appear to be marginally higher in Calgary hospitals compared to Edmonton, and rural hospitals seem to have lower transmission rates than in Calgary but higher than in Edmonton, with 95% credible intervals (CIs) overlapping. Our model also suggests that infected patients have a higher probability of transmitting MRSA to susceptible people in most Alberta hospitals.