Risk Factors, Length of Stay and In-Hospital Mortality of Methicillin-Resistant Staphylococcus aureus Infections: A Case-Control Study

Introduction: The emergence of strains of methicillin-resistant Staphylococcus aureus is a serious therapeutic challenge in healthcare provision. With this study, we aimed to investigate the risk factors and clinical outcomes (mortality and length of hospital stay) associated with methicillin-resistant Staphylococcus aureus infections in patients admitted to a district hospital in Portugal. Material and Methods: A case-control study was performed in 96 cases and 122 controls, selected, respectively, as function of antibiotic resistance or sensitivity to methicillin. Data were obtained through consultation of clinical records and subjected to multivariate statistical analysis. Results: We identified the following independent risk factors for the occurrence of methicillin-resistant Staphylococcus aureus infection: urinary catheter (aOR = 10.62, 95% CI 3.66 - 30.78), prior use of antibiotics in the last 30 days (aOR = 5.60, 95% CI 2.15 - 14.62), exposure to 5 - 7 days of hospitalization (aOR = 4.99, 95% CI 1.20 - 20.79) or to >= 8 days (aOR = 5.34, 95% CI 1.18 - 24.22), chronic obstructive pulmonary disease (aOR = 4.27, 95% CI 1.64 - 11.13) and recent hospitalization (aOR = 2.66, 95% CI 1.14 - 6.23). Compared to infections due to methicillin-susceptible Staphylococcus aureus, we found increased probability of having a longer hospital stay (aHR = 1.74, 95% CI 1.11 - 2.71) and in-hospital mortality was significantly higher (p = 0.001) between patients infected by methicillin-resistant Staphylococcus aureus. Discussion: The results demonstrate that methicillin resistance is associated with an increased clinical risk to patients infected by Staphylococcus aureus, in particular, a raised mortality and prolonged hospitalization. Conclusion: Our study underlines the additional burden imposed by methicillin resistance in Staphylococcus aureus infections. This highlights an urgent need to reinforce and optimize prevention, control, timely detection and effective treatment strategies for multidrug-resistant Staphylococcus aureus strains.