Prevalence, incidence burden, and clinical impact of healthcare-associated infections and antimicrobial resistance: a national prevalent cohort study in acute care hospitals in Greece Evangelos I Kritsotakis,1 Flora Kontopidou,2 Eirini Astrinaki,3 Maria Roumbelaki,4 Eleni Ioannidou,5 Achilles Gikas6 1School of Health and Related Research, Faculty of Medicine, Dentistry and Health, University of Sheffield, Sheffield, UK; 2Healthcare Associated Infections and Antimicrobial Resistance Office, Hellenic Center for Disease Control and Prevention, Athens, 3Infection Control Committee, University Hospital of Heraklion, 4Department of Nursing, Technological Educational Institute of Crete, Heraklion, 5Department of Internal Medicine, Rethymnon General Hospital, Rethymnon, 6Department of Internal Medicine and Infectious Diseases, University Hospital of Heraklion, Heraklion, Greece Background: Assessing the overall burden of healthcare-associated infections (HAIs) is challenging, but imperative in evaluating the cost-effectiveness of infection control programs. This study aimed to estimate the point prevalence and annual incidence of HAIs in Greece and assess the excess length of stay (LOS) and mortality attributable to HAIs, overall and for main infection sites and tracer antimicrobial resistance (AMR) phenotypes and pathogens.Patients and methods: This prevalent cohort study used a nationally representative cross-section of 8,247 inpatients in 37 acute care hospitals to record active HAIs of all types at baseline and overall LOS and in-hospital mortality up to 90 days following hospital admission. HAI incidence was estimated using prevalence-to-incidence conversion methods. Excess mortality and LOS were assessed by Cox regression and multistate models correcting for confounding and time-dependent biases.Results: HAIs were encountered with daily prevalence of 9.1% (95% confidence interval [CI] 7.8%–10.6%). The estimated annual HAI incidence was 5.2% (95% CI 4.4%–5.3%), corresponding to approximately 121,000 (95% CI 103,500–123,700) affected patients each year in the country. Ninety-day mortality risk was increased by 80% in patients with HAI compared to those without HAI (adjusted hazard ratio 1.8; 95% CI 1.3–2.6). Lower respiratory tract infections, bloodstream infections, and multiple concurrent HAIs doubled the risk of death, whereas surgical site and urinary tract infections were not associated with increased mortality. AMR had significant impact on the daily risk of 90-day mortality, which was increased by 90%–110% in patients infected by carbapenem-resistant gram-negative pathogens. HAIs increased LOS for an average of 4.3 (95% CI 2.4–6.2) additional days. Mean excess LOS exceeded 20 days in infections caused by major carbapenem-resistant gram-negative pathogens.Conclusion: HAIs, alongside with increasing AMR, pose significant burden to the hospital system. Burden estimates obtained in this study will be valuable in future evaluations of infection prevention programs.Keywords: nosocomial infections, antibiotic resistance, length of stay, mortality, prevalence, incidence