Prevalence and determinants of infection risk in hospitalised adults: a multicentre cross-sectional study using a structured risk assessment tool.

Background: Healthcare-associated infections remain a major public health challenge, contributing to increased morbidity, mortality, length of hospital stays, and healthcare costs. Systematic assessment of infection risk is essential to support preventive strategies and improve patient safety however remains insufficiently structured in many clinical settings. Objective: To estimate the prevalence of infection risk among hospitalised adults and to identify intrinsic and extrinsic factors associated with high infection risk using a structured risk assessment instrument. Methods: A multicentre, observational, cross-sectional study was conducted in adult inpatient wards across multiple Local Health Units of the Portuguese National Health Service during 2025. Infection risk was assessed using the Risk Assessment for Infection (RAC) scale, which evaluates intrinsic and extrinsic risk factors. Risk stratification was performed using complementary approaches, including receiver operating characteristics (ROC) analysis and percentile-based classification. The study was conducted in accordance with ethical requirements. Results: A total of 1,092 hospitalised adults were included. Most participants were classified as having moderate (53.6%) or high (11.4%) infection risk according to percentile-based stratification. Higher risk levels were significantly associated with intrinsic factors such as older age, multimorbidity, impaired tissue integrity, and reduced mobility, as well as extrinsic factors including previous hospitalisation, intra- or inter-hospital transfer, prolonged length of stay, invasive procedures, and pharmacological therapy. ROC analysis identified a cut-off point with good discriminative performance, while percentile-based stratification enabled a more granular three-level risk classification. Patients hospitalised in medical wards had significantly higher risk scores compared with those in surgical wards. Conclusion: This study demonstrates a high prevalence of infection risk among hospitalised adults and confirms the multifactorial nature of infection risk in hospital settings. The RAC scale proved to be a useful tool for systematic risk stratification, with the three-level classification providing enhanced clinical applicability. Integrating structured infection risk assessment into routine care may support early identification of high-risk patients, enable targeted preventive interventions, and strengthen infection prevention and control programmes.