Integrated Hospital, Emergency Department, and Community Surveillance for Respiratory Viruses in Milan, Italy

Respiratory virus circulation may vary across healthcare settings and age groups, potentially limiting the interpretability of surveillance based on a single source. In Milan, Italy, established community- and emergency department-based systems coexist with hospital laboratory testing, but hospital ward-level data are not routinely integrated. The aims of this study were to describe respiratory viruses' epidemiology and assess whether ward-based surveillance complements community and ED surveillance. We analyzed molecular test results from respiratory samples collected from January 1, 2024 (W1/2024) to October 12, 2025 (W41/2025) in community, ED, and hospital ward settings. Viruses included influenza A (IAV), influenza B (IBV), RSV, and SARS-CoV-2 (with extended panels in a subset). Among 8029 samples, overall positivity for ≥ 1 virus was 46.8%, highest in ED (51.1%) and community (50.5%) and lower in wards (36.7%) (p < 0.001). During 2024-2025, IAV was first detected in wards (W33/2024) and peaked earlier in wards (W2/2025) than community (W3/2025) and ED (W4/2025). IBV was first detected in ED (W36/2024) and peaked in ED (W5/2025), community (W7/2025), and wards (W8/2025). RSV reappeared first in community (W37/2024) and peaked in community/ED (W50/2024) and later in wards (W2/2025). Respiratory virus positivity and descriptive peak timing differed across healthcare settings and age groups. Ward-based surveillance provided complementary information for hospitalized and older populations, but it was not consistently earlier or superior to community or ED surveillance. Integrated, multi-setting surveillance can improve situational awareness when interpreted alongside differences in tested populations, testing indications, and clinical outcome availability.