Evaluation of the simplicity, representativeness, data completeness and timeliness of the national surveillance system for invasive Haemophilus influenzae disease in Italy, 2016–2023

The Italian National Surveillance System (NSS) for vaccine-preventable invasive bacterial diseases has monitored invasive Haemophilus influenzae disease (HID) since 2007; however, apart from a sensitivity analysis conducted in 2016, it has not undergone a comprehensive evaluation. This study assessed the simplicity, representativeness, timeliness, and data completeness of the HID NSS in Italy from 2016 to 2023. System simplicity was evaluated by examining the surveillance structure and reporting procedures. Representativeness was assessed by comparing the age, sex, and regional distribution of cases reported to the NSS with those recorded in hospital discharge registries. Data completeness was measured as the proportion of missing values across seventeen key variables, and timeliness as the interval between symptom onset and notification at the national level. During the study period, 1,286 cases were reported. Although the reporting structure was well defined, multiple stakeholders and regional variability complicated notification and data integration. Comparisons with hospital discharge records showed similar age-specific patterns but discrepancies in sex and regional distributions, with three regions reporting no cases. Data completeness ranged from 25 to 100% across variables and from 71 to 94% across regions, with vaccination status, outcome, and microbiological characterization variables showing the lowest completeness. Reporting timeliness improved nationally (median 7 days, IQR 3–20), although regional variation persisted. Overall, the NSS showed improvements in timeliness and completeness over time; however, regional heterogeneity remains, and integration of epidemiological and microbiological data remains a labor-intensive step in the surveillance workflow.