Length of Stay and Comorbidities in Patients Hospitalized for Herpes Zoster: A Real-World Italian Study (2011–2023)

Abstract

Introduction
Herpes zoster (HZ) represents a significant public health burden and a frequent cause of hospital admission, especially among elderly and clinically vulnerable individuals. While the disease is generally self-limiting, concomitant comorbidities may contribute to worse clinical outcomes and increased healthcare resource use. Hospital length of stay (LOS) is an important measure of disease burden and healthcare utilization, yet the determinants of prolonged hospitalization among patients with HZ have not been thoroughly investigated at the national level.

Objectives
To identify comorbidity-related risk factors for prolonged hospitalization among patients admitted with herpes zoster in Italy between 2011 and 2023.

Methods
A retrospective population-based study was conducted using the Italian Hospital Discharge Records database. All hospitalizations associated with HZ between January 1, 2011 and December 31, 2023 were included using ICD-9-CM diagnostic codes. Clinical variables included chronic respiratory diseases, kidney diseases, diabetes mellitus, malignant neoplasms, and autoimmune diseases. Length of stay was analyzed as the main outcome and categorized as short versus prolonged hospitalization according to the overall mean LOS. Poisson regression models adjusted for age and sex were used to estimate the association between comorbidities and prolonged hospitalization, expressed as incidence rate ratios (IRRs) and 95% confidence intervals (95% CIs). The number of hospitalizations with short and long LOS was included as an offset in the models. Data analysis was performed using STATA/BE 18.0.

Results
Between 2011 and 2023, 47,933 hospitalizations with HZ were recorded. Overall, 34.56% of patients experienced a prolonged hospital stay (16,564 hospitalizations). Comorbidities were identified in 27.71% of hospitalizations (13,280 cases). The analysis revealed that HZ patients hospitalized with malignant neoplasms had a 1.46-times higher risk of prolonged length of stay than those without malignant neoplasms (IRR 1.46, 95% CI 1.40–1.53). The risk was also increased among patients with kidney diseases (IRR 1.24, 95% CI 1.17–1.31) and COPD (IRR 1.11, 95% CI 1.09–1.27). Age was the strongest predictor of prolonged hospitalization, with patients aged ≥80 years with malignant neoplasms showing a 2.48-fold higher risk compared with the reference group (95% CI 2.23–2.77).

Conclusions
This nationwide real-world study highlights the substantial impact of selected comorbidities on hospitalization burden among patients with HZ. Malignant neoplasms, kidney diseases, and COPD were independently associated with prolonged hospitalization, while advanced age emerged as the strongest predictor of extended length of stay. These findings underscore the importance of identifying high-risk patients and support targeted preventive strategies, including HZ vaccination, particularly among older adults and clinically vulnerable populations.