(C-045) Acute All-cause hospitalization following medically-attended acute gastroenteritis (AGE) and norovirus AGE among patients with underlying chronic conditions in the United States, 2022–2024

Background: Norovirus (NoV) is the leading cause of acute gastroenteritis (AGE) in the United States (US), causing an estimated 21 million cases annually. Some studies have shown that underlying chronic conditions, such as chronic kidney disease (CKD) or immunocompromising conditions, can influence the severity of AGE outcomes and sequelae. The objective of this study was to characterize the occurrence of acute all-cause hospitalization within 3 days following medically-attended AGE and NoV AGE by patient age and underlying chronic conditions to inform disease burden and prevention strategies for high-risk populations.

Methods: We conducted a retrospective cohort study using Optum’s de-identified Clinformatics® Data Mart Database (Optum® CDM) of commercially insured and Medicare Advantage members. AGE and NoV AGE episodes ≥14 days apart were identified via ICD-10 codes from medical encounters between July 1, 2022–June 30, 2024. Demographics and underlying medical conditions (e.g., cardiovascular disease (CVD), CKD, cancer, immunocompromising conditions) were identified in data from the year prior to index. Acute hospitalization was assessed within 3 days of index date. We estimated incidence of AGE medical encounters using ICD-10 codes, and analyzed the proportion with acute hospitalizations by age group and by underlying medical conditions.

Results: AGE encounter incidence increased with age, with highest incidence in oldest adults ≥80 years (105 cases/1000 person-years [PY]) and among the youngest children <5 years (86 cases/1000 PY). Among 1.79 million AGE encounters, 11% were hospitalized, with higher rates in those with underlying medical conditions (13%) vs. without (2%) (p < 0.01). Of 6,252 encounters with cause-specified NoV, known to be underutilized in routine care, 42% were hospitalized—49% with underlying medical conditions and 14% without (p < 0.01). The most prevalent underlying medical conditions among AGE and NoV AGE cases were CVD (63%, 72%), chronic respiratory disease (28%, 38%), diabetes (27%, 31%), and CKD (19%, 30%).

Conclusions: Increased all-cause hospitalizations were seen within 3 days of AGE and NoV AGE encounters for all patients with underlying chronic conditions, which may indicate greater disease severity, propensity to admit patients with underlying conditions due to heightened concern or exacerbation of underlying conditions, or limited access to timely outpatient care and management of AGE symptoms. Although NoV is a leading cause of AGE, it is not routinely tested and, therefore, severely underestimated in claims data. These findings demonstrate the significant burden of AGE on the healthcare system, particularly among older adults and some high-risk groups.