A decade of endemic human coronaviruses: epidemiological patterns and clinical significance in an adult cohort at a tertiary care hospital in Germany.

INTRODUCTION: The four endemic human coronaviruses (HCoV-OC43, -NL63, -HKU1, and - 229E) are common respiratory pathogens. Studies on HCoV epidemiology in Germany are limited. Therefore, this study aimed to characterize the epidemiology and clinical significance of HCoV-infections in adult patients over 11 seasons at a tertiary care hospital in Germany. METHODS: Over 29,000 respiratory specimens were analyzed using nucleic acid amplification assays for respiratory pathogens between 2012 and 2022. Additionally, clinical data were retrospectively retrieved from patient records for cases with confirmed HCoV infections. RESULTS: During the study period, 469 unique adult cases were identified. HCoV-OC43 (38.6%) and HCoV-NL63 (25.6%) were most frequently detected, followed by HCoV-229E (22.4%) and HCoV-HKU1 (13.4%). HCoVs exhibited strong seasonality, with most detections occurring during the winter months, peaking between January and March. Sporadic detections of HCoV-OC43 and HCoV-NL63 were observed in summer. While HCoV-NL63 was detected year-round, HCoV-OC43 and HCoV-HKU1 displayed a biennial circulation pattern. No consistent pattern was observed for HCoV-229E. Across all HCoV cases HCoV-OC43 were more frequently associated with dyspnea (48.1%, p = 0.004), lower respiratory tract infection (45.3%; p = 0.018), exacerbation of obstructive lung disease (17.6%, p = 0.002), and systemic prednisolone administration (16%, p = 0.007). HCoV-HKU1 infection was more frequently detected in patients with lymphoma (35.6%, p = 0.002) and associated with higher in-hospital mortality (18.6%, p = 0.042). Overall, 119 co-infections (26.0%) were identified, including viral (10.9%) bacterial (10.5%), and fungal (1.7%) pathogens. Co-infections were significantly associated with LRTI (p < 0.001), need for mechanical ventilation (p = 0.001), and ICU admission (p < 0.001). CONCLUSION: Endemic coronaviruses exhibit complex circulation patterns characterized by distinct seasonality. The cyclic behavior of HCoV-OC43 and HCoV-HKU1 suggests possible immunological interactions within this virus family. The clinical presentation and severity of HCoV infections are highly dependent on the age group, comorbidities of the affected patients, and co-infections.