A retrospective cohort study of outcomes in hospitalised COVID-19 patients during the first pandemic wave in Ireland.

Aim: Describe the epidemiology, resource use and adverse outcomes of COVID-19 patients hospitalised during wave 1 of the COVID-19 pandemic in Ireland. Use this data to identify specific cohorts at high risk of adverse outcomes and to inform acute hospital requirements for future COVID-19 waves in Ireland.

Methods: The Health Service Executive's (HSE) Hospital Inpatient Enquiry (HIPE) system produced a daily database of COVID-19 discharge episodes from the onset of the COVID-19 pandemic in Ireland. This study analysed data on episodes of COVID-19 hospitalisation recorded between February 29 and July 31, 2020. A deterministic record linkage process transformed records from episode to patient level. Logistic regression modelling identified factors associated with long length of stay (LLOS), intensive care unit (ICU) admission and inhospital mortality.

Results: Median length of stay was 9 days; 12.8% of patients had ICU admission and 16.6% died in hospital. Male patients were more likely to have ICU admission and die in hospital. Likelihood of LLOS and inhospital mortality increased with age. Obesity, hypertension and diabetes were associated with ICU admission while chronic kidney disease and chronic obstructive pulmonary disease were associated with inhospital mortality. Nursing home residents were less likely to be admitted to ICU and more likely to die in hospital compared to patients admitted from home.

Conclusion: This study provides patient-level epidemiological characterisation of hospitalisations during the first COVID-19 pandemic wave in Ireland. The higher risk of adverse outcomes in older age groups supports the age-based prioritisation of COVID-19 vaccinations currently used in Ireland.