Hospital mortality in patients with rare diseases during pandemics: lessons learnt from the COVID-19 and SARS pandemics

Background The threat and experience of pandemics occur differently for different groups. The rare disease population is at particular risk of being further marginalised during pandemics. In this study, our objective was to assess the hospital mortality patterns in the rare disease and the general populations during the coronavirus disease of 2019 (COVID-19) and severe acute respiratory syndrome (SARS) pandemics in Hong Kong. Methods All admission records during the COVID-19 pandemic (January 23-August 23, 2020) and SARS pandemic (March 11-June 30, 2003) were extracted from the local public healthcare database. Patients with rare diseases were identified using one or more of the 1084 10th version International Classification of Diseases and Related Health Problems (ICD-10) codes cross-referenced with 467 ORPHAcodes. Hospital mortality patterns were compared in patients with and without COVID-19/SARS infection. Admission records during the same period in 2019 and 2002 were retrieved for comparison. Results During the COVID-19 pandemic, 407,219 patients were admitted to one or more of the 43 public hospitals in Hong Kong, of which, 13,894 were patients with rare diseases (3.4%). A total of 4381 and 77 patients from the general and rare disease populations were infected with COVID-19. Rare disease patients had an adjusted 3.4 times odds of COVID-19-related hospital mortality compared with that of the general population (95% C.I. 1.24-9.41). COVID-19-related mortality was almost exclusively seen in patients >= 60 years. While age-related increase in mortality was also observed for the general population during the SARS pandemic, the pattern observed in the rare disease population was significantly different, with a 12.5 times higher SARS-related mortality observed in rare disease patients <= 18 years than those in the general population (12.5% vs 1.0%). Patients admitted during the same pandemic periods without coronavirus infection had a significantly higher hospital mortality compared with those admitted one year before the pandemic (p < 0.001). Conclusion This population-based study demonstrated the differential impacts of the COVID-19 and SARS pandemics on the rare disease population. In the era of budget and resource scarcity, this study warrants cautious healthcare planning, with consideration of the rare disease population in healthcare prioritisation.