Background: COVID-19 (Coronavirus Disease of 2019) is a global pandemic caused by the rapidly spreading SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2). The novel coronavirus has stressed the limits of healthcare systems globally, making early identification of risk factors essential to the functioning of our healthcare systems during this ongoing pandemic. Many risk factors are already known to influence COVID-19 clinical outcomes, however the impact of ABO blood type on severity of disease and mortality amongst patients infected with COVID-19 is still unknown. Recent studies from China, Italy and Spain report an association between COVID-19 risk and blood types while other studies from Turkey and the United States have not or have been inconclusive. The aim of this study is to look for an association between blood type and disease prevalence and severity at a single-center hospital based in Southern California.

Methods: 621 patients hospitalized at Huntington Memorial Hospital in Pasadena with PCR confirmed diagnosis of COVID-19 between March 13th to September 19th 2020 were included in this retrospective study. The different ABO blood types were analyzed for associations with COVID-19 infection and severity of clinical outcomes. Clinical outcomes of severity include need for ICU level of care, ICU length of stay, need for intubation, days on ventilator if intubated, overall hospital length of stay and mortality.

Results: Of the 621 patients who tested positive for COVID-19, 304 had known blood types, of which blood type O was most prevalent at 157 (51.6%, p<0.05, significantly higher than the general population), followed by A at 105 (34.5%), and least by B at 36 (11.8%) and AB at 6 (2%). Differences in mortality rates amongst the blood types were not statistically significant. We noted in our cohort that although blood type O was most prevalent, it was also associated with decreased risk of admission to the ICU by 4.9% and intubation by 14.3% relative to all other blood types combined.

Conclusions: Our results support the growing body of scientific literature that suggests blood type plays a role in COVID-19 susceptibility and disease severity, although not mortality. There is a suggestion from our present study that blood group O individuals may be more susceptible to COVID-19 infection yet experience less severe disease. However, more studies are needed before we can reliably determine whether blood type is a useful marker for identifying at risk individuals for COVID-19.