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TOPIC: Chest Infections TYPE: Original Investigations PURPOSE: COVID-19 (Coronavirus Disease 2019) has caused a devastating pandemic, yet there is still much to learn about the risk factors for the disease. Two through lines surround blood type and male sex. There remains no consensus on whether blood type holds prognostic significance in COVID-19. However, the hypothesis that males are more vulnerable to the virus seems to be gaining traction. This study aims to ascertain if blood type and sex can be used to predict susceptibility, severity, and outcomes of COVID-19. METHODS: All patients who were PCR-tested for SARS-CoV-2 between March 2020-2021 at a 619-bed teaching hospital in Southern California were selected for retrospective chart review. Our primary outcome was mortality, with secondary outcomes of intubation, intensive care unit (ICU) admission and length of stay, and overall length of stay. Continuous data were compared using the Chi-squared test of means. Logistic regression was used to assess for associations between outcomes and patient characteristics. All statistical analyses were performed with Stata. RESULTS: A total of 8,299 patients were included for analysis, of which 1,220 patients had tested positive for SARS-CoV-2. There was no association between blood type and mortality, intubation, or ICU admission among patients with COVID-19. However, blood type was significantly associated with overall length of stay. Patients with blood type O spent on average 1.7 days longer (P = 0.04), and patients with blood type B spent on average 2.6 days longer in the hospital than patients with blood type A (P = 0.02). The association was even stronger for patients with at least one comorbidity, of which patients with blood type B spent on average 3.9 days longer in the hospital than patients with blood type A (P = 0.03). When adjusted for sex, blood type was significantly associated with ICU length of stay. Males with blood type O stayed in the ICU on average 1 day longer than males with blood type A (P = 0.04). CONCLUSIONS: Blood type was not associated with mortality, ICU admission, or intubation, but patients with blood types O and B did have longer hospital stays. In particular, patients with blood type B stayed in the hospital nearly 4 days longer than patients with blood type A if they had at least one comorbidity. CLINICAL IMPLICATIONS: Our study suggests that blood type may not play a leading role in determining disease outcomes of COVID-19. Understanding who is at risk informs the public health strategies that combat this pandemic. These results imply that such efforts may be better placed in areas other than blood type. DISCLOSURES: No relevant relationships by Daryl Banta, source=Web Response No relevant relationships by Michael Guajardo, source=Web Response No relevant relationships by Eva Ma, source=Web Response No relevant relationships by Adrienne Quinn, source=Web Response No relevant relationships by Alberto Russell, source=Web Response No relevant relationships by Ayman Saad, source=Web Response No relevant relationships by Rebecca Wahinehookae, source=Web Response