key: cord-0835942-u0g8sc79
authors: Boudin, Laurys; Dutasta, Fabien
title: Relationship between ABO blood groups and COVID-19: study design matters
date: 2020-09-28
journal: Clin Infect Dis
DOI: 10.1093/cid/ciaa1473
sha: e176f3b450520fe70989270537f1871b8c88c770
doc_id: 835942
cord_uid: u0g8sc79

nan

M a n u s c r i p t 2 Dear Editor:,

We read with interest the study by Zhao and colleagues [1] describing a relationship between the ABO blood groups and the COVID-19 susceptibility. In this case control study, authors compared ABO blood group distributions in 2,173 COVID-19 patients with local control populations and found that blood group A was associated with an increased risk of infection (susceptibility) or death (severity), whereas group O was associated with a decreased risk of infection or death.

Concerning susceptibility, numerous studies [1-9] (Table 1) have analysed the relationship between blood group and COVID-19. Almost all other studies also compared ABO distributions on patients hospitalized with SARS-CoV-2 infection with ABO types from a background healthy population in the same area and found similar results. Three studies have a different design. The first one epidemiologically analysed the relationship between blood-group distribution (i.e. proportion of subjects with blood-group O, and A, B, and AB ) and SARS-CoV-2 infection (i.e. COVID-19 prevalence) in nations around the world [8] . The second one compared the distribution of SARS-CoV-2 in blood groups in people exposed at the same time and in the same place (an aircraft carrier) to SARS-CoV-2 [9] . None of these two studies found a relationship between ABO blood group and COVID-19 susceptibility. The third one included all patients who received COVID-19 testing across five hospitals and found that patients with blood types B and AB who received a test were more likely to test positive [7] . Thus, results differ according to the study design. Case control studies could be criticized for the lack of data about patient exposure to the virus before developing COVID-19 and probably not including all forms of the disease. As specified by the authors chronic preexisting medical conditions that could potentially affect the chance and severity of SARS-CoV-2 infection were not addressed in the study. One important epidemiological clinical characteristic of COVID-19 is the enrichment of hospitalized patients with cardiovascular disease carriers. Since non-O and especially the A allele of the ABO blood group is associated with an increased risk of developing cardiovascular diseases as reported by several studies [10] this might influence the observed ABO distribution when comparing hospitalized versus non hospitalized cohorts. However, concerning severity literature shows contradictory results (Table 1 ) and a metaanalysis showed no relationship between ABO blood group and COVID-19 mortality.

In conclusion, considering all the publications on the subject, we believe that in this SARS-CoV-2 epidemic period, no one can consider themselves more or less at risk in relation to their blood type.

We declare no conflict of interest concerning this topic. Funding: No funding

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A c c e p t e d M a n u s c r i p t 3 A c c e p t e d M a n u s c r i p t 4