Blood Group O and Post-Covid-19 Syndrome

Objective The ABO blood group system modulates the inflammatory response and has been involved in COVID-19. O-group protects against SARS-CoV-2 infection, but there are no data regarding post-COVID-19 syndrome (PCS). Our aim was to assess this possible association.Subjects and methods Case-control study in a community setting, with subjects who had experienced mild COVID-19. Cases were PCS+, controls were PCS-, and the exposure variable, O-group. Epidemiological data (age, sex, BMI, smoking, comorbidities), laboratory parameters (inflammatory markers, IgG antibodies, blood type) and clinical data were collected. Composite inflammatory indices were developed. Multivariate analyses were performed.Results We analyzed 121 subjects (56.2% women), mean age 45.7 ± 16 years. Blood group frequencies were 43.3%, 7.7%, 5.7%, and 43.3% for A, B, AB and O, respectively. Thirty-six patients were PCS+. There were no significant differences between cases and controls. Compared to non-O, a higher prevalence of PCS (p=0.036), number of symptoms (p=0.017) and myalgia (p=0.030) were noted in O-group. Concerning inflammatory markers, PCS+ and PCS-showed no differences in A, B, and AB groups. In contrast, O-group PCS+ patients had significantly higher lymphocyte count, higher levels of fibrinogen and CRP, and higher percentages of 3 composite indices, than PCS-subjects. The O-group showed a 4-fold increased risk of PCS compared to non-O (adjusted OR=4.20 [95%CI, 1.2-14]; p=0.023).Conclusion An increased risk of PCS has shown to be associated with O-group, after controlling for confounders. In O-group subjects with PCS, slightly albeit significant, raised levels of fibrinogen, CRP, and lymphocyte count, have been demonstrated.### Competing Interest StatementThe authors have declared no competing interest.### Funding StatementThis study did not receive any funding### Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:The study was approved by the Clinical Research Ethics Committee of Cantabria (Internal Code 2021.102)I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.YesAll data produced in the present study are available upon reasonable request to the authors