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Data sources The national electronic health records of the Hamad Medical Corporation (HMC) in the State of Qatar.Data extraction and synthesis This case-control study included 568 patients from the HMC electronic database for data eliciting from 27 February 2020 to 31 July 2020. Patients with coronavirus disease 2019 (COVID-19) complications were considered as cases. Controls were defined as COVID-19 patients without major complications (discharged). Multivariate logistic regression was performed to assess the association between the exposures (periodontitis, demographics and medical conditions) and outcomes (COVID-19 complications). The association was adjusted for possible confounding factors. Additionally, sensitivity analyses were performed to account for stronger risk factors of the determined complications. The results were reported using the odds ratio (OR) and 95% confidence intervals (CIs). Laboratory data (blood parameters concerning the course of COVID-19) were also compared between the case and control groups.Results The patients were divided into 40 cases and 528 controls. Among the patients with periodontitis, 12.8% (33/258) went through COVID-19 complications, whereas 2.2% (7/310) of those without periodontitis experienced complications. The adjusted OR of patients with periodontitis was 3.67 (95% CI 1.46-9.27) for all COVID-19 complications, 8.81 (95% CI 1.00-77.7) for death, 3.54 (95% CI 1.39-9.05) for intensive care unit admission and 4.57 (95% CI 1.19-17.4) for the need of assisted ventilation. After conducting subgroup analyses for age, diabetes and smoking, periodontitis was still significantly associated with all the outcomes. Laboratory biomarkers (haemoglobin A1c, white blood cells and C-reactive protein) had higher levels in COVID-19 patients with periodontitis than those without periodontal disease.Conclusions This study concluded that periodontitis was significantly associated with higher risks of COVID-19 complications and higher blood marker levels. These results, however, are not of high quality and further research in this regard is required.