Oral hygiene risk factor

Sir, I would like to inform readers about the potential connection between high bacterial load in the mouth and complications associated with COVID-19 infection.

Oral hygiene should be improved during a COVID-19 infection in order to reduce the bacterial load in the mouth and the risk of a bacterial superinfection. We recommend that poor oral hygiene be considered a risk to COVID-19 complications, particularly in patients predisposed to altered biofilms due to diabetes, hypertension or cardiovascular disease. Bacteria present in patients with severe COVID-19 are associated with the oral cavity, and improved oral hygiene may reduce the risk of complications. Whilst COVID-19 has a viral origin, it is suspected that in severe forms of the infection, bacteria plays a part, increasing the chance of complications such as pneumonia, acute respiratory distress syndrome, sepsis, septic shock and death.1

The development and severity of complications following a COVID-19 infection depend on numerous host and viral factors that will affect a patient's immune response. Whilst 80% of patients with COVID-19 infections have mild symptoms, 20% progress to have a severe form of infection associated with higher levels of inflammatory markers (Interleukin 2, 6, 10) and bacteria.2,3 They also exhibit a remarkably higher neutrophil count and lower lymphocyte count than in mild patients.4 A high neutrophil count is abnormal for a viral infection, but common for a bacterial infection, suggesting that in severe cases of COVID-19, bacterial superinfection is common.

The three main comorbidities associated with an increased risk of complications from COVID-19 are diabetes, hypertension and cardiovascular disease.5 These comorbidities are also associated with altered oral biofilms and periodontal disease. Periodontopathic bacteria are implicated in systemic inflammation, bacteraemia, and pneumonia.6 Bacteria present in the metagenome of patients severely infected with COVID-19 included high reads for Prevotella, Staphylococcus, and Fusobacterium, all usually commensal organisms of the mouth.7 Over 80% of patients in ICU exhibited an exceptionally high bacterial load,3 and treatment has been successful with a dual regime of an antiviral and an antibiotic.8 It is clear that bacterial superinfections are common in patients suffering from a severe case of COVID-19.


  1. 1.

    World Health Organization. Clinical management of severe acute respiratory infection when COVID-19 is suspected. Interim guidance, 13 March 2020. Available at: (accessed April 2020).

  2. 2.

    Gong J. Correlation Analysis Between Disease Severity and Inflammation-related Parameters in Patients with COVID-19 Pneumonia. Tongji Hospital, 2020.

  3. 3.

    Liu J. Neutrophil-to-Lymphocyte Ratio Predicts Severe Illness Patients with 2019 Novel Coronavirus. Beijing Ditan Hospital, 2020.

  4. 4.

    Zheng M, Gao Y, Wang G et al. Functional exhaustion of antiviral lymphocytes in COVID-19 patients. Cell Moll Immunol 2020; DOI: 10.1038/s41423-020-0402-2.

  5. 5.

    Zhou F, Yu T, Du R et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: A retrospective cohort study. Lancet 2020; 395: 1054-1062.

  6. 6.

    Nagaoka K. Prevotella intermedia induces severe bacteremic pneumococcal pneumonia in mice with upregulated platelet-activating factor receptor expression. American Society for Microbiology, 2014.

  7. 7.

    Chakraborty S. Metagenome of SARS-Cov2 patients in Shenzhen with travel to Wuhan: OSF Preprints, 2020.

  8. 8.

    Gautret P, Lagier J-C, Parola P et al. Hydroxychloroquine and azithromycin as a treatment of COVID-19: Results of an Open-Label Non-randomized trial. Int J Antimicrob Agents 2020; DOI: 10.1016/j.ijantimicag.2020.105949.

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Correspondence to V. Sampson.

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Sampson, V. Oral hygiene risk factor. Br Dent J 228, 569 (2020).

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