Current smoking is not associated with COVID-19

We have read with interest the paper by Leung et al. [1] recently published in the European Respiratory Journal, reporting a higher expression of the protein angiotensin-converting enzyme II (ACE-2) in the small airway epithelia of smokers and COPD patients with putatively important implications for coronavirus disease 2019 (COVID-19) patients, since ACE-2 has been shown to be the receptor utilised by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to enter the host cell [2]. Furthermore, the authors reported that current smokers showed a higher expression of ACE-2 gene expression than non-smokers, concluding that the increased ACE-2 expression in smokers might predispose to increased risk of SARS-CoV-2 infection [1].

Short abstract

Despite the main complications of SARS-CoV-2 infection regard lung involvement, the prevalence of current smoking in COVID-19 patients is very low, thus questioning the role of coexisting active smoking as a risk factor for COVID-19 pneumonia https://bit.ly/3eUnl1R

To the Editor:

We have read with interest the paper by Leung et al. [1] recently published in the European Respiratory Journal, reporting a higher expression of the protein angiotensin-converting enzyme II (ACE-2) in the small airway epithelia of smokers and COPD patients with putatively important implications for coronavirus disease 2019 (COVID-19) patients, since ACE-2 has been shown to be the receptor utilised by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to enter the host cell [2]. Furthermore, the authors reported that current smokers showed a higher expression of ACE-2 gene expression than non-smokers, concluding that the increased ACE-2 expression in smokers might predispose to increased risk of SARS-CoV-2 infection [1].

To this regard, all epidemiological data published so far reported that COVID-19 patients show a very low prevalence of smokers, with no significant association between current smoking and severe disease in COVID-19 patients [3–6].

At the University-Hospital of Padova, located in the Veneto Region, one of the areas in Italy most affected by COVID-19, between 15 March and 10 April, 2020, 132 patients were assessed in our clinic for SARS-CoV-2 related pneumonia. The analysis of patients' smoking history showed that no-one was a current smoker, with 112 patients (84.8%) who had never smoked and 20 (15.2%) who were former smokers. These data are in agreement with those from China [3–6]. Furthermore, there was no difference in the disease severity between patients who never smoked and former smokers. These data are even more striking if we consider that the percentage of current smokers in Italy and in the Veneto Region is 25.7% and 22.7%, respectively (www.epicentro.iss.it/passi/dati/fumo).

Thus, the conclusions of Leung et al. [1] to consider cigarette smoking as a severe risk factor for COVID-19 pneumonia are in contrast with the strong and consolidated epidemiological data coming from China [3–6] that have been confirmed also in our patients.

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