The association between smoking and COVID-۱۹ severity: possiblemechanisms

Background: Smoking adversely affect the lung immune function by increasing the risks ofseverity of various infectious diseases such as COVID-۱۹. The association between smoking onCOVID-۱۹ outcomes including the need for ventilation, and hospitalization in intensive care units(ICU) as well as death have been sporadically studied and conflicting results have been reported.Given the gap in the literature, we conducted a review study of published reviews in this regard.Methods: The published studies were searched through MEDLINE, Embase, CENTRAL, Web ofScience, Lit COVID, and Europe PMC, between December ۱st, ۲۰۱۹ and February ۲۰th, ۲۰۲۱.Studies included ۶۶۹۷۷ individuals with positive COVID-۱۹ infection. The status of patients weredivided into smokers, non-smokers, ex-smokers and unspecified-smokers.Results: Mortality is the most common outcome evaluated to study the association betweensmoking and COVID-۱۹. Most studies approved that smoking increased the mortality,hospitalization, ICU admission, mechanical ventilation and symptom severity. Patients with asmoking history had significantly increased risk of severe COVID-۱۹, in-hospital mortality,necessity of mechanical ventilation. Based on analysis performed on ۵۳۲ patients in one group ofstudies, there was no significant difference in rate of mortality between smokers and ex-smokers.The exacerbation of COVID-۱۹ symptoms and mortality in smokers might be resulted from poormucociliary clearance, release of pro-inflammatory cytokine including interleukin-۶, interleukin-۸,and tumor necrosis factor alpha, increased expression of angiotensin converting enzyme ۲ in therespiratory tract as well as damaged endothelial and abnormal barrier function against virus. Onestudy reported high risk of pulmonary embolism in COVID-۱۹ patients with smoking history.Although most of the studies demonstrated strong relation between smoking and COVID-۱۹severity, there were some reports with lack of significant attribution. Only one report exhibiteddecreased COVID-۱۹ severity in smokers.Conclusion: Although further evaluations are warranted, the outcome of current review confirmedan association between any smoking history and mortality upon COVID-۱۹ infection. Preventionand cessation of smoking should be considered as the main priority for all societies within theCOVID-۱۹ pandemic and even after that

کلیدواژه ها:

COVID-۱۹ ، Smoking ، Mortality ، Hospitalization ، ICU admission ، Mechanism.