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Review
. 2020 Jun 25:11:2040622320935765.
doi: 10.1177/2040622320935765. eCollection 2020.

Current smoking, former smoking, and adverse outcome among hospitalized COVID-19 patients: a systematic review and meta-analysis

Konstantinos Farsalinos  1 , Anastasia Barbouni  2 , Konstantinos Poulas  3 , Riccardo Polosa  4 , Pasquale Caponnetto  4 , Raymond Niaura  5
Affiliations
Review

Current smoking, former smoking, and adverse outcome among hospitalized COVID-19 patients: a systematic review and meta-analysis

Konstantinos Farsalinos et al. Ther Adv Chronic Dis. .

Abstract

Background: The purpose of this study was to examine the prevalence and effects of current smoking on adverse outcomes among hospitalized COVID-19 patients.

Methods: A systematic review of the literature (PubMed) identified 18 (from a total of 1398) relevant studies. Pooled current smoking prevalence was compared with the gender-adjusted and gender and age-adjusted, population-based expected prevalence by calculating prevalence odds ratio (POR). The association between current, compared with non-current and former, smoking and adverse outcome was examined. A secondary analysis was performed by including 12 pre-publications (30 studies in total). All analyses were performed using random-effects meta-analysis.

Results: Among 6515 patients, the pooled prevalence of current smoking was 6.8% [95% confidence interval (CI): 4.8-9.1%]. The gender-adjusted POR was 0.20 (95% CI: 0.16-0.25, p < 0.001), and the gender and age-adjusted POR was 0.24 (95% CI: 0.19-0.30, p < 0.001). Current smokers were more likely to have an adverse outcome compared with non-current smokers [odds ratio (OR): 1.53, 95%CI: 1.06-2.20, p = 0.022] but less likely compared with former smokers (OR: 0.42, 95% CI: 0.27-0.74, p = 0.003). When pre-publications were added (n = 10,631), the gender-adjusted POR was 0.27 (95% CI: 0.19-0.38, p < 0.001) and the gender and age-adjusted POR was 0.34 (95% CI: 0.24-0.48, p < 0.001).

Conclusion: This meta-analysis of retrospective observational case series found an unexpectedly low prevalence of current smoking among hospitalized patients with COVID-19. Hospitalized current smokers had higher odds compared with non-current smokers but lower odds compared with former smokers for an adverse outcome. Smoking cannot be considered a protective measure for COVID-19. However, the hypothesis that nicotine may have a protective effect in COVID-19 that is partially masked by smoking-related toxicity and by the abrupt cessation of nicotine intake when smokers are hospitalized should be explored in laboratory studies and clinical trials using pharmaceutical nicotine products.

Keywords: COVID-19; SARS-CoV-2; adverse outcome; hospitalization; inflammation; nicotine; smoking.

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Conflict of interest statement

Conflict of interest statement: The authors declare that there is no conflict of interest.

Figures

Figure 1.
Figure 1.
POR of current smoking among hospitalized patients with COVID-19 (gender-adjusted). Data from 18 published studies. POR, prevalence odds ratio.
Figure 2.
Figure 2.
POR of current smoking among hospitalized patients with COVID-19 (gender and age-adjusted). Data from 18 published studies. POR, prevalence odds ratio.
Figure 3.
Figure 3.
Association between current (versus non-current) smoking and adverse outcome in COVID-19. Data from 18 published studies.
Figure 4.
Figure 4.
Association between current (versus former) smoking and adverse outcome in COVID-19. Data from 4 published studies.
See this image and copyright information in PMC

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