Tobacco smoking confers risk for severe COVID‐19 unexplainable by pulmonary imaging

BACKGROUND: COVID‐19 is a new pneumonia. It has been hypothesized that tobacco smoking history may increase severity of this disease in the patients once infected by the underlying coronavirus SARS‐CoV‐2 because smoking and COVID‐19 both cause lung damage. However, this hypothesis has not been tested. OBJECTIVE: Current study was designed to focus on smoking history in patients with COVID‐19 and test this hypothesis that tobacco smoking history increases risk for severe COVID‐19 by damaging the lungs. METHODS AND RESULTS: This was a single‐site, retrospective case series study of clinical associations, between epidemiological findings and clinical manifestations, radiographical or laboratory results. In our well‐characterized cohort of 954 patients including 56 with tobacco smoking history, smoking history increased the risk for severe COVID‐19 with an odds ratio (OR) of 5.5 (95% CI: 3.1–9.9; P = 7.3 × 10(−8)). Meta‐analysis of ten cohorts for 2891 patients together obtained an OR of 2.5 (95% CI: 1.9–3.3; P < 0.00001). Semi‐quantitative analysis of lung images for each of five lobes revealed a significant difference in neither lung damage at first examination nor dynamics of the lung damage at different time‐points of examinations between the smoking and nonsmoking groups. No significant differences were found either in laboratory results including D‐dimer and C‐reactive protein levels except different covariances for density of the immune cells lymphocyte (P = 3.8 × 10(−64)) and neutrophil (P = 3.9 × 10(−46)). CONCLUSION: Tobacco smoking history increases the risk for great severity of COVID‐19 but this risk is achieved unlikely by affecting the lungs.