Smoking and severe illness in hospitalized COVID-19 patients in Japan

• Published in: International journal of epidemiology Vol. 51; no. 4; pp. 1078 - 1087
• Main Authors: Matsushita, Yumi, Yokoyama, Tetsuji, Hayakawa, Kayoko, Matsunaga, Nobuaki, Ohtsu, Hiroshi, Saito, Sho, Terada, Mari, Suzuki, Setsuko, Morioka, Shinichiro, Kutsuna, Satoshi, Mizoue, Tetsuya, Hara, Hisao, Kimura, Akio, Ohmagari, Norio
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 10.08.2022
• Subjects: Original; COVID-19; infectious disease; smoking
• ISSN: 0300-5771; 1464-3685; 1464-3685
• DOI: 10.1093/ije/dyab254

Abstract Background The aim of this study was to identify associations between smoking status and the severity of COVID-19, using a large-scale data registry of hospitalized COVID-19 patients in Japan (COVIREGI-JP), and to explore the reasons for the inconsistent results previously reported on this subject. Methods The analysis included 17 666 COVID-19 inpatients aged 20–89 years (10 250 men and 7416 women). We graded the severity of COVID-19 (grades 0 to 5) according to the most intensive treatment required during hospitalization. The smoking status of severe grades 3/4/5 (invasive mechanical ventilation/extracorporeal membrane oxygenation/death) and separately of grade 5 (death) were compared with that of grade 0 (no oxygen, reference group) using multiple logistic regression. Results were expressed as odds ratios (OR) and 95% confidence intervals (CI) adjusted for age and other factors considering the potential intermediate effects of comorbidities. Results Among men, former smoking significantly increased the risk of grade 3/4/5 and grade 5, using grade 0 as a reference group, with age- and admission-date-adjusted ORs (95% CI) of 1.51 (1.18–1.93) and 1.65 (1.22–2.24), respectively. An additional adjustment for comorbidities weakened the ORs. Similar results were seen for women. Current smoking did not significantly increase the risk of grade 3/4/5 and grade 5 in either sex. Conclusions The severity of COVID-19 was not associated with current or former smoking per se but with the comorbidities caused by smoking. Thus, smoking cessation is likely to be a key factor for preventing smoking-related disease and hence for reducing the risk of severe COVID-19.