Cigarette Smoking and Risk of SARS-CoV-2 infection and Disease Severity Among Adults in an Integrated Health Care System in California.

ABSTRACT

INTRODUCTION: The relationship between cigarette smoking status and SARS-CoV-2 infection and coronavirus disease 2019 (COVID-19) severity is highly debated. We conducted a retrospective cohort study of >2.4 million adults in a large healthcare system to evaluate whether smoking is associated with SARS-CoV-2 infection and disease severity. METHODS: This retrospective cohort study of 2,427,293 adults in KPNC from 3/5/2020 (baseline) to 12/31/2020 (pre-vaccine) included smoking status (current, former, never), socio-demographics, and comorbidities from the electronic health record. SARS-CoV-2 infection (identified by a positive PCR test) and COVID-19 severity (hospitalization, ICU admission or death ≤30 days of COVID-19 diagnosis) were estimated in time-to-event analyses using Cox proportional hazard regression models adjusting for covariates. Secondary analyses examined COVID-19 severity among patients with COVID-19 using logistic regression. RESULTS: During the study, 44,270 patients had SARS-CoV-2 infection. Current smoking was associated with lower adjusted rates of SARS-CoV-2 infection (aHR=0.64 95%CI0.61-0.67), COVID-19-related hospitalization (aHR=0.48 95%CI0.40-0.58), ICU admission (aHR=0.62 95%CI0.42-0.87), and death (aHR=0.52 95%CI0.27-0.89) than never-smoking. Former smoking was associated with a lower adjusted rate of SARS-CoV-2 infection (aHR=0.96 95%CI0.94-0.99) and higher rates of hospitalization (aHR=1.10 95%CI1.03-1.08) and death (aHR=1.32 95%CI1.11-1.56) than never-smoking. Logistic regression analyses among patients with COVID-19 found lower odds of hospitalization for current versus never-smoking and higher odds of hospitalization and death for former versus never-smoking. CONCLUSIONS: In the largest US study to date on smoking and COVID-19, current and former smoking showed lower risk of SARS-CoV-2 infection than never-smoking, while a history of smoking was associated with higher risk of severe COVID-19. IMPLICATIONS In this cohort study of 2.4 million adults, adjusting for socio-demographics and medical comorbidities, current cigarette smoking was associated with a lower risk of both COVID-19 infection and severe COVID-19 illness compared to never-smoking. A history of smoking was associated with a slightly lower risk of COVID-19 infection and a modestly higher risk of severe COVID-19 illness compared to never-smoking. The lower observed COVID-19 risk for current versus never-smoking deserves further investigation. Results support prioritizing individuals with smoking-related comorbidities for vaccine outreach and treatments as they become available.