Researchers in Germany and Turkey have conducted a study showing that tobacco smoking is associated with an increased risk of more severe disease in cases of coronavirus disease 2019 (COVID-19).
The systematic meta-analysis revealed that severe COVID-19 occurred 1.5- to 2-times more frequently among smokers and former smokers than among people who had never smoked.
Askin Gülsen (University of Luebeck, Germany) and colleagues say the pandemic should serve as an impetus for at-risk individuals to discontinue smoking.
“It seems very clear that the pandemic period is an opportunity to quit smoking due to the possibility of encountering worse clinical outcomes and complications in patients with smoking history,” they write.
A pre-print version of the paper is available on the server medRxiv*, while the article undergoes peer review.
COVID-19 rapidly swept the globe and quickly became pandemic
Since the first cases of COVID-19 were identified in Wuhan, China, late last year, the causative agent – severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – quickly swept the globe and was declared a pandemic by the World Health Organization on March 11th, 2020.
This highly contagious virus has now infected more than 22 million people worldwide and caused more than 778,000 deaths.
COVID-19 is primarily a respiratory disease, with SARS-CoV-2 targeting the lung epithelium and causing viral pneumonia and acute respiratory distress syndrome, particularly among elderly patients.
The rates of more severe disease and mortality are, therefore, higher in the elderly population and among those with co-morbid diseases such as chronic obstructive pulmonary disease (COPD) and asthma.
The potential role of smoking and COPD
Reports have indicated that COVID-19 progresses more severely among patients with COPD. Since smoking plays a role in the pathogenesis of COPD, Gülsen, and colleagues proposed that it may also affect the progression of symptoms in COVID-19.
However, the researchers say a recent meta-analysis found that smoking did not increase the severity of COVID-19, although that analysis only included five studies. Another meta-analysis that included more studies did find an association between smoking and increased severity of disease.
“The different results of both meta-analyses create confusion about the issue of smoking status,” says the team.
Investigating the association using a systematic meta-analysis approach
Given these inconsistent findings, the researchers set out to determine whether smoking is associated with COVID-19 severity using a systematic meta-analysis approach.
After searching Google Scholar, PubMed, Web of Science, Embase, and Scopus databases for clinical studies that met inclusion criteria, they identified 16 studies published between December 2019 and April 15th, 2020, with data available for 10,797 patients with COVID-19.
The studies all reported smoking status and compared patients with non-severe and severe disease. The non-severe disease was defined as mild, “common-type” disease that did not require ICU care, while severe disease was defined as critical, refractory, requiring ICU care or fatal.
Former and current smoking was more common among patients with severe disease
Of the 10,797 patients included in the analysis, 9,414 (87.2%) had non-severe disease and 1,383 (12.8%) had severe disease.
Among non-severe cases, the prevalence of former smoking was 5.2%, while among severe cases, the prevalence was 12.5%.
Furthermore, the prevalence rates for active smoking were 2.9% among non-severe cases and 5.9% among severe cases.
“Therefore, severe COVID-19 was observed almost 1.5 to 2 times more frequently in history of smoking and current smoking groups,” say Gülsen and team.
When the team analyzed current smoking, specifically, the prevalence of severe disease was 10.7% among non-smokers, compared with 21.2% among active smokers.
The findings support those of previous studies
The researchers say similar findings that current smoking is associated with an increased risk for severe COVID-19 have been reported previously.
“Our analysis adds to this growing consensus in the literature, invoking more studies and examining both a history of smoking and current smoking status in risk for increased COVID-19 severity,” writes the team.
Gülsen and colleagues say one recent meta-analysis indicated that serious complications were observed among 48% of COVID-19 patients who were former smokers and 24% of those who were current smokers. This appears to be due to former smokers being exposed to cigarette smoke for longer and subsequently having developed comorbidities such as COPD, they explain.
Another recent meta-analysis demonstrated that the development of severe COVID-19 was 4.4 times more common among individuals who had COPD.
Smokers at increased risk of severe disease and death
The researchers say there is growing evidence to support the WHO’s warning that smokers are more likely to develop severe COVID-19 and subsequently be at risk of death.
“The SARS-COV-2 epidemic should serve as an impetus for patients and those at risk to maintain good health practices and discontinue smoking,” they write. “In addition, clinicians can pay more attention to the history of smoking of COVID-19 patients, and further research may aim to determine mechanisms that drive or decrease this risk.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.