Researchers in the United States conducted a detailed analysis that looked at whether smoking increased or decreased the risk of testing positive for Coronavirus Disease 2019 (COVID-19).
The team’s retrospective chart review of patients who tested positive or negative for COVID-19 while in hospital found that smoking was associated with an increased risk of testing positive in patients aged 40 to 49 years.
On the other hand, men and patients aged 50 to 69 years had an increased risk of testing positive for COVID-19 regardless of their smoking status.
The study also found that no history of smoking was associated with a reduced risk of positive testing in patients with heart failure (CHF), chronic obstructive pulmonary disease (COPD), and Parkinson’s disease.
“This is the first study to show that smoking increases the risk of COVID-19 positivity in 40-49 year old patients, while not smoking reduces the risk of COVID-19 positivity in patients with heart failure, COPD and Parkinson’s”, Write the researchers at the Sacred Heart Medical Center for Peace Health in Oregon and the University of Illinois in Chicago.
A pre-print version of the paper is available on the medRxiv * server while the article is being peer-reviewed.
Figure 1 below shows that while COVID-19 positive patients had a significantly lower prevalence of current smokers (9%), they also had a higher prevalence of never smokers (54%) compared to COVID-19 negative patients. Both COVID-19 positive (37%) and negative (39.33%) patients had almost the same prevalence among ex-smokers.
The results so far have been inconsistent
Since the COVID-19 outbreak began late last year (2019) in Wuhan, China, the link between smoking and the risk of developing the disease has been of great interest to researchers.
Studies have reported a high prevalence of never-smokers and a low prevalence of current and former smokers among COVID-19 patients, leading some to speculate that smoking reduces the risk of testing positive for COVID-19
“However, these studies never compared positive and negative COVID-19 patients,” said Samson Barasa and colleagues. In addition, current and former smokers positive for COVID-19 have been reported to have an increased risk of morbidity, mortality and the need for mechanical ventilation assistance.
In addition, a population-based study conducted in Israel found that smokers were never at a higher risk of testing positive for COVID-19 compared to current and former smokers, while an analysis of data from the UK Biobank found no association between smoking and COVID- . 19 positivity.
Figure 2 below shows that 40-49-year-old patients had the highest (60.98%) and lowest (14.63%) prevalence of never and former smokers, respectively. In contrast, the 70-100-year-old patients had the lowest (4.79%) and the highest (52.05%) prevalence of current and former smokers, respectively. The prevalence of current smokers was almost the same among 20 to 39 year olds (22%), 40 to 49 year olds (24%) and 50 to 69 year olds (23%).
What did the researchers do?
Samson Barasa and his team performed a retrospective chart review of hospital patients (ages 18+) who tested positive (n = 117) or negative (n = 277) for COVID-19 between February 2, 2020 and October 21, 2020 .
Using Poisson regression analysis, the data were stratified for smoking status (never smoking versus a history of current or previous smoking) and, after adjustment, analyzed for a range of potential confounders.
The study found that while COVID-19 positive patients had a significantly lower prevalence of current smokers than COVID-19 negative patients (9% versus 18%), they also had a higher prevalence of never-smokers (54% versus 42%) .
The prevalence of ex-smokers was similar in the positive and negative patients at 37% and 39%, respectively.
How did the risk of testing positive differ between the groups?
Current and former smokers ages 40 to 49 were more likely to test positive for COVID-19 than non-smokers in the same age group.
In contrast, male patients and patients aged 50 to 69 years were more likely to be positive for COVID-19 regardless of their smoking status.
“Although men and those 50-69 year old patients were at a higher risk of testing positive for COVID-19, smoking status had no impact on their risk of COVID-19 positivity,” the team writes.
Patients with end-stage kidney disease and non-COVID-19 viral respiratory diseases had a lower risk of testing positive for COVID-19 regardless of their smoking status.
However, patients with CHF, COPD, and Parkinson’s disease were less likely to test positive for COVID-19 from non-smokers.
What are the implications for the study?
“Based on our study results, smoking increases the risk of testing positive for COVID-19 in current and former smokers aged 40 to 49, while smoking never decreases the risk of testing positive for COVID-19 in CHF, COPD, and Parkinson’s patients, ”say Barasa and colleagues.
On the other hand, men and people aged 50 to 69 years old are more likely to test positive for COVID-19 regardless of their smoking status.
“Our study emphasizes that smoking does not reduce the risk of testing positive for COVID-19, while smoking never increases the risk of COVID-19 positivity, even though COVID-19 positive patients have a low prevalence for smokers a high prevalence by non-smokers, ”concludes the team.