Intensity of Past Smoking Linked to COVID-19 Severity

Cumulative exposure to cigarette smoke was associated with more severe outcomes among individuals testing positive for COVID-19, including higher risks of hospitalization and death, researchers found.

Compared with never smokers, those with smoking histories of more than 30 pack-years had 2.25 higher odds of hospitalization due to COVID-19 (95% CI 1.76-2.88), after adjustment for age, race, and sex, reported Katherine Lowe, MSc, of Cleveland Clinic Lerner College of Medicine of Case Western Reserve University School of Medicine, and colleagues in a JAMA Internal Medicine research letter.

Mortality risk was also substantially higher in heavy smokers (OR 1.89 95% CI 1.29-2.76) after those adjustments. But when further adjusted for comorbidities and use of certain medications, the association with mortality diminished into nonsignificance.

Additionally, odds ratios were intermediate for smokers with less cumulative exposure, pointing to a dose-response relationship.

Previous smoking appeared to be the key risk factor, as odds ratios for severe outcomes were similar for current smokers and those who had quit, Lowe and colleagues said.

The CDC currently lists smokers as one of the groups at high risk for severe COVID-19; yet research on the role of smoking in COVID-19 outcomes has been "limited and contradictory," Lowe's group wrote, with no studies having assessed cumulative smoking exposure in pack-years.

The group drew on data from the COVID-19 Registry for roughly 7,000 patients in Ohio and Florida, of whom about 6,000 had never smoked. Adults testing positive for COVID-19 from March 8 to August 25 and had full smoking information available were included.

Smokers with more than 30 pack-years were older (mean age 71 vs 49 for never smokers) and significantly more likely to be white (72% vs 56%, respectively) and have obesity (37% vs 27%). Heavy smokers were also significantly more likely to have comorbidities, including 86% with hypertension versus 37% of never smokers.

Limitations to the study include use of data exclusively from tertiary care medical centers, which limits its generalizability to the population at large. They also noted former smokers might have been recorded as never smokers, and pack-years potentially underestimated.

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