More Smoking Pack Years Can Mean Worse Outcomes of COVID-19 Infection

It’s not just a patient’s current smoking status that affects their risk of adverse outcomes from COVID-19 infection. It’s lifetime exposure to smoking, according to a study recently published in JAMA Internal Medicine.

“Other studies have focused on whether or not a patient with COVID-19 currently smokes,” says the study’s lead author, Katherine E. Lowe, MSc, a student at Cleveland Clinic Lerner College of Medicine. “But that doesn’t tell you much about the patient’s smoking history. Someone who has smoked a pack a day for one year (one pack year) may have different risk than someone who has smoked a pack a day for 30-plus years. Our study is among the first to look at the cumulative effect of smoking on COVID-19 outcomes.”

Lowe and a team from Cleveland Clinic’s Respiratory Institute reviewed the medical records of more than 7,000 Cleveland Clinic patients with COVID-19 and found a dose-response relationship between smoking pack years and risk of hospitalization and death.

“The more a patient was exposed to smoking, the more likely they were to have worse outcomes from COVID-19,” says Lowe.

Risk increases with number of pack years

Patients in Cleveland Clinic’s COVID-19 registry that tested positive for the virus between March and August 2020 were grouped by smoking history. Of the cohort, 6,020 (84.8%) patients never smoked, 341 (4.8%) smoked 0-10 pack years, 400 (5.6%) smoked 10-30 pack years and 341 (4.8%) smoked more than 30 pack years.

Researchers then evaluated patients’ COVID-19 outcomes and calculated each group’s odds for hospitalization, admission to the ICU and death due to COVID-19. They found that, when adjusted for age, race and gender, patients who smoked more than 30 pack years were 2.25 times more likely than never smokers to be hospitalized due to COVID-19. They also were 1.69 times more likely to be admitted to the ICU and 1.89 times more likely to die due to COVID-19.

“These results really weren’t surprising,” says Lowe. “Smoking history is linked with adverse respiratory outcomes in other diseases. And current and former smokers are more likely to have not only lung damage but hypertension, coronary artery disease and heart failure — comorbidities already associated with adverse outcomes in COVID-19.”

Former smokers have same risk as current smokers

Of those with a smoking history, 172 (15.9%) currently smoked and 910 (84.1%) had quit smoking. However, current smoking status did not change the odds. Both current and former smokers in each group had similar outcomes.

“We had a low proportion of current and former smokers in our cohort,” says Lowe. “But that could be because smoking history isn’t consistently collected in the medical record. ‘Are you a smoker?’ is not the same question as ‘Were you ever a smoker?’”

Former smokers may not be recognized in the medical record, and thus may have been incorrectly grouped with nonsmokers, she notes. That may have skewed the baseline results of nonsmokers. As such, the increased risk of adverse COVID-19 outcomes in smokers may actually be greater than reported.

Clinical implications

This study is notable because there is a significant population of older U.S. adults who smoked when they were younger, says senior author Amy Attaway, MD, a Cleveland Clinic pulmonologist.

“Patients who smoked for years — even though they quit years ago — may still be highly susceptible to complications from COVID-19,” says Dr. Attaway. “We need to encourage them to be extra vigilant about wearing a mask, distancing and getting the COVID vaccine as soon as they’re able.”