Obesity Biggest Risk for COVID-19 Pneumonia, After Age, Male Sex

Marlene Busko

November 05, 2020

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In a large international study of patients admitted to the intensive care unit (ICU) with COVID-19, the likelihood of having severe pneumonia (ie, needing invasive mechanical ventilation) increased stepwise with increasing body mass index (BMI) — independent of diabetes, hypertension, dyslipidemia, or current smoking.

The main finding was a linear correlation between BMI and need for invasive mechanical ventilation, after adjustment for center, age, sex, and other prespecified metabolic risk factors.

Risk was "highest for older people and males, but the next most important risk factor to developing severe pneumonia if infected [was] obesity," said François Pattou, MD, Centre Hospitalier Universitaire de Lille, France, who presented the findings at the ObesityWeek® Interactive meeting. The results were also recently published in a preprint article in The Lancet.

Pattou and colleagues first reported back in April that obesity is one of the biggest risk factors for severe COVID-19 infection, especially in younger patients. Many further reports linked the two, and the French researchers then set out to conduct the current large international multicenter cohort study.

"The high number of patients included here [allowed us] to disentangle the role of various metabolic cofactors and to show that obesity, not diabetes or hypertension, was the main determinant of severe pneumonia [after age and gender]," Pattou told Medscape Medical News.

And the impact of obesity was most pronounced in women younger than 50.

Patients With Severe Obesity Must Protect Themselves

Of interest, the study also found an "obesity paradox" for mortality after admission to the ICU.

Specifically, compared with lean patients (BMI < 25 kg/m2), those with severe obesity (obesity class III, BMI ≥ 40 kg/m2) had an increased risk of dying within 28 days of admission to ICU. But patients with overweight to moderate obesity (BMI 25-39.9 kg/m2) had a lower risk of this outcome.

"The second original finding of our study," Pattou continued, was the “nonlinear relation observed between BMI and all-cause mortality rate in ICU patients."

Matteo Rottoli, MD, PhD, author of a related study reported by Medscape Medical News in July, said the new trial "confirms the findings of our study, which are that obesity is an independent risk factor for intensive care admission and death."

Rottoli, from Alma Mater Studiorum, University of Bologna, Italy, and colleagues found that in their population of patients with COVID-19, a BMI > 35 kg/m2 was associated with a greater risk of death.

The takeaway message from the research is that "obesity should be considered one of the most important parameters to identify the population at risk" of getting COVID-19 who need to take extra precautions such as social distancing, Rottoli stressed.

Pattou agrees, particularly when it comes to severe obesity.

Intensive care physicians have learned a lot in the past months about COVID-19 pneumonia and how to address it (such as not precipitating intubation, using corticosteroids), he explained. 

"Importantly, the general population has also learned a lot, and we can hope that patients with obesity, especially those with severe obesity, will take extra measures to protect themselves, resulting in a decrease of the incidence of severe pneumonia in young and severely obese patients," he added.

Untangling BMI From Other Metabolic Risk Factors

Pattou said that from December 16, 2019 to November 1, 2020, more than 45 million people worldwide tested positive for COVID-19 and more than 1.2 million people died from it.

Multiple studies have reported that among people with COVID-19 those with obesity are at higher risk of hospitalization, ICU admission, invasive ventilation, and death, but it had not been clear if BMI was an independent risk factor.

Pattou and colleagues aimed to examine the relationship between BMI and COVID-19 pneumonia severity — defined by the need for mechanical ventilation (primary outcome) — as well as 28-day all-cause mortality (secondary outcome) among patients admitted to the ICU.

They also sought to disentangle the effect of BMI from other metabolic risk factors (diabetes, hypertension, dyslipidemia, and current smoking) and examine the influence of age and sex on outcomes.

They performed a retrospective analysis of 1461 patients with confirmed COVID-19 (positive reverse PCR test using a nasal or pharyngeal swab specimen) who were admitted to the ICU at 21 centers from February 19 to May 11, 2020.

Participating centers were in France (13), Italy (three), the United States (one in Bronx, New York, and one in Providence, Rhode Island), Israel (one), Belgium (one), and Spain (one).  

Close to three quarters of patients were men (73%), which is similar to multiple other studies, Pattou said. Patients were a mean age of 64 years and had a mean BMI of 28.1 kg/m2.

Half of patients had hypertension (52%), 29% had diabetes, 29% had hyperlipidemia, and 6.5% were current smokers.

Close to three quarters (74%) required invasive mechanical ventilation and 36% died within 28 days of ICU admission.

Each 5-kg/m2 increase in BMI was associated with a 27% increased risk of mechanical ventilation in the overall cohort and a 65% increased risk of this outcome among women younger than 50 years, after adjusting for other risk factors.

Male sex and each 10-year increase in age were associated with an 82% and a 17% increased risk of ventilation, respectively, but hypertension, diabetes, hyperlipidemia, and current smoking were not associated with a greater risk.

After adjusting for center, age, sex, and prespecified metabolic risk factors, obesity class III (BMI ≥ 40 kg/m2) was associated with a 68% increase in mortality compared with lean patients.

The findings were similar across different centers.

"To our knowledge, this study represents the first international collaborative effort to explore the association of BMI with the outcomes of pneumonia among COVID-19 patients admitted to ICU," say the investigators.

They conclude that "available evidence should foster more focused and effective interventions in COVID-19 patients with the highest risk of severe pneumonia, in order to reduce future strain on intensive care resources worldwide, and inform physio-pathological research to elucidate the mechanism of severe lung damage in COVID-19."

The study did not receive specific funding. The authors have reported no relevant financial relationships.

Lancet. Published online September 17, 2020. Full text

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