Patients’ body mass played a role in risk of hospitalization from the flu, as those who were either obese or underweight were more likely to be admitted, researchers found from Mexican data.
Morbidly obese adults (BMI values of 35 or higher) had a significantly higher risk of hospitalization than normal weight adults (BMI 18.5 to <25: OR 18.40, 95% CI 7.83-47.4, P<0.001), albeit with a wide confidence interval, reported John H. Beigel, MD, of Leidos Biomedical Research (a National Institutes of Health contractor) in Bethesda, Maryland, and colleagues.
Compared to normal weight adults, underweight adults (BMI <18.5: OR 5.20, 95% CI 1.67-16.01, P=0.005) and obese adults (BMI 30-35: OR 3.18, 95% CI 1.73-5.91, P<0.001) also had significantly higher risks of hospitalization, the authors wrote in Influenza and Other Respiratory Viruses.
They noted that BMI, as an independent risk factor for severe influenza, wasn’t “widely appreciated” until the 2009 pandemic. While there was no increase in rates of influenza-like illness in obese patients, they said, “early reports during the pandemic noted an association between severity of illness and obesity,” and several studies found a link between obesity and death due to pandemic influenza.
Prior research addressed an association between obesity and the flu, and the authors said other studies have found links between obesity and hospitalization from influenza-like illness, but none examined low BMI as a risk factor.
They examined data from an observational cohort study at five centers in Mexico from 2010 to 2014. Participants included anyone with an influenza-like illness (at least one respiratory symptom and either fever or one or more respiratory symptoms). BMI was calculated for adults age 19 and older. Nasopharyngeal swabs were collected and tested for influenza and other respiratory pathogens.
Overall, there were around 4,800 patients with complete data — about a third of whom were children and adolescents. There were 3,248 adult participants with a mean age of 41, about 36% of which were men.
A little under two-thirds of pediatric patients and about a third of adult participants were hospitalized. A little over 40% of all patients had severe influenza-like illness. About 16% tested positive for influenza, while over half tested positive for other viral respiratory pathogens.
The type of influenza also appeared to play a role, the authors found that compared to normal weight adults, obese and morbidly obese adults had a significantly higher risk of hospitalization with influenza A H1N1 than with influenza A H3N2 and B viruses.
For adults with other respiratory viruses, such as coronavirus, metapneumovirus, parainfluenza, and rhinovirus — there was a higher risk of hospitalization for underweight adults (OR 4.07, 95% CI 1.71-9.45, P=0.002) and morbidly obese adults (OR 2.78, 95% CI 1.66-4.65, P<0.001), the authors found.
One limitation is that it only included participants who sought medical care for influenza-like illness, and cannot be considered “a population-based study that can accurately assess the risk that body mass confers for infection,” the authors wrote.
They concluded that “clinicians should keep a patient’s body mass index in mind when evaluating risk and deciding on a course of treatment” for seasonal influenza infection and other respiratory viral infections.
This study was supported by the National Institute of Allergy and Infectious Diseases and Consejo Nacional de Ciencia y Tecnología, a NIAID contract with Westat Inc., and the National Cancer Institute.
The authors disclosed no conflicts of interest.