Obesity Increases Risk of Influenza Transmission, Disease Severity

By Brenda L. Mooney, /alert Contributor
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While it has long been known that obesity increases a patient’s risk for severe complications from influenza, including hospitalization and even death, a new study discussed how excess weight could also affect flu transmission.

The study published in The Journal of Infectious Diseases found that obese adults infected with flu shed the virus for a longer time than adults who are not obese, potentially increasing the opportunity for the infection to spread to others.

Man with flu. Source: Getty

University of Michigan-led researchers suggested that high rates of obesity appear to be complicating efforts to slowdown transmission of influenza, by increasing the opportunity for the infection to spread to others.

"This is the first real evidence that obesity might impact more than just disease severity," said senior study author Aubree Gordon, MPH, PhD, of the University of Michigan School of Public Health. "It might directly impact transmission as well."

For the study, investigators at the effect of obesity on the duration of viral shedding within household transmission studies in Managua, Nicaragua, over three flu seasons from 2015 to 2017. They found that symptomatic obese adults shed influenza A virus 42% longer than non-obese adults (adjusted event time ratio [ETR], 1.42; 95% confidence interval [CI], 1.06–1.89).

“Even among paucisymptomatic and asymptomatic adults, obesity increased the influenza A shedding duration by 104% (adjusted ETR, 2.04; 95% CI, 1.35–3.09),” study authors pointed out. “These findings suggest that obesity may play an important role in influenza transmission.”

The researchers theorized that chronic inflammation caused by obesity, as well as increasing age, could play roles in extended viral shedding, which puts other at risk for infection.

During the study period, 1,783 people from 320 households in Managua were monitored during the three flu seasons. During that time period,  87 of the participants became ill with influenza A and 58 with influenza B.

Researchers used body mass index (BMI) to determine obesity in 2% of participants up to age 4, 9% of those  ages 5-17, and 42% of adults.

Results indicate that 62 obese adults with two or more symptoms of influenza A shed the virus in an average of 5.2 days compared to 3.7 days for non-obese adults. At the same time, 25 obese adults with one or no symptoms of influenza A shed the virus for an average of 3.2 days vs.1.6 days.

Obesity played no role in increased viral shedding duration in children ages 5-17 or for adults with influenza B, according to the report.

“While previous studies identified obesity as a risk factor for severe influenza outcomes [1, 2], we showed that obesity also affects less severe outcomes by significantly increasing the duration of influenza A virus shedding in adults,” study authors conclude. “Further, we found that, even in asymptomatic or mildly ill individuals, obese adults shed influenza A virus for a longer duration than nonobese adults. This has important implications for influenza transmission.”