Ann Arbor, MI—Because of their age and body mass index (BMI), people who are obese and older might inadvertently be putting others at risk if they contract influenza. Obesity, which increases influenza disease severity, also extends—by about 1.5 days—how long the influenza A virus is shed from infected adults, according to a new study.

The report in the Journal of Infectious Disease notes that past research has confirmed obesity increases the risk of severe complications and death from influenza virus infections, especially in older patients.

In this study, however, University of Michigan–led researchers looked at the effect of obesity on the duration of viral shedding within household transmission studies in Managua, Nicaragua, over three flu seasons (2015–2017).

They found that symptomatic obese adults shed influenza A virus 42% longer than nonobese 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 point out. “These findings suggest that obesity may play an important role in influenza transmission.”

The researchers posit 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.

In the study, 1,783 people from 320 households in Managua were monitored during the three flu seasons between 2015 and 2017. During that time period, 87 people became ill with influenza A and 58 with influenza B.

Researchers used BMI to determine obesity in 2% of participants up to age 4 years, 9% of those aged 5 to17 years, and 42% of adults.

Results indicate that 62 obese adults with two or more symptoms of influenza A shed the virus an average of 5.2 days compared with 3.7 days for nonobese 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 versus 1.6 days.

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

“While previous studies identified obesity as a risk factor for severe influenza outcomes, 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.”
 « Click here to return to Weekly News Update.