Obesity in adults associated with increased susceptibility to influenza A
Obesity in adults is associated with an increased risk for influenza A (H1N1) infection, according to a study published in Clinical Infectious Diseases. Researchers did not find the same association with H3N2 susceptibility.
“During the 2009 pandemic, obesity emerged as a risk factor for severe influenza. However, how obesity might affect influenza outcomes is less clear. One possibility is that obesity impacts severity — that is, obese people do not get influenza any more often, but when they get it, there is a higher rate of severe disease,” Aubree Gordon, PhD, a researcher in the department of epidemiology at the University of Michigan’s School of Public Health, told Healio.
“However, it is also possible that obese people are more likely to get influenza, that is they have influenza more often and this leads to the increase in the rate of severe disease,” Gordon said. “And of course, it may be a combination of the two.”
Gordon and colleagues performed a case-ascertained, community-based study of influenza transmission within households in Nicaragua to investigate whether obesity increases the likelihood of influenza infection and symptomatic infection.
Between 2015 and 2018, they enrolled 335 influenza A index cases and 1,506 of their household contacts. According to the study, obesity was associated with increased susceptibility to symptomatic H1N1 infection among adults (OR = 2.10; 95% CI, 1.08-4.06) but not among children. The researchers found that the association increased with age.
Additionally, the study showed that obesity was associated with an increased likelihood of symptoms (OR = 3.91; 95% CI,1.55-9.87) among adults with H1N1 infection. The study also showed that among middle-aged and older adult patients with obesity, there was a slight increase in susceptibility to any H1N1 infection (OR = 1.20, 95% CI, 0.62-2.34).
The researchers noted that obesity was not associated with increased H3N2 susceptibility or increased associated symptoms.
Gordon said it is still unknown why obesity is associated with increased susceptibility to H1N1 and not H3N2 infection, but that they hypothesize that it could be because adults have had exposure to H1N1 a limited number of times, and for most of them, only as obese adults.
She said the findings may help to determine the mechanism of how obesity affects influenza risk, which could help to target prevention or develop treatments.
“The clinical take-home message is that obese individuals may be more susceptible to influenza A H1N1,” Gordon concluded. “While it is very important for physicians to encourage influenza vaccination for everyone, it may be especially important to stress vaccination of obese individuals, particularly in seasons when influenza A (H1N1) predominates.”