In addition to obesity's known impact on flu severity—complications including hospitalization and even death—new findings from investigators at the University of Michigan School of Public Health suggest that obesity may play a significant role in the transmission of the influenza virus. Findings from the new study, published today in The Journal of Infectious Diseases through an article titled “Obesity Increases the Duration of Influenza A Virus Shedding in Adults,” suggests 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.
Using data gathered from approximately 1,800 people in 320 households in Managua, Nicaragua, the University of Michigan researchers investigated the effect of obesity on the duration of viral shedding over three influenza seasons from 2015 to 2017. Remarkably, the researchers found that obese adults with flu symptoms and laboratory-confirmed influenza shed influenza A virus for 42% longer than adults with flu who were not obese. Moreover, among obese individuals infected with flu who were only mildly ill or had no symptoms, the difference was even greater—these obese adults shed influenza A virus for 104% longer than non-obese adults with flu.
“This is the first real evidence that obesity might impact more than just disease severity, it might directly impact transmission as well,” remarked senior study investigator Aubree Gordon, Ph.D., assistant professor of epidemiology at the University of Michigan School of Public Health.
The duration of viral shedding was determined by tests of nose and throat samples, which detected the presence of influenza virus RNA but did not indicate whether the viruses were infectious. Additional research, now underway, will help determine if the flu virus shed for longer periods by obese individuals is indeed infectious and can spread the illness to others.
Additionally, the differences seen in the duration of viral shedding were limited to influenza A viruses, one of two types of flu viruses that can cause epidemics in humans. The Michigan researchers found no association with obesity and the duration of shedding of influenza B virus, which typically causes less serious illness in adults and does not cause pandemics. Obesity also did not appear to impact the duration of viral shedding among children included in the study.
With rates of obesity rising around the world, the new findings, if supported by future studies, suggest that obesity may play an increasingly important role in flu transmission. In a related editorial commentary that appears with the new study in The Journal of Infectious Diseases, Stacey Schultz-Cherry, Ph.D., faculty member, St. Jude Children'ts Research Hospital and deputy director, World Health Organization collaborating centre for studies on the ecology of influenza in animals and birds, noted several potential public health implications, including increased opportunities for influenza to spread in some populations.
“It is therefore even more important to develop effective strategies to prevent and control influenza, especially in the overweight and obese population, which could be challenging because of the poor vaccine responses in this population,” wrote Dr. Schultz-Cherry, who was not involved with the study. “With increasing focus on the development of a universal influenza vaccine, improved protection from influenza is on the horizon. The question remains whether these approaches will not only protect this target population but also reduce viral shedding duration.”