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Analyzing data collected from approximately 1,800 people in 320 households in Managua, Nicaragua, researchers investigated the effect of obesity on the duration of viral shedding over three influenza seasons from 2015 to 2017. Obese adults with flu symptoms and laboratory-confirmed influenza shed influenza A virus for 42 percent longer than adults with flu who were not obese.
Among obese individuals infected with flu who were only mildly ill or had no symptoms, the difference was even greater: Obese adults shed influenza A virus for 104 percent longer than non-obese adults with flu. 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.
The differences 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. 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.
Obesity can alter the body’s immune response and lead to chronic inflammation, which increases with age, in addition to making breathing more difficult and increasing the need for oxygen. These factors may help explain how obesity could affect influenza risk, severity, and transmission potential, the study authors note. The findings suggest that obesity may play an important role in the transmission of influenza.