Obesity Increases Risk of Influenza A Spread and Severity

Impact of Obesity on Influenza A Virus Shedding

Study Overview

A recent study published in The Journal of Infectious Diseases indicates that obesity may facilitate the spread of the influenza A virus by prolonging the duration of virus shedding in infected adults. The ongoing global obesity epidemic has been associated with a rise in various chronic diseases, and this research suggests it may also affect the progression of infectious diseases like influenza. Individuals with obesity are generally at a heightened risk for severe complications related to the flu virus, a risk that escalates with age. This can be attributed to the significant strain obesity places on the immune system, leading to chronic inflammation over time.

Understanding Viral Shedding

Viral shedding refers to the process in which viruses escape from infected human cells after replication. These new viral particles can then spread to other cells or be expelled from the body through actions like sneezing or coughing. Importantly, individuals infected with a virus may still shed it even if they exhibit few or no symptoms, thus posing a risk of unknowingly infecting others.

Factors influencing the duration of viral shedding include age; for instance, children are known to shed the flu virus for longer periods than adults. Researchers in Britain and Nicaragua hypothesized that chronic inflammation resulting from obesity could extend the duration of viral shedding. They aimed to determine whether obese individuals shed the flu virus longer than their non-obese counterparts, publishing their findings in the Journal of Infectious Diseases.

Research Methodology

The study monitored 1,783 Nicaraguan participants across 320 households during three flu seasons from 2015 to 2017. The sample included 340 children aged 0-4 years, 631 children aged 5-17 years, and 812 adults aged 18-92 years. The prevalence of obesity (defined as a BMI greater than 30 kg/m²) was relatively low among children (2-9%) but soared to 42% in adults.

When individuals exhibited flu symptoms—such as a fever of 100°F (37.8°C), sore throat, runny nose, or cough—all household members were monitored for 10-13 days, even if they showed no symptoms. Testing revealed that 87 participants were infected with influenza A and 58 with influenza B, with obese individuals typically exhibiting more severe symptoms.

Findings on Viral Shedding Duration

The analysis of nose and throat swab results provided insights into the duration of viral shedding. In children aged 0-4 years, the low prevalence of obesity precluded assessment of its impact on shedding duration. Similarly, in children aged 5-17 years, obesity did not appear to affect shedding duration, potentially due to the absence of chronic inflammation.

Conversely, in adults, viral shedding was significantly longer in those with obesity. Specifically, obese adults with at least two influenza A symptoms shed the virus for 5.2 days, compared to 3.7 days for non-obese adults—a 42% increase. For obese adults with one or no symptoms of influenza A (excluding fever), the duration of shedding extended by 104%, from 1.6 days in non-obese adults to 3.2 days. It is worth noting that obesity did not influence the shedding duration of influenza B.

Variations in Children’s Viral Shedding

Although no direct correlation was found between obesity and viral shedding duration in children, significant differences emerged within the cohort. Young children (0-4 years) shed the virus for 40% longer periods, while older children (5-17 years) shed it for 30% longer than adults.

Future Research Directions

The authors of the study emphasized the need for further research to explore how obesity impacts the transmission of Influenza A in the broader community rather than solely within households. Future studies should aim to accurately determine the end of the shedding period and quantify the viral load released during this time. Such investigations could illuminate the connections between obesity, chronic inflammation, and infectious diseases.

Despite some limitations, this study provides compelling evidence that obesity prolongs the duration of influenza A shedding in adults, even when they show no visible symptoms. Considering the global implications of obesity, particularly in low-income countries, prioritizing interventions and prevention strategies against obesity is critical.

References

Maier HE, et al. Obesity increases the duration of influenza A virus shedding in adults. J Infect Dis. 2018. Available at doi:10.1093/infdis/jiy370.
Obesity extends duration of influenza A virus shedding. Retrieved from https://www.nih.gov/news-events/news-releases/obesity-extends-duration-influenza-virus-shedding, accessed 20 August 2018.