Flu-Linked Respiratory Infections Cause Substantial Annual Effect

Lower respiratory tract infections (LRTIs) linked to influenza were responsible for an estimated 145,000 deaths worldwide in 2017, according to an analysis from the Global Burden of Disease Study (GBD).

The mortality rate from influenza-linked LRTIs was highest among adults older than 70, at 16.4 deaths per 100,000 people. Eastern Europe and the Caribbean had the highest mortality rate among all ages, at more than 5 deaths per 100,000 people.

In the US, the influenza LRTI mortality rate for all ages was comparable to many countries in Western Europe. However, the LRTI incidence among all ages was lower than in most Western European countries.

Overall, the study estimated influenza LRTIs accounted for almost 9.5 million hospitalizations and 81.5 million hospital days globally in 2017.

“One of the main messages of our analysis is that there is substantial health-loss attributable to influenza LRTIs, and that they are avoidable,” senior author Robert C. Reiner, Jr, PhD, ssistant professor of Health Metric Sciences at the University of Washington, School of Medicine, told MD Magazine®. “Reducing exposure to influenza, through vaccines or other modifiable risk factors, would help make populations healthier and reduce stress on healthcare systems.”

LRTIs are the leading cause of infectious disease mortality worldwide, and such infections cause more deaths than tuberculosis and HIV combined, the authors noted. In 2016, LRTIs were responsible for more than 2.5 million deaths and were the fifth-leading incident infectious disease globally.

In the GBD study, Reiner and his team attempted to quantify the causes of health-loss over time for every country and age group. They sought to include all available data—through systematic reviews of scientific literature, surveys, and healthcare records—that describe disease epidemiology.

Reiner noted that the study used statistical modeling to produce its estimates, even in locations without data.

From its results, the GBD showed it differs from reports produced by the US Centers for Disease Control and Prevention. While the CDC attempts to measure the total respiratory infection burden associated with influenza, the GBD study sought to quantify the LRTI burden attributable to influenza. The GBD study also defined LRTIs as either pneumonia or bronchiolitis.

“In our study, we report the number of deaths, hospitalizations, and episodes of LRTI that would be averted if there were no exposure to influenza,” Reiner explained.

In their analysis, the team relied on almost 100 influenza and respiratory experts to estimate the influenza-attributable burden of LRTIs globally for both sexes and all ages in 2017.

“To the best of our knowledge, no other study has produced estimates for such specific demographic categories,” the authors wrote.

When asked about the US findings, Reiner said that the lower incidence of LRTI among all ages compared to Western Europe suggests that the case fatality ratio is lower in the US compared to other high-income locations. He noted that this may indicate better treatment or a difference in the age distribution of cases and episodes.

Overall, the results showed that while the rates of LRTIs attributable to influenza are lower among individuals aged 15 to 65 than in younger or older populations, the proportion of all LRTIs due to influenza was actually highest in this age group.

“Recognizing age trends could be useful in designing interventions,” Reiner said.

He added that the GBD study is a departure from typical flu research since many influenza studies focus on the pandemic potential of the virus and explore strategies to prevent and mitigate future epidemics. In contrast, the GBD study shows that resources should be prioritized to help prevent LRTI-related deaths and hospitalizations.

“Seasonal influenza is responsible for substantial mortality, disability, and economic disruption,” the authors wrote. “Appropriate efforts to decrease this burden require timely and reliable estimates of the full spectrum of disease.”

The estimates provided by the GBD study also provide motivation to act.

“Our approach allows us to interpret our results such that if we were to reduce exposure to influenza to none, there would be 145,000 fewer deaths in 2017,” Reiners said. “With this knowledge and context, public health officials, clinicians, and policy-makers can develop strategies, like influenza vaccines or smoking cessation programs, that will save lives and reduce health-loss due to influenza LRTIs.”

Furthermore, the study also might spark new approaches to fighting flu. For instance, diagnostics for respiratory infections, such as polymerase chain reaction on nasopharyngeal swabs, may help to identify influenza in LRTIs, he said. Accurate information about the presence of influenza could better guide treatment and help to strengthen and refine the global influenza burden estimates.

“Resources need to be prioritized to help prevent the estimated 145,000 influenza lower respiratory tract infection deaths that occur every year,” Reiner concluded.

The study, titled, “Mortality, Morbidity, and Hospitalisations Due to Influenza lower respiratory tract infections, 2017: an analysis for the Global Burden of Disease Study 2017,” was published online in The Lancet Respiratory Medicine.