Lower respiratory tract infections remain leading infectious cause of death worldwide

Lower respiratory infections accounted for 2.74 million deaths in 2015, making them the fifth leading cause of death and leading infectious cause of death worldwide, according to data from the Global Burden of Disease 2015 study.

The estimates are similar to those previously reported in the Global Burden of Disease (GBD) 2013 study, according to Christopher Troeger, MPH, of the Institute for Health Metrics and Evaluation, University of Washington, Seattle, and colleagues.

“The findings call for renewed efforts to control and prevent LRIs across all age groups,” the researchers wrote in Lancet Infectious Diseases.

For the study, the researchers used modeling and meta-regression platforms to estimate LRI incidence, mortality and morbidity in 195 countries from 1990 to 2015. They specifically assessed the burden of Streptococcus pneumoniae (pneumococcal pneumonia), Haemophilus influenzae type b (Hib), influenza and respiratory syncytial virus (RSV).

More than 291 million (95% uncertainty level, 276.3 million-307 million) LRI episodes occurred in 2015. Among them, 101.8 million (95% UI, 90 million-114.4 million) were reported in children aged younger than 5 years. The most common etiology was pneumococcal pneumonia, which was responsible for 1,517,388, or 55.4%, of all LRI deaths.

In addition to 2.74 million deaths (95% uncertainty level, 2.50 million-2.86 million), Troeger and colleagues estimated that LRIs caused 103 million disability-adjusted life-years (DALYs; 95% UI, 96.1 million-109.1 million).

“Our results suggest that LRIs were the second-leading cause of DALYs globally in 2015 after ischemic heart disease,” they wrote.

Children aged younger than 5 years were disproportionately affected by LRIs, accounting for nearly 60% of DALYs (60.6 million) in 2015, according to the researchers. In addition, LRIs accounted for 12.1% of deaths and were the third leading cause of mortality in this population after preterm birth and neonatal encephalopathy. However, mortality rates due to LRIs were higher among adults aged 70 years or older (1.27 million vs. 703,918).

From 2005 to 2015, the number of deaths caused by LRIs decreased 3.2% (95% UI, –0.4 to 6.9) among all age groups, and 36.9% (95% UI, 31.6-42) among children aged younger than 5 years. During the same period, LRI DALYs increased 18.9% among adults aged 70 years and older, particularly in low-socio-demographic index regions, where DALYs increased 25%.

The leading risk factors for LRI DALYs in 2015 included childhood undernutrition (44.6% of DALYs), as well as household (35.8% of DALYs) and ambient air pollution (27.5% of DALYs). However, global improvements in childhood undernutrition and air pollution exposure resulted in an 8.9% and 4.3% decrease in the overall prevalence of LRI DALYs, which declined 23.8% from 2005 to 2015. The researchers also attributed the reduction in LRI DALYs to Hib vaccine use.

“At the global level, the [population attributable fraction (PAF)] of Hib on LRI deaths decreased 37.8% between 2005 and 2015, reflecting the expanded use and introduction of the vaccine during this time, particularly in countries that received support from Gavi,” they wrote. “Despite the growing use of [the pneumococcal conjugate vaccine (PCV)], pneumococcal pneumonia mortality has not decreased significantly at the global level.”

Troeger and colleagues concluded that additional efforts to improve case management, expand PCV use and reduce childhood undernutrition and air pollution exposure are needed to further accelerate reductions in LRI disease burden.

In a related editorial, Cynthia G. Whitney, MD, of CDC’s Division of Bacterial Diseases and National Center of Immunization and Respiratory Diseases, noted that inadequate data on LRIs, particularly pneumonia, limits the ability for researchers to estimate the burden of these infections in every country.

“The numbers generated by the models presented by the GBD 2015 LRI Collaborators might have limitations, yet they paint a vivid picture of the progress still to be made in the prevention of pneumonia deaths,” she wrote. “These numbers also highlight the places where most deaths are occurring and, therefore, where interventions are most needed. Effective interventions for reducing pneumonia deaths are available, and a vaccine to prevent RSV infection could be available in the near future. With continued resources and attention, modeled estimates on pneumonia deaths, as well as actual numbers, can continue to decrease.” – by Stephanie Viguers

Disclosure: One study author reports receiving grants from the Bill & Melinda Gates Foundation. Whitney reports no relevant financial disclosures.