According to newly published research, even the briefest increase in airborne fine particulate matter PM2.5, pollution-causing particles that are about 3% of the diameter of human hair, is associated with the development of acute lower respiratory infection (ALRI) in young children. 

Increases in PM2.5 levels also led to increased doctor visits for these lung infections. The groundbreaking study, "Short-Term Elevation of Fine Particulate Matter Air Pollution and Acute Lower Respiratory Infection," is the largest to date on this health concern, involving more than 100,000 patients.

"The most important finding of this study is that infectious processes of respiratory disease may be influenced by particulate matter pollution at various levels," said lead author Benjamin Horne. "The exact biological implications of the study's findings require further investigation."

Dr. Horne and colleagues studied 146,397 individuals who were treated for ALRI between 1999 and 2016 at Intermountain Healthcare facilities throughout Utah's Wasatch Front region.

The Wasatch Front is approximately 80 miles long and 10-20 miles wide, bordered on both sides by mountains. It consists primarily of suburbs, but also includes the cities of Salt Lake City, Ogden and Provo/Orem.

The primary aim of the study was to determine if there was an association between these fine particulates and ALRI in very young children, with a secondary objective of finding the same associations for older children, adolescents, and adults.

The research team found ALRI associated with elevated levels of PM2.5 in both children and adults — even in newborns and toddlers up to age two, who represented 77% (112,467) of those who had an ALRI diagnosis. Nearly 60% of U.S. children live in counties with PM2.5 concentrations above air quality standards.

This study was performed in a location where the average daily PM2.5 level is lower than places like Los Angeles and New York. Due to the topography of the region, though, air pollution may become trapped in the high mountain valleys of the Wasatch Front — especially during temperature inversions, which typically occur in the winter months.

When PM2.5 becomes trapped in the valleys, this often leads to sharp increases in PM2.5 to levels considered to be unhealthy (>35 micrograms per cubic meter, and at times approaching 100 ug/m3).

"In many places that have higher average PM2.5, the PM2.5 level does not vary as much as it does on the Wasatch Front, so it is not clear how this study's findings may transfer to those locales where the air pollution exposure is higher over the long term, but short-term spikes do not occur," said Dr. Horne.

Fifty to 90% of bronchiolitis cases are caused by the respiratory syncytial virus (RSV), which is the most common cause of hospitalization in the first two years of life. Sixty-four percent of individuals studied had a diagnosis of bronchiolitis.

This could lead to longer periods of ALRI symptoms or more severe symptoms requiring a higher intensity of medical care for the infected individual. It may also be those periods of acute increases in PM2.5 lead people to stay indoors more where they are in closer contact with others who carry infectious agents and can transmit the infection to them."

"The practical implications for prevention of ALRI and amelioration of symptoms include that when an acute increase in the level of PM2.5 occurs, people may be able to prevent infections or decrease ALRI symptom severity or duration by reducing their exposure to the air pollution," said Dr. Horne.

"Furthermore, a substantial elevation in PM2.5 may also serve as a nudge that reminds or alerts people to avoid areas and activities where other people may share an infection with them, to not touch their face with dirty hands, to be vigilant about washing their hands when reasonably possible or prudent, and to engage in other preventive behaviors that are known to reduce infection risk."