Short-term Air Pollution Exposure Tied to Respiratory Infections

Diana Mahoney

April 13, 2018

Short-term spikes in air pollution are linked to an increased risk for respiratory infections, particularly among young children, according to research published online April 13 in the American Journal of Respiratory and Critical Care Medicine.

Benjamin D. Horne, PhD, from the Intermountain Medical Center Heart Institute in Salt Lake City, Utah, and colleagues designed the case-crossover study to assess the potential relationship between airborne fine particulate matter, referred to as PM2.5, and respiratory conditions in a large sample of Utah residents.

Overall, they found statistically significant associations between higher PM2.5 exposures and elevated acute lower respiratory infections (ALRIs) in young children (0 - 2 years), older children (3 - 17 years), and adults (18 years and older).

The researchers analyzed data on residents of Wasatch Front, an urban corridor in the North Central part of Utah, who were treated for ALRIs at Intermountain Healthcare hospitals or clinics between 1999 and 2016. Because of its geography, Wasatch Front is vulnerable to periodic weather inversions that trap emissions, causing air pollutants to accumulate.

Previous research has shown that ALRIs, as well as many other conditions, including asthma and chronic obstructive pulmonary disease exacerbations, thrombosis, myocardial infarction, heart failure exacerbations, and mortality, may be associated with greater exposure to elevated ambient air pollution, including PM2.5 and other air pollutants.

However, the evidence linking short-term PM2.5 elevation with these infections "is weak and contradictory," the authors report. Young children may be especially vulnerable to the ill effects of high PM2.5 concentrations, they write, noting prior evidence linking both short- and long-term exposure to PM2.5 to hospitalization of newborns and infants.

Therefore, the researchers aimed primarily to describe the relationship between short-term PM2.5 increases and ALRI diagnoses in patients younger than 2 years.

A total of 146,397 patients with ALRI were included in the analysis, including 112,567 (76.9%) age 0 to 2 years of age, 17,558 (12%) age 3 to 17 years, and 16,272 (11.1%) age 18 years or older.

Using recorded weather and air quality data for 1999 to 2016, the researchers generated PM2.5 exposure estimates and linked them with the clinical data in a conditional logistic regression model. The likelihood of an ALRI diagnosis across the entire sample over the course of 1 month increased between 15% and 23% for each additional 10 µg/m3 of PM2.5.

"The odds of ALRI peaked about 3 weeks after the elevation in ambient air pollution occurred, but was statistically significantly elevated within a lag time of as little as 1 week afterwards," the authors write.

The odds of an respiratory syncytial virus (RSV) diagnosis in particular was higher following a PM2.5 increase beginning 2 weeks after the pollution increase and peaking at 3 weeks.

"As expected, RSV infection and bronchiolitis were primarily problems for the very young ages 0-2 years," the authors write. "Bronchiolitis deserves special attention given the disproportionate magnitude of the effect on healthcare utilization, where 77% of subjects in this study belonged to that very young age group."

Similarly, the likelihood of an influenza diagnosis, which was most notable among older children and adults, rose following a PM2.5 increase, although the higher odds tended to peak earlier, the authors write. "[T]he findings that elevated PM2.5 concentrations were associated with more diagnosed and laboratory-confirmed influenza, even in older children and adults, may also be important given that previous studies of adults have observed higher risk of mortality due to influenza/pneumonia associated with long-term exposures to PM2.5. These findings further suggest that PM2.5 exposures contribute to susceptibility and/or severity of infection."

Looking at the association between PM2.5 increases and ALRI by encounter type, "the effects of PM2.5 were not only statistically significant for outpatient, emergency, and inpatient settings, but the associated risk was greater for subjects seen in an emergency setting than for outpatient visits, and was especially high for those with inpatient hospital admission," the authors write. This finding suggests that the pollutant levels may affect the severity of infection, they note.

In the all-cause mortality analysis, 107 patients died within 30 days of their ALRI event, including 17 (0.015%) in the 0 to 2 years group, 9 (0.051%) in the 3 to 17 years group, and 81 in the adult group (0.498%).

Although the study does not provide specific insight into the mechanisms driving the association between air pollution and ALRI rates, the findings add to a growing body of evidence suggesting that PM2.5 exposure may contributes to susceptibility to RSV and influenza, exposure to these pathogens, infection, and severity of infection, the authors write.

"Additional research regarding the causal connections of ambient air pollution and ALRI is needed, as well as the consideration of RSV immunization for the public health," the authors stress. "Community and health system approaches, such as predicting hospital staffing needs, coordinating timely medical supplies delivery, and community alerting to expected times of higher infectious susceptibility, may be possible and useful for ameliorating the effect of higher ambient PM2.5 levels on adverse health outcomes, improving health and healthcare quality, and reducing costs."

The authors have disclosed no relevant financial relationships.

Am J Respir Crit Care Med. Published online April 13, 2018. Abstract

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