The researchers found long-term exposure to fine particulate matter from industrial pollution could double the risk for seniors of requiring hospitalization for pneumonia. (J.P. Moczulski/Canadian Press)

Exposure to high levels of pollutants from car exhaust and industrial air pollution over the long term may be linked to a doubling of risk of hospitalization for pneumonia among seniors, a Canadian study suggests.

Researchers from McMaster University in Hamilton looked at 365 older adults in the city who had been hospitalized with confirmed pneumonia between 2003 and 2005, and a randomly selected control group of 494 people without pneumonia.

Breathing two air pollutants for more than 12 months was associated with a doubling in risk of hospitalization from pneumonia — a leading cause of sickness and death among older adults.

"What we found was that individuals who developed community-acquired pneumonia were more likely to have long-term exposure to nitrogen dioxide [from vehicle exhaust] and they were twice more likely to be hospitalized," said principal investigator Dr. Mark Loeb, an infectious disease specialist at McMaster.

Specifically, people with long-term exposure to nitrogen dioxide had 2.3 times the risk for hospitalization with pneumonia, the team reported in the Jan. 1 issue of the American Journal of Respiratory and Critical Care Medicine.

They researchers also looked at another pollutant known as fine particulate matter of less than 2.5 micrometres, which comes mainly from smokestacks at industrial plants. The study took place in Hamilton's north end, where there is an industrial steel-making complex.

Using data from air-quality monitoring stations, the researchers found those with long-term exposure to fine particulate matter showed 2.26 times the risk of hospitalization with pneumonia.

Immune system interference

Exposure to another air pollutant, sulphur dioxide, was not associated with increased risk of hospitalization.

It could be that exposure to pollutants increases susceptibility to severe pneumonia — which is most often caused by a bacterial infection — by interfering with immune system defences that protect the lungs.

"We postulate that there might have been effects on the innate immune system, that is, these air pollutants would affect the ability of the lungs to clear pathogens," Loeb said.

The findings highlight how long-term exposure to air pollution can affect respiratory infections, the researchers said. Previously, air pollution has been recognized as a risk factor for exacerbating asthma and chronic pulmonary disease.

"It also emphasizes the need to monitor emissions from vehicles, given that ground level [nitrogen dioxide] is derived predominantly from traffic," the study's authors concluded.

"When a number of studies show there's a deleterious impact, that's what can drive policies in terms of standards on vehicle emissions," Loeb added.

With files from The Canadian Press