Prolonged exposure to higher levels of the pollutants found in car exhaust fumes and industrial air pollution can lead to hospitalization for pneumonia in adults aged 65 and older, a new study has found.

Mark Loeb from McMaster University and colleagues assessed the effect of long-term exposure to nitrogen dioxide and sulfur dioxide, both found in motor vehicle emissions, and fine particulate matter, found in industrial air pollution, on the risk of hospitalization for pneumonia in older adults.

"Our study found that among older individuals, long-term exposure to traffic pollution independently increased their risk of hospitalization for pneumonia," said Loeb.

"We propose that exposure to air pollution may have increased the individuals' susceptibility to pneumonia by interfering with lung immune defenses designed to protect the lung from pathogens," Loeb added.

The researchers recruited 365 older adults from Hamilton who had been hospitalized with radiologically confirmed pneumonia between July 2003 and April 2005. Control subjects randomly selected from the same neighbourhoods as the patients were also enrolled in the study.

They used structured interviews to collect health data from participants and compared the two groups' exposures to nitrogen dioxide, sulfur dioxide and fine particulate matter of less than 2.5 mm using data from air-quality monitoring stations and land-use regression models.

The researchers found that exposure for more than 12 months to higher levels of nitrogen dioxide and fine particulate matter of less than 2.5 mm more than doubled the risk of hospitalization for pneumonia in adults aged 65 and older. Exposure to sulfur dioxide was not associated with an increased risk of hospitalization.

"The results of this study highlight the important health impact that long-term exposure to ambient air pollution can have on respiratory infections," Loeb said.

The results are to be published in the January 1, 2010, issue of the American Journal of Respiratory and Critical Care Medicine.