The association between nitrogen oxides exposure and acute bronchitis was found to increase with age in the first two years. In other words, those between 1 and 2 years showed a stronger association compared to those below 1 year of age.
A similar trend was not observed in children between 2 and 4-½ years of age, said study lead author Rakesh Ghosh, a postdoctoral researcher with the UC Davis Department of Public Health Sciences.
"Ambient nitrogen oxides exposure and early childhood respiratory illnesses," is published online this week in the journal Environmental International.
"Acute bronchitis is relatively common in preschool children," said Irva Hertz-Picciotto, professor and chief, Division of Environmental and Occupational Health in the UC Davis Department of Public Health Sciences and the study's principal investigator.
"We found an exposure of approximately 35 micrograms per cubic meter of nitrogen oxides increased incidence of acute bronchitis by about 30 percent," Hertz-Picciotto said.
Acute bronchitis involves inflammation of the main airways to the lungs and often occurs after a viral infection. It causes cough, fatigue and low-grade fever, and may be followed by several weeks of a dry, nagging cough. About 20 percent of deaths in children under 5 years are due to acute lower-respiratory illness.
Nitrogen dioxide is known to be a deep lung irritant and is regulated by the U.S. Environmental Protection Agency (EPA): The standard is no more than 188 micrograms per cubic meter for any one-hour average and no more than 100 micrograms per cubic meter as an annual average.
The study was conducted in two districts in the Czech Republic, Teplice and Prachatice, where ambient levels of nitrogen oxides were regularly monitored. The mixture of gases, consisting mainly of nitrogen dioxide and nitric oxide, are pollutants that result from burning fossil fuels in industrial installations such as power plants and automobiles.
For the study, the researchers obtained monitored daily ambient nitrogen-oxide levels starting in May 1994 through June 2003. A total of 1,133 children were followed from birth up to 4-½ years of age. The children's respiratory health information was obtained from medical records and additional information was collected using maternal questionnaires.
The researchers also examined what fuels were used in the children's homes for heating and cooking, i.e. gas, electricity or coal, and other potential exposures, such as second-hand cigarette smoke. The increased association found solely from air pollution persisted even after accounting for these other factors.
"Although our results are not directly comparable, because the current regulatory standards are for nitrogen dioxide and we investigated a mix of nitrogen oxides, the standards are much higher than the levels associated with increased incidence of respiratory illnesses in this study. This means that levels considered safe actually may pose a risk of elevated rates of respiratory disease in young children," Hertz-Picciotto said.
Other study authors include Jesse Joad, associate dean of Diversity and Faculty Life at the UC Davis School of Medicine; Ivan Benes with the Institute of Hygiene in Teplice, Czech Republic; and Miroslav Dostal and Radim J. Sram, both with the Institute of Experimental Medicine, Academy of Sciences, the Czech Republic in Prague.
The study was funded by the Czech Ministry of the Environment.
The UC Davis School of Medicine is among the nation's leading medical schools, recognized for its research and primary-care programs. The school offers fully accredited master's degree programs in public health and in informatics, and its combined M.D.-Ph.D. program is training the next generation of physician-scientists to conduct high-impact research and translate discoveries into better clinical care. Along with being a recognized leader in medical research, the school is committed to serving underserved communities and advancing rural health. For more information, visit UC Davis School of Medicine at medschool.ucdavis.edu.
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