Air pollution linked to bronchitis in preschoolers
UC Davis study points to need for greater controls on sources of pollutants
In one of the first studies to examine air pollution in relation to infant and early childhood health, a UC Davis researcher has discovered a strong link between exposure to components of air pollution and acute bronchitis diagnoses in preschool-aged children. Those components — polycyclic aromatic hydrocarbons, or PAHs — contribute to air pollution from a variety of sources, including coal burning, vehicle exhaust, wood-burning stoves, tobacco smoke and grilling food.
The Czech connection
Led by UC Davis environmental epidemiologist Irva Hertz-Picciotto, the Czech Early Childhood Health Study involved 1,133 children from birth to 4.5 years of age born in two districts of the Czech Republic between 1994 and 1998. One of those districts, Teplice (pronounced Tuh-PLEET-zuh), is known for its high levels of air pollution. The other, Prachatice (pronounced prah-kuh-TEET-zuh), has much lower levels of air pollution.
Hertz-Picciotto and colleagues compared information on medical diagnoses of lower respiratory illnesses such as bronchitis, croup, pneumonia and asthma with detailed data on air quality. The findings revealed a significant increase in diagnoses of acute bronchitis when children aged 2 to 4.5 were exposed to medium-to-high levels of PAHs for 30 consecutive days.
Increase in acute bronchitis diagnoses
“This is the first large-scale, comprehensive study looking at early childhood respiratory infections and the constituents of today's air pollution,” said Hertz-Picciotto, a UC Davis professor of epidemiology and lead author of the study. “We found that polycyclic aromatic hydrocarbons have a significant effect on the lung health of children in the study, in particular in increases in acute bronchitis diagnoses for toddlers and preschoolers. We saw the biggest impact on children old enough to play outside, while infants were affected but not quite as much.”
Wood, coal, diesel or tobacco
Scientists classify the components of air pollution as either particles or a variety of chemical compounds. Whereas a number of studies have examined particles, sulfur dioxide and ozone, very little research in human populations have addressed PAHs, which result from the incomplete combustion of carbon-containing fuels such as wood, coal, diesel or tobacco. Current environmental regulations in both the United States and Europe focus on controlling particulate emissions.
“Our work strongly suggests that regulators consider efforts to curb PAHs as well. Reducing particles may also reduce chemical emissions but the impact will depend on what control measures are taken. When it comes to children's lung health, we need to take steps to reduce all risk factors,” Hertz-Picciotto said. “Additional precautions particularly pertinent here in California to protect children from the harmful effects of PAHs include not smoking around children and using alternatives to wood for heating homes in the winter.”
Hertz-Picciotto and colleagues collected standardized medical records and information from parent questionnaires about work history, demographics, lifestyle, and reproductive and medical histories. Follow-up information was collected once for each child at the age of 3 for those born between 1994 and 1996 and at age 4.5 for those born in 1997 or 1998.
Air quality samplings
— Irva Hertz-Picciotto, professor and lead author of the study
At the same time, the team collected detailed air quality sampling data on levels of particulate and PAH air pollution in the regions. PAHs are particularly difficult and expensive to measure. Hertz-Picciotto and her researchers had unique access to daily measures of air quality — both particulate matter and PAHs — for winter months, while measures were taken at three-day intervals in the fall and spring and six-day intervals in the summer when these air pollutants are at their lowest. As a result, the volume and detail of medical and environmental data used in the analysis is uniquely robust and allowed researchers to control for a whole host of potentially confounding factors.
“It is an impressive amount of very complete data, giving us a rare opportunity to look at the impact of air pollution on the health of young children and the actual components comprising that pollution,” Hertz-Picciotto explained. “We were able to correct for everything from duration of breast feeding to smoking in the home to average daily temperature.”
The PAH levels identified in the Czech Republic are comparable to those found in Western Europe and the United States. Some rural areas of California, for example, see sharp increases of PAHs in the winter due to the burning of wood stoves for heat. Likewise, increases in bronchitis in the Czech children were seen in the winter months when air quality was the poorest.
Health care in Czech Republic
In addition to comparable air pollution profiles to those in the United States, the Czech Republic was an ideal study site for evaluating physician-diagnosed illnesses because of its open public-health infrastructure. All citizens of the Czech Republic are entitled to free, readily available medical care. Families remain with one pediatrician for all of their children from birth to adulthood. For researchers, this meant access to thousands of standardized medical records and participation rates of more than 95 percent by those asked to fill out follow-up questionnaires.
“There are virtually no barriers to receiving health care in the Czech Republic and virtually all families develop strong, lasting relationships with their pediatricians and nurses,” Hertz-Picciotto said. “This definitely helped keep participation levels high.”
Bronchitis occurs when the inner walls that line the main air passageways of the lungs become infected, inflamed and narrowed. It usually follows a cold or the flu. The result is a persistent, productive cough, shortness of breath and chest tightness and pain. Some cases of bronchitis can be treated by antibiotics but most are due to viruses, for which there are no treatments. Acute bronchitis is among the top 10 conditions for which patients seek medical care. It is a major contributor to missed school for children and workdays for parents who stay home with them. Estimated costs for evaluating and treating this illess are between $200 and $300 million each year.
“Air quality negatively impacts children's health and has a definite economic impact on health systems and families,” Hertz-Picciotto said.
Scientists have yet to discover the biological mechanism by which air pollution in general and PAHs in particular contribute to lower respiratory illnesses. Hertz-Picciotto theorizes that the chemicals in air pollution may have an impact on the immune system.
“It's possible that increased inflammation of the airways due to the PAH exposure compromises the immune system and makes it easier for viruses to take hold,” she explained. “We need more basic science to answer this question.”
In the meantime, Hertz-Picciotto and her colleagues will continue to investigate the impact of other air pollution components and their potential connections to childhood illnesses using the Czech data sets. They will also be looking at whether prenatal exposure to air pollution leads to increased susceptibility to illness, such as asthma and hay fever, later in life.
Results of the study are published in the October 2007 issue of Environmental Health Perspectives and can be downloaded at www.ehponline.org. Funding for the research was provided by the Czech Ministry of Environment, U.S. Environmental Protection Agency, U.S. Agency for International Development, Commission of the European Community, Health Effects Institute and National Institute of Environmental Health Sciences. Hertz-Picciotto's research team included an international group of scientists from the Czech Republic, Germany, UC Davis and the University of North Carolina, Chapel Hill.