In Shanghai, the world’s largest cotton textile producer, workers are breathing easier, thanks to a landmark Harvard School of Public Health-led study that turned 25 last fall. The study, which has helped tighten air-quality standards in factories across China, has also raised worker-safety concerns in industries from grain processing and animal confinement to particle-board manufacturing and biotechnology—all of which contaminate the air with vegetable- or animal-derived dusts.
Following the lung health of retirees no longer exposed to the factory environment is now the focus of a team of American and Chinese researchers, whose latest grant from the U.S. National Institute for Occupational Safety and Health totals $1.3 million. The team is also probing workers’ DNA for clues to respiratory problems, says study leader David Christiani, professor of occupational medicine and epidemiology at HSPH.
In 1986, China adopted U.S. standards and lowered cotton-dust levels in factories tenfold, from 10 ml per cubic meter to 1 ml, in response to HSPH’s studies linking the dust to lung deterioration and disease. Since then, investigators have turned their attention to dangers posed by potent inflammation-causing biologic agents—endotoxins—which are produced by bacteria that thrive in cotton. During the milling process, these bacteria disintegrate, expelling endotoxins into the air.
Using DNA from long-frozen blood samples, Christiani and colleagues are exploring the relationship among airways disease, airborne endotoxins, and genetic factors—“something we couldn’t even have imagined 25 years ago,” Christiani points out. For example, they’ve found that disease risk appears highest for a small subset of non-smoking workers who have a variant form of a gene called the epoxide hydrolase gene. “We chose to look at this particular variant after a U.K. group uncovered its association with emphysema in smokers,” Christiani explains.
One day, Christiani predicts, doctors might be able to screen
people for this gene variant, then counsel those testing positive to
avoid endotoxins, both at home and on the job. So ubiquitous are endotoxins,
he adds, that they may lurk even in homes, chiefly in humid, mold-prone
By the late 20th century, the cotton textile industry had migrated from Western industrial centers and the American South to Egypt, Mexico, and Asia. As of 1980, China was among the world’s top consumers of cotton, and Shanghai was the center of its textile industry.
Christiani and colleagues recruited 447 factory workers, along with 472 from a silk manufacturing mill to serve as the control group. Every five years, researchers monitored air quality and surveyed participants for acute symptoms, including shortness of breath, chest tightness, and bysinnosis, a variant of asthma.
Many researchers blamed endotoxins for these short-term, reversible symptoms. But as the HSPH team found, they also had lasting ill effects. Says Christiani: “We were the first to show that chronic lung-function loss was related more strongly to prolonged endotoxin exposure than to cumulative dust.”
For Hong-xi Zhang, a physician and professor at Shanghai Second Medical University who joined Christiani’s Shanghai-based team at its inception, the study has special meaning. “Because the study subjects are also my patients, I value the improved work environment,” he says. “Information from our study is very useful in preventing, not just treating, disease. Now, our hospital and district leaders give us a lot more support for prevention-related research.”
In Factories and Homes
Researchers have called for U.S. workplace endotoxin controls for two decades, Christiani says, but the push for health and safety regulations in general has abated under the Bush administration. “No easy, reliable, inexpensive way of measuring endotoxins in air has yet been developed,” Christiani says. When workplace-safety demands resurface, as he believes they will, scientists and legislators will find a wealth of data on endotoxin exposure, and a larger segment of the population in need of protection.
“We started with a very narrow objective, focused on one industry, but our findings now have bearing on the general public,” Christiani says, adding that for him, the ability to introduce effective interventions against disease—whether in China or the U.S., in factories or homes—is “truly rewarding.”
Jack Curtis writes frequently about research and teaching initiatives at Harvard.
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