NEW YORK (Reuters) - Not everyone exposed to high noise levels at work experiences hearing loss as a result, and a new study suggests a simple test can predict which workers will be affected.
Researchers caution that low accuracy in predicting who would not suffer hearing loss means the test shouldn’t be used to select employees to work under high noise conditions.
Nor should the test be used “to exclude workers from occupational noise exposure, but for improving counseling especially concerning use of hearing protectors and for a tighter schedule for hearing tests,” said one of the study authors, Dr. Michael Kundi, at the Institute of Environmental Health in Vienna, Austria.
In the study, the test did do a better job of predicting which workers would experience hearing loss than traditional risk factors like how long workers were exposed to noise and how often they wore hearing protection.
Approximately 15 percent of Americans between the ages of 20 and 69 have hearing loss that is possibly caused by noise at work or during leisure activities, according to the National Institute on Deafness and Other Communication Disorders.
According to the U.S. Occupational Safety and Health Administration (OSHA), 30 million Americans are exposed to hazardous noise levels at work.
Researchers have long sought to understand differences in hearing loss experienced by people exposed to similar noise levels in the workplace. Studies at the authors’ institute have found that variations in the inner ear’s reaction to noise are partly responsible, meaning some people are more susceptible to hearing loss than others, likely due to genetics.
One indicator of a person’s susceptibility is how quickly the cells of the inner ear recover from noise exposure, which can be detected by measuring so-called temporary threshold shift (TTS) – a temporary hearing loss that’s also known as aural fatigue or auditory fatigue.
The TTS test exposes participants to frequencies between 200 and 500 Hertz at about 100 decibels. After the exposure, the researchers perform an audiogram at 4 kilohertz for at least 10 minutes.
The magnitude of TTS after 2.5 minutes may indicate whether the person is more likely to suffer permanent noise-induced hearing loss, according to the authors.
For their study, published in Occupational and Environmental Medicine, they followed 125 white, male teenage apprentices working as fitters and welders at a steel company in Austria.
They measured the participants’ hearing at the start of the apprenticeship in the morning hours, before workers were exposed to workplace noise. The study followed the apprentices, conducting hearing tests every three to five years for an average of 13 years.
The study team found that 82 percent of the workers considered vulnerable to hearing loss based on the initial test did lose hearing over the years.
When predicting who was not likely to experience hearing loss, however, the test was correct only 53 percent of the time.
OSHA requires employers to implement a “hearing conservation program” when workers are exposed to noise of 85 decibels or more over an eight-hour shift. The rule requires “employers to measure noise levels, provide free annual hearing exams and free hearing protection, provide training, and conduct evaluations of the adequacy of the hearing protectors in use” (see: 1.usa.gov/1vnyj2o).
The current study suggests that such restrictions may be more effective for some workers than others, Kundi notes. Although he doesn’t recommend the test be used to assign workers to noisy jobs or exclude them, the TTS test could identify people who are particularly vulnerable.
The test is not expensive, he said, and can be done during regular occupational hearing tests. A person concerned about hearing loss could also get this test on his or her own. An ear, nose and throat specialist with an audiometer and a noise generator can perform it, Kundi said.
“It would be premature to recommend this screening method for general use until these findings have been replicated by an independent group,” said Dr. Robert Dobie, an ear specialist at the University of Texas Health Science Center in San Antonio. “Even then, its apparently poor performance (especially its low specificity) would dampen enthusiasm,” Dobie told Reuters Health by email.
Dobie, who was not involved in the study, also worries that “it might lead to inadequate prevention and counseling efforts for people who appeared - by this test - to be resistant to noise damage,” he said. “At this point in time, it seems best to treat everyone as susceptible.”
For workers concerned about noise exposure, Dr. Hanns Moshammer, who led the Austrian study, said it’s important to let the inner ear recover by reducing noise in activities outside of work.
After a person has been exposed to loud noise, “for recovery, the cells need calm conditions for the rest of the day,” he said. Increasingly, “recreational noise, games and loud music threaten our hearing faculty,” he added, and advised that people exposed to noise at work avoid noisy leisure activities.
Hans-Peter Hutter, senior author of the study, added in an email that “noise induced hearing loss (NIHL) represents a public health challenge as numbers are increasing – we think that our findings are a further step in the prevention of this health problem.“
SOURCE: bit.ly/1tlA284 Occupational & Environmental Medicine online July 25, 2014.