The NIOSH Review of Hand-Arm Vibration Syndrome: Vigilance Is Crucial


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There is strong epidemiologic evidence that high-level exposure to vibration is associated with the vascular symptoms of hand-arm vibration syndrome (HAVS), our conclusion in Musculoskeletal Disorders and Workplace Factors.1 The epidemiologic literature consistently shows that one critical factor for development of HAVS is "vibration dose," which is a product of vibration level and exposure time. Also consistently seen is a strong relationship between exposure time and the severity of HAVS. The literature clearly shows that the use of antivibration devices on tools, particularly those on chain saws, have extended the time interval between exposure to vibration and development of symptoms (the latent interval). Hadler2 admits that much has been accomplished in high-exposure occupational groups (such as quarrymen and chain-sawyers) to modify and design new tools, and to control exposure through administrative action, personal protection, and through medical monitoring to reduce the occurrence of HAVS, all of which are the crux of the recommendations found in the NIOSH Criteria for a Recommended Standard on Occupational Exposure to Hand-Arm Vibration.3 The epidemiologic and clinical data support the conclusion that healthy workers who use vibrating tools can be protected from developing the disabling effects of HAVS.Although advanced stages of HAVS are extremely rare these days, it is estimated that hand-arm vibration jeopardizes the health and future employability of two million workers in the United States and the United Kingdom alone.4 An estimated 8% of currently employed US workers report exposure to vibrating hand tools over four hours in a workday.5 Behrens and Pelmear6 found high usage in the construction, ship-building, agriculture and forestry, and mechanical engineering industries. Behrens et al7 noted that the prevalence of HAVS was greater among incentive workers than among workers paid by the hour in the United States. Vibration exposure continues to be a significant hazard in many contemporary work environments.In his editorial, Dr. Hadler expressed concerns about the epidemiologic evidence that was used to support the conclusions of the National Institute of Occupational Safety and Health regarding the work-relatedness of HAVS. In this response, we will examine relevant information from the NIOSH epidemiologic reviews and discuss the issues raised by Dr. Hadler.The 1997 NIOSH Musculoskeletal ReviewIn 1997, NIOSH published a critical review of the epidemiologic literature of selected musculoskeletal disorders (MSDs) of the upper extremity (including HAVS) and low back and their relationships to physical factors at work.1 Greater focus was given to studies that had objective exposure assessment, high participation rates, a physical examination as part of the epidemiologic case definition, and a blinded assessment of either health or exposure status. Further analysis determined whether studies were likely to be substantially influenced by confounding or other epidemiologic limitations that might have major influences on the interpretation of findings. These included the absence of non-respondent bias, selection bias, and comparability of study and referent groups. The document also described information about confounders and epidemiologic pitfalls for each detailed study reviewed. After assessing the quality of individual epidemiologic studies, NIOSH investigators judged whether the evidence was strong enough to relate the exposure factor to the MSD. The framework for evaluating evidence for causality in the review included a modified Bradford-Hill8 characterization of each study, looking at strength of association, consistency, temporality, exposure-response relationship, and coherence of evidence.In his editorial, Dr. Hadler suggests that the HAVS chapter is limited in that it presents a review of only recent literature. It should be pointed out that in preparation of the document, HAVS presented NIOSH researchers with a charge different from that of other disorders.

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