Do Occupational Exposures Increase the Risk of Death from Systemic Autoimmune Disease

Arthritis News > Occupational Exposures adn Systemic Autoimmune Disease

Do Occupational Exposures Increase the Risk of Death from Systemic Autoimmune Disease?

Jon Giles, M.D.

Background:

Both genetic and environmental exposures, to varying degrees, are felt to contribute to the risk and severity of systemic autoimmune diseases (e.g. rheumatoid arthritis (RA), lupus, etc…).  While some clear cut evidence for environmental exposures in certain autoimmune diseases exists, such as cigarette smoking in RA and specific chemical exposures in scleroderma-like syndromes, general links to occupational exposures has been difficult to establish.  This is partially due to difficulties in tracking and quantifying specific exposures within complex frameworks, particularly when exposure likely precedes onset of disease by years or even decades.  Here, Gold et al (Arthritis Rheum 2007; 56:3189) explore the association of occupation and risk of mortality from a variety of systemic autoimmune diseases.

Methods:

Death certificate data from 26 U.S. states were used.  Cases were selected using ICD.9 codes for a variety of systemic autoimmune diseases (RA, SLE, scleroderma, Sjogren’s, dermatomyositis, polymyositis, and unspecified connective tissue disease and polyarthropathy) from those reported on the death certificates.  Five controls without explicit autoimmune disease were frequency matched to the cases based on age, gender, race, year of death, and geographic location.  “Usual occupation” was obtained from the death certificate.  Only subjects age 25 and over were included to allow at least 5 years of potential occupational exposure prior to death.

Results:

There were 52,277 deaths in which autoimmune diseases were listed on the death certificate compared to 260,632 controls without a listed autoimmune disease.  Among these were 35,730 cases of RA, 7,153 cases of SLE, and 5,578 cases of scleroderma.  Autoimmune disease was listed as the primary cause of death in one third of cases with autoimmune disease.

Among occupational categories, those significantly associated with mortality from autoimmune disease, in general, included teachers, secretaries, bank tellers, bookkeepers, farmers, mining machine operators, dressmakers and textile machine operators, and those in the handpainting and coating occupations.  For specific diseases, farmers, teachers, timber cutters, separating and filtering machine operators, and mining operators were at the highest risk for RA mortality.  Elementary school teachers and teacher’s aids, barbers, handpainters, and textile machine operators were at greatest risk for SLE mortality.  Firefighters, typesetters, and in particular, handpainters and coaters were at the greatest risk for scleroderma mortality.
Among specific exposures estimated from occupations, exposures to animals and pesticides were the most highly associated with RA mortality, exposures to the public with SLE mortality, and exposures to asbestos and nitrogen oxides with scleroderma mortality.

Conclusions:

Specific occupational exposures are associated with an increase in mortality from certain autoimmune diseases.

Editorial Comment:

These are interesting findings that support some long-held (but difficult to systematically evaluate) notions about environmental exposure and autoimmune disease; that RA is more highly associated with exposures to inhaled particulates, SLE with frequent infections (such as a teacher would encounter), and scleroderma with exposure to chemicals and solvents.  Although interesting, this study cannot prove causality or demonstrate whether the observed link is related to the assumed occupational exposure or a factor linked to the occupation that is not being measured directly.  In addition, this type of epidemiologic study benefits from the large number of subjects involved, but suffers due to potential lack of accuracy in the measure of exposures and outcomes.  For example, death certificate data are not standardized, and chronic conditions, like most autoimmune diseases, tend to not show up on death certificates.  When they do, it is usually because disease was particularly severe.  While this is good for specificity, there is a risk of diluting associations as patients with milder autoimmune conditions will be included among the “non-exposed” comparison group.  Regardless, these findings are helpful in focusing research into certain areas of exposure that can be further explored.

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