Autoimmune Mortality Higher Among Some Benign Professions

SEATTLE, Sept. 28 -- There is something about farming, nursing, and teaching that seems to predispose those who work at these professions to death from systemic autoimmune diseases, reported investigators here.

Other occupations consistently associated with death from autoimmune disease included textile machine operation, mining machine operators, painting and decorating, reported Laura S. Gold, M.S.P.H., of the Fred Hutchison Cancer Center, and colleagues, in the October issue of Arthritis & Rheumatism.

These findings emerged from a case-control review of U.S. death certificates from 26 states from 1984 to 1998, with the authors flagging any cases that listed a systemic autoimmune disease such as rheumatoid arthritis, systemic lupus erythematosus, or systemic sclerosis as a cause.

The study suggested that occupations involving exposure to chemicals or animals, or both, might put workers at increased risk for autoimmune conditions, as may some -- but not all -- careers involving public exposure.

For example, nursing and teaching were associated with increased risk, but food preparation and handling was associated with a lower than average risk of mortality from autoimmune conditions.

The investigators also included in their analyses disorders with suspected but not proven autoimmune origin, such as unspecified connective tissue disorders.

For each case five controls matched by age, gender, race, year of death and geographic region were also selected.

The investigators determined the longest-held occupation of each case using the "usual occupation" box from death certificates. They also looked at specific occupational exposures such as pesticides and fertilizers in farming, and the use of benzene and solvents in manufacturing. Jobs involving significant exposure to other people, such as nursing, teaching, and restaurant work, were also examined.

They identified 36,178 deaths attributed to RA, 7,241 to lupus, 5,642 to systemic sclerosis, and 4,270 to other autoimmune disease.

The researchers found that "a broad array of occupations was associated with death from systemic autoimmune diseases, including several of a priori interest," they wrote.

The odds ratio for death from systemic autoimmune disease among farmers was 1.3 (95% confidence interval 1.2 to 1.4). When they looked at specific diseases, only RA was significantly associated with death among farmers, particularly for farmers who worked with crops rather than with livestock.

Industrial occupations significantly associated with autoimmune disease mortality included mining machine operation (odds ratio 1.3, 95% CI 1.1 to 1.5), miscellaneous textile machine operators (odds ratio 1.2, 95% CI 1.0 to 1.4), and hand painting, coating, and decorating (odds ratio 1.8, 95% CI 1.0 to 2.9).

Certain public exposure occupations were also associated with increased risk of death from autoimmune conditions. For example, elementary school teaching was associated with an odds ratio for death from any autoimmune disease of 1.23 (95% CI, 1.16 to 1.30), special education teaching was associated with and odds ratio of 1.92 (95% CI 1.10 to 3.17), and nursing was associated with an odds ratio of 1.09 (1.01 to 1.17).

"These occupations were also significantly associated with death from the specific autoimmune diseases examined," the authors noted. For example, occupational exposure to the public was associated slightly with death from lupus (odds ratio 1.1, 95% CI 1.0-1.2), and exposure to animals was associated with a 28% increase in risk of death from rheumatoid arthritis.

But other public exposure jobs were associated with decreased risk for death from autoimmune diseases, including butchers, waiters/waitresses, and cooks (except short-order cooks), the authors noted.

In an analysis by age, they found that the higher-risk occupations and exposures were also present among those people who were past typical retirement age at the time of death, "implying that the occupational exposures were involved in a chronic pathogenic process leading to either disease incidence or slow progression of existing autoimmunity," they wrote.

They suggested that the association between nursing, teaching, and other jobs with high public exposure may be related to exposure to multiple infectious agents that could trigger autoimmunity. In addition, because teachers and nurses tend to have good health insurance coverage, deaths from autoimmune diseases may be more frequently captured in vital records than deaths among others with public exposure but less reliable health coverage, such as waiters and waitresses, they suggested.

"The size of our study allowed us to estimate associations between specific occupations and death from autoimmune diseases and to generate hypotheses that will be useful as starting points for future studies in this area," the authors concluded.

Their study was limited by a tendency to underreport autoimmune disorders on death certificates, and by potential biases associated with the availability of health insurance.