November 12, 2001

Health Center researcher Stephen Walsh connected the dots in a way that has made U.S. public health authorities and government officials think differently about autoimmune diseases: he found evidence that some school teachers are in danger from their students - not from violence, as you might imagine - but from illness.

Walsh, an assistant professor in the Department of Community Medicine and Health Care, published work last summer in the Journal of Rheumatology that found schoolteachers, overall, were 10 to 15 percent more likely to die from an autoimmune disease than people in other professions. When he analyzed deaths by age, he found that schoolteachers in the 35- to 44-year-old group died 50 percent more often from autoimmune diseases.

"We expected to find some evidence of excess mortality in school teachers," he says. "I never anticipated that we would see a pattern relative to age that would fit as beautifully as it does with the dominant theory of how these diseases develop."

Autoimmune diseases are a class of at least 20 and as many as 60 different illnesses that affect the immune system. They include rheumatoid arthritis, lupus, multiple sclerosis, scleroderma and juvenile diabetes, illnesses that are caused by a person's own immune system attacking some part of the body - for example, the heart, kidneys, joints, or skin. Over time, the immune system permanently damages and disables the structure under attack, leading to chronic disease and, often, to death.

Three years ago, while Walsh was examining national death statistics grouped by occupation, he decided to look up causes of death among teachers. In an earlier study, he had found evidence in teachers of excess mortality from scleroderma, an autoimmune disease. The national data didn't specifically identify autoimmune diseases, but the broader disease groups that included them consistently showed higher mortality among teachers.

Walsh hypothesized that if deaths from autoimmune diseases could be isolated, he might confirm that teachers broadly experience higher mortality from this group of related diseases.

With a grant of $25,000 from the Health Center Research Advisory Committee to fund his research, he and research assistant Laurie DeChello began to gather and analyze data from more than 6 million death certificates.

For individuals with aggressive cases of autoimmune disease, deaths generally begin to occur between the ages of 35 and 45. That's because the diseases normally manifest themselves about age 25 and, for serious cases, run their course in 10 to 15 years.

The data supported that: there were few deaths and no evidence of excess mortality in schoolteachers between ages 25 and 35. In the 35-44 age group, however, there were not only many more deaths, but the deaths were occurring at a much higher rate than in other occupations. The excesses continued, but steadily declined with age.

The pattern of mortality across age groups conformed to a standard epidemiological phenomenon known as "depletion of susceptible individuals over time" - or in other words, those who are likely to get a disease do so and suffer its effects, such as death. As time passes, fewer susceptible individuals remain and the number of new cases and deaths begin to decrease.

"What seems to be happening is that teachers who are susceptible to auto-immune diseases start their careers and, very shortly afterwards, encounter one or more triggers, perhaps in the school setting, that initiate an autoimmune disease," he says. "For some of these individuals it leads to death."

What could that trigger be?

Scientists know that rheumatic fever, also an autoimmune disease, is triggered by streptococcal bacteria - the bacteria that cause strep throat. Rheumatic fever was one of the diseases that teachers in the 35-44 year age group were dying from more often than expected. This led Walsh to think that the other autoimmune diseases among teachers might also be triggered by infectious agents.

Four other autoimmune diseases were significantly more common among teachers - lupus, rheumatoid arthritis, Sjogren's disease, and multiple sclerosis. For each of these diseases there's evidence to suggest that Epstein-Barr virus is the environmental trigger. Epstein-Barr is the cause of infectious mononucleosis, a disease common among American high school students. Coincidentally, Walsh's findings showed that high school teachers were significantly more likely to die from an autoimmune disease than elementary school teachers.

Walsh says more work is needed, but a couple of points have emerged:

"The investigation constitutes one of the first epidemiological studies of autoimmune diseases as a unified group of related diseases. In looking at them, we see evidence that's consistent with the possibility that infectious diseases provide an environmental trigger for the most common autoimmune diseases.

"Secondly, in schoolteachers, we have identified a readily available population in which to study the development of autoimmune diseases. By using this group, we may successfully identify the environmental factors - infectious agents or not - that increase risk of disease and cause the excess mortality among them."

Walsh has received a grant from the National Institute of Allergy & Infectious Diseases to pursue this work further.

Pat Keefe