In many cases, asthma that first strikes in adulthood may be caused by exposure to substances in the workplace, according to researchers.
Asthma linked to on-the-job exposures is a well-known phenomenon, but the latest findings suggest it "may be more common than is realized," reported Dr. Anthony Johnson of the University of Sydney in Australia and colleagues in Canada.
Bacteria and molds, as well as chemicals, fumes and gases have all been found to trigger asthma in workplaces.
Examples of occupational asthma include farmers and grain-storage workers whose asthma results from exposure to grain mites.
Henna has caused asthma in hairdressers; flour in bakers; penicillin in pharmacists; cobalt dust in metal grinders; oil mists in tool setters; and cedar dust in carpenters and sawmill workers.
Johnson''s team conducted a survey of nearly 19,000 randomly selected Canadian adults aged 20 to 44.
Of these, about 3,000 underwent laboratory tests and completed supplementary questionnaires.
They published their findings in the December 2000 issue of the American Journal of Respiratory and Critical Care Medicine.
In total, 383 people in the study were found to have asthma, 166 of whom had their first attack as an adult.
In these "adult-onset" asthmatics, more than one in three were deemed to have "possible" or "probable" asthma linked to their place of work.
The investigators based their estimate on the numbers of asthmatic study participants employed in environments where they might be exposed to various substances linked with asthma.
In the majority of cases, the suspected causes of asthma were latex, flour, grain and vegetable gum, Johnson''s team said.
Nursing, clerical jobs and food preparation occupations were most commonly linked to asthma.
Other researchers have shown that occupational asthma strikes millions of people worldwide, causing disabling illness and a high rate of unemployment.
Based on their results, Johnson and colleagues estimate that reducing exposure to substances known to trigger asthma attacks could prevent almost one in five cases of adult-onset asthma.
by Virginia Sutcliffe