Prevalence

Prevalence is the share of a group of people who have a disease or condition at a particular time, counting both new and long-standing cases. It is usually given as a percentage. In asbestos studies it often describes how common pleural plaques or asbestosis are among workers in a trade.

Origin

Prevalence is a basic measure of epidemiology. Cross-sectional surveys that X-rayed whole workforces, common in occupational medicine from the 1930s onward, reported their results as prevalence, and many classic studies of asbestos workers did the same.

Significance in Asbestos Context

Prevalence studies helped show how widespread asbestos disease was among workers. When researchers X-rayed insulators, shipyard workers or miners, they reported the prevalence of plaques and scarring, and found that it climbed steeply with years since first exposure. Those figures are still cited in expert reports and in the history of what was known about asbestos hazards. Prevalence differs from incidence: a long-lasting condition like pleural plaques builds up a high prevalence even if few new cases appear each year, while a rapidly fatal cancer has a low prevalence even when new cases are common. Prevalence surveys also have a weakness: workers who became sick and left the job, or died, are missing from the count, so the true burden can be understated. For a family, prevalence figures help explain why a doctor looks for plaques in someone with decades-old exposure, but they describe groups, not one person's diagnosis.

Example Sentence

A survey of retired insulators found a prevalence of pleural plaques of more than 50 percent among men first exposed more than 30 years earlier.

Related Terms

Incidence, Epidemiology, Pleural Calcification Prevalence, Pleural Plaques, Healthy Worker Effect, Selikoff Studies, Latency

Notes

• A high prevalence of plaques in your trade is a reason to ask your doctor for a chest X-ray or CT, not a diagnosis.
• Check whether a study counted all workers or only those still employed; it affects how the figure should be read.