Mesothelioma incidence describes the number of new cases diagnosed in a population over some range of time. Researching the incidence of asbestos cancer for specific groups of people is a major aspect of epidemiology, which can provide valuable information about patterns of the disease.
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Epidemiology is the study of a disease's origin and defining characteristics. With data collected from epidemiological studies, researchers can identify the populations at highest risk for cancer. Whereas the prevalence of the disease only measures the total number of cases observed at any given time, the disease's incidence also reveals a group's overall risk for the disease, which is an important detail for researchers to consider.
Another key element of the epidemiology of a disease is its etiology — or causes. Cancer researchers study the characteristics of patients who have been diagnosed with the asbestos-related illness to establish what factors may cause the cancer.
By studying changes in the incidence rate and other trends over time, scientists can devise better measures for preventing asbestos diseases among high-risk groups.
Source: National Cancer Institute, SEER Cancer Incidence Rates.
Incidence rate is typically expressed as the number of potential cases per 100,000 people, but can also be expressed in cases per million. According to 1975 to 2010 records from the National Cancer Institute, the average asbestos cancer rate in the United States was 1.0 new cases per 100,000.
The incidence rate for Americans in general peaked in 1994 and 1995 at 1.16 per 100,000. The peak rate among men during this period was even higher, hitting 2.49 per 100,000 in 1992. In comparison, the peak rate for women occurred in 1983 at 0.49 per 100,000.
Mesothelioma incidence is also influenced by ethnicity. At 0.55 new cases per 100,000, the rate for black Americans from 1975 to 2010 was much lower than the rate of 1.09 per 100,000 for whites.
|Sex||Age||Diagnosed from 2004-2005||Diagnosed from 2006-2007||Diagnosed from 2008-2010|
Source: National Cancer Institute, SEER Cancer Incidence Rates.
Aside from factors like age, race and gender, epidemiologists may also examine incidence rates for specific industries and geographical regions. This data can help them determine the locations and occupations associated with the highest risk for developing a form of the disease.
The cause of asbestos cancer is primarily attributable to asbestos exposure, and the majority of patients were first exposed to the toxic mineral while on the job. Higher rates of mesothelioma are associated with certain industries that made extensive use of asbestos materials.
Research indicates that some of the highest rates occur among shipyard workers, especially those who served the industry during World War II. Other occupations associated with high mesothelioma rates include U.S. Navy veterans, various tradesmen in the construction industry, pipefitters and welders, boiler workers, maintenance workers, machinists and electricians.
According to the U.S. Centers for Disease Control and Prevention (CDC), the industries with the greatest number of mesothelioma deaths in 1999 included:
The occupations with the most mesothelioma deaths that year included:
The Health and Safety Executive, a workplace health organization in the United Kingdom, has more recent data on occupations at high risk for mesothelioma. From 2002 to 2010, the following occupations had the highest number of mesothelioma deaths for men in the U.K.:
One notable epidemiological study from the 1970s revealed excessively high rates of asbestos disease in Tidewater, Virginia. It soon became apparent that the high rate occurred primarily among male shipyard workers.
Several large shipyards in coastal Virginia were active during World War II, and some continue to employ a large number of workers today. Researchers reviewed mesothelioma data collected from 1972 to 1978, and the annual age-adjusted incidence rate was determined to be 2.7 per 100,000 among white males who worked in the industry. This figure is four times higher than the national average of 0.7 per 100,000, indicating that Tidewater shipyard workers are part of a high risk group.
Most of the men involved in the study began working for the industry prior to 1950, and the average latency period for these cases was 34 years. Furthermore, the rate was highest in the 60- to 69-year-old age group, at 14.1 per 100,000. Information gained from epidemiological studies like this is invaluable, as it can be used to improve working conditions and health care procedures for high-risk groups.
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The U.S. holds the largest number of mesothelioma cases and asbestos tonnage per year. While statistics are outdated, they offer a correlation between diagnoses and amount of asbestos mined in North America, Europe and Australia.
International Regions with High Rates of Mesothelioma
|Country||Cases per year||Asbestos tons per year|
|United States||2,800 (2000)||552,000 (1975)|
|Great Britain||1,595 (1999)||170,000 (1970)|
|Germany||1,007 (1997)||230,000 (1975)|
|Italy||930 (1995)||140,000 (1975)|
|France||750 (1996)||143,000 (1970)|
|Australia||490 (2000)||70,000 (1970)|
Because of the close relationship between asbestos exposure and mesothelioma incidence, geographical areas with naturally occurring deposits of the mineral have exhibited historically high rates of mesothelioma. Areas containing former asbestos mines are considered major mesothelioma hot spots.
Regions in the U.S. with High Rates of Mesothelioma
Researchers have also observed high rates of mesothelioma in regions and communities that relied heavily on asbestos, including places with a history of shipbuilding and industry. One example is the borough of Manville, New Jersey.
From 1912 to 1980, Johns Manville Corporation operated a large asbestos manufacturing plant in Manville. Epidemiologists studied the impact of asbestos production on the borough's residents because many of them worked at the plant, where they were occupationally exposed to airborne fibers.
The mesothelioma rates in the Manville plant were roughly 25 times higher than the average statewide rates. For males, the rate was 10.1 per 100,000, and for females it was 22.4 per 100,000.
|State/Region||Incidence per 100,000|
California is home to some of the largest deposits of naturally occurring asbestos in the world, and according to the Environmental Working Group, the state ranks No. 1 for asbestos-related deaths in the United States. Because the average life expectancy for mesothelioma patients is only about a year, the disease's mortality and incidence rates are typically very close. The age-standardized incidence rate for California in 2005 was 12.6 new cases per million, compared with the national rate of 14.0 per million.
Researchers predict that New York City is also destined to become a hot spot. Because of the large clouds of asbestos dust released by the collapse of the Twin Towers, it is believed that mesothelioma could become a huge concern for New York City paramedics, police, firefighters or anyone else who lived in Lower Manhattan immediately after the tragedy.
Fast Fact: One of the most prominent hot spots is Libby, Montana. This city was home to an asbestos-tainted vermiculite mine that was owned and operated by W.R. Grace and Co. for more than 40 years.
Trends in mesothelioma incidence reflect the changes that occur over a defined period of time. Studying these trends is quite possibly the best method for determining mesothelioma’s burden on a specific population.
In the United States, the peak incidence of mesothelioma took place in the early to mid-1990s after a sharp increase starting in the early 1970s. Since then, however, mesothelioma rates have started to decline.
In 1994 to 1995, the rate peaked at 1.16 per 100,000. From 1996 to 2010, the rate fluctuated, but showed a declining trend. The average incidence rate for the 15-year period was 1.03 per 100,000, which suggests the rate is falling in America and fewer people are developing the disease.
But in Australia and some European countries, the incidence of mesothelioma may still be rising. This can most likely be explained by these countries’ lengthier and more extensive use of amphibole asbestos, which is considered more toxic than the chrysotile type used predominantly in the United States.
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