While most people are exposed to small amounts of naturally occurring asbestos deposits in the air, deposits in the earth, and thus, drinking water and the deterioration or aging of asbestos-based products and materials, the onset of complications from exposure to asbestos fibers usually occurs with exposure at much higher concentrations.  Exposure to asbestos is the primary risk factor for mesothelioma. Prior to 1989, exposure at the workplace, schools and homes was prevalent. Since that time government regulations have limited the construction of asbestos-based materials and set standards for exposure levels in places where exposure is still a risk. The largest population of mesothelioma patients in the US is white males who were disproportionately employed (as compared to females and people of other races) in industries where the risk was greatest.    A study of mortality for mesothelioma by the National Institute for Occupational Safety and Health (NIOSH) indicates that more than 7,500 individuals died from mesothelioma in the US from 1999 through 2001. The study examined the geographical and occupational distribution of mesothelioma. This study is of significance since it provides a better estimate of mortality rates than was achievable in earlier studies. Through evolving research and development in the area of mesothelioma, the medical profession is better skilled at diagnosing asbestos and accounting for effects of the disease. Historically, mesothelioma has been misdiagnosed as a form of cancer since symptoms of the disease are also characteristic of other illnesses and diseases. In many cancer studies, incidences of mesothelioma were underrepresented or not accounted for because incidences of mesothelioma were included in the data for other types of cancer rather than being compiled as a separate form of cancer.  The NIOSH study predicts mortality rates using age-adjusted estimates of death. The study also provides statistics based on a proportionate morality ratio (PMR), which is calculated as number of deaths from mesothelioma per the expected number of deaths from mesothelioma. The study indicates that the highest PMR of mesothelioma in industry were found to be in the shipbuilding and ship repairing industries. This rate is consistent with results from other studies and it is consistent with the high rate of exposure to asbestos in those industries. The second highest PMR was found to be in the industrial chemical industry. The third highest PMR was in the construction industry.  The NIOSH study accounts for deceased construction workers from 19 states where there was asbestos exposure to building materials. The following table shows the number of deaths and PMR for industry. The data represents US residents age 15 and over in the 19 states. 

 The NIOSH study also indicates that the highest rates of death, as ranked by occupation (job title), were plumbers, pipefitters, steamfitters, mechanical engineers and electricians as indicated in the following table. 

  The study estimates 85% of mesothelioma deaths to be males. This is consistent with the history of workplace compositions. Men had more exposure to asbestos since few females worked in the construction and shipbuilding industries prior to 1960 when exposure was highest. Inline with other studies, female morality rates were highest for those females exposed to male workers who brought asbestos home from the workplace and those females in teaching positions. High rates of death were reported for schoolteachers, some of which were female. The highest incidence of exposure is suspected for schools built between 1945 and 1773. The following table shows demographic characteristics of mortality rates for mesothelioma as indicated by the NIOSH study. The table shows the type of mesothelioma by median age, sex and race. It is possible for patients with mesothelioma to die from symptoms and effects of the disease rather than the disease itself. As such, the following table shows the percentage of deaths where the underlying cause was malignant mesothelioma. 

 Elevated mortality rates were reported for residents in the coastal communities of California, Florida, Pennsylvania, New York, Illinois, Texas, Ohio, New Jersey, Michigan and Massachusetts. The highest rates were reported for Somerset County, New Jersey, where asbestos products were manufactured.