Deaths From Asthma-COPD Overlap by Industry and Occupation, 1999–2016

Asthma usually involves chronic airway inflammation, airflow limitation that comes and goes, and intermittent symptoms. Chronic obstructive pulmonary disease (COPD) usually involves fixed airflow limitation and persistent symptoms. Some patients show features of both, a condition called asthma-COPD overlap, and they have been reported to fare worse than people with either disease alone. A study by CDC's National Institute for Occupational Safety and Health (NIOSH) looked at deaths from the overlap, and at which industries and occupations they were concentrated in.

How the study worked

The researchers used national multiple-cause-of-death data for 1999–2016, counting decedents aged 25 and older whose death certificates listed both asthma and COPD as an underlying or contributing cause. Death rates were age-adjusted to the 2000 U.S. population. Information on industry and occupation came from 26 states for 1999, 2003, 2004 and 2007–2014, and was used to calculate proportionate mortality ratios (PMRs), which compare the number of overlap deaths in a given industry or occupation with the number expected. A PMR above 1.0 means more deaths than expected.

Deaths and trends

Of U.S. decedents aged 25 and older in 1999–2016, 4,689,828 had COPD and 164,731 had asthma listed as a cause of death. Of these, 18,766 had both — 6,738 men and 12,028 women. The overall death rate was 5.03 per million people (4.30 for men and 5.59 for women).

Rates fell over the period. For men, the annual age-adjusted rate dropped from 6.70 per million in 1999 to 3.01 in 2016, an annual percent change of –4.82%. For women, it dropped from 7.71 to 4.01, an annual percent change of –3.63%.

CDC chart: age-adjusted death rates for asthma-COPD overlap, by sex, 1999–2016.

Working-age adults (25 to 64)

Industry and occupation were known for 784 of 791 decedents in this age group. Significantly elevated PMRs included:

• Not working. Nonpaid workers, nonworkers and people working at home had elevated PMRs among both men (1.72) and women (1.40), as did men (1.98) and women (1.79) who were unemployed, had never worked or were disabled.
• Men in food, beverage and tobacco products industries (2.64).
• Women bartenders (3.28) and homemakers (1.34).

The authors suggest the link with not working may mean the overlap causes enough illness to cost people their jobs, though full work histories were not available to confirm it.

Adults 65 and older

Industry and occupation were known for 1,908 of 1,941 decedents. Elevated PMRs included:

The workplace connection

The American Thoracic Society estimates that about 16% of adult asthma and 14% of adult COPD is due to workplace exposures. Dusts, secondhand smoke, welding fumes and isocyanates can cause both diseases. A 2010 national survey found frequent exposure to vapors, gas, dust or fumes among 52.9% of workers in agriculture, forestry, fishing and hunting, 42.8% in manufacturing, 61.5% of production workers, 50.8% of farming, fishing and forestry workers and 16.5% of people in food preparation and serving. Among nonsmokers in food preparation and serving jobs, 15.4% were frequently exposed to secondhand smoke at work. Cigarette smoking is the main cause of COPD, but 25% of U.S. adults with COPD have never smoked.

Such exposures might explain the higher overlap mortality in certain jobs. The authors point to ways to prevent asthma and COPD at work: eliminating or substituting hazardous exposures, removing workers from them, engineering controls such as ventilation or enclosing processes that create exposures, and smoke-free workplace policies, along with continued surveillance.

Limitations

• There is no specific diagnosis code for asthma-COPD overlap, and diagnoses could not be verified; lung disease may be underreported on death certificates.
• There are no codes for occupational asthma or COPD, so it could not be shown that workplace exposures caused the illnesses.
• Death certificates record a person's usual occupation and industry, which may not be where exposure occurred, especially for people who changed jobs or held more than one.

Sources

• Katelynn E. Dodd, John Wood and Jacek M. Mazurek, "Mortality Among Persons with Both Asthma and Chronic Obstructive Pulmonary Disease Aged ≥25 Years, by Industry and Occupation — United States, 1999–2016," Morbidity and Mortality Weekly Report, CDC: https://www.cdc.gov/mmwr/volumes/69/wr/mm6922a3.htm