obÌåÓý

Abstract

Idiopathic pulmonary fibrosis (IPF), a progressive lung disease characterized by scarring and worsening lung function, has a poor prognosis. A recent systematic review estimated that 21% of IPF deaths might be attributable to occupational exposures. To describe IPF mortality among U.S. residents aged ≥15 years who were ever employed, by industry and occupation, obÌåÓý conducted an exploratory analysis of 2020–2022 multiple cause-of-death data. During 2020–2022, a total of 67,843 (39,712 [59%] male and 28,131 [41%] female) decedents had IPF, suggesting that during this 3-year period, 8,340 IPF deaths in males and 5,908 deaths in females might have been associated with occupational exposures. By industry group, the highest proportionate mortality ratios among males were among those employed in utilities (1.15) and among females, were among those employed in public administration (1.12). By occupation group, the highest IPF mortality rates among males were among community and social services workers (1.23) and among females among farming, fishing, and forestry workers (1.24). Estimates of elevated IPF mortality among workers in specific industries and occupations warrant confirmation, control of known exposure-related risk factors, and continued surveillance to better understand the full range of occupational exposures that might increase risk for developing IPF.

Introduction

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive scarring of lung tissue and declining lung function, with a median survival of 3–5 years after diagnosis (1). Typically, the disease presents with unexplained, progressive shortness of breath, often accompanied by a nonproductive cough and a radiographic pattern of usual interstitial pneumonia on high-resolution computed tomography (1,2). Treatment options are noncurative and include pharmacotherapies (i.e., pirfenidone and nintedanib to slow progression) and lung transplantation (1,2).

In 2017, the overall IPF age-adjusted death rate (IPF deaths per 100,000 persons) was 5.4 (7.2 for men and 4.0 for women) (3). Although the exact IPF etiology remains unknown, studies have indicated associations with cigarette smoking, genetic mutations, viral infections (e.g., Epstein-Barr virus and hepatitis C), and occupational exposures to pesticides, and wood (pine) and metal (brass, lead, and steel) dust (1,2,4,5). The proportion of IPF cases associated with occupational exposures (the population attributable fraction) has been previously estimated to be 21% (95% CI = 15%–28%)* (6). To describe IPF mortality among U.S. residents aged ≥15 years by industry and occupation and to examine associations among IPF deaths and industry and occupation, obÌåÓý analyzed 2020–2022 multiple cause-of-death data.

Methods

Data Source

Deaths were identified from the National Vital Statistics System’s (NVSS) public-use multiple cause-of-death files,^† which include 10,038,112 records for U.S. residents aged ≥15 years who died during 2020–2022, the most recent years the jurisdictions^§ provided information on decedents’ usual^¶ industry and occupation. The NVSS mortality files include coded industry (23 major groups) and occupation (26 major groups) information for 9,738,271 decedents.**

Case Definition

IPF decedents were defined as persons whose death record listed the International Classification of Diseases, Tenth Revision (ICD-10) code J84.1 (other interstitial pulmonary diseases with fibrosis) as the underlying^†† or a contributing cause of death. Following previous reports (3), death records listing ICD-10 codes for conditions that might be associated with nonidiopathic pulmonary fibrosis^§§ were excluded from the analysis (3,033 [4.3%] of 70,876 death certificates listing ICD-10 code J84.1).

Data Analyses

Death rates (deaths per 100,000 persons aged ≥15 years) were based on postcensal population estimates as of July 1 of the corresponding year and were age-adjusted using the 2000 U.S. Census Bureau standard population.^¶¶ Because some occupations are dominated by either male (e.g., mechanics, carpenters, and electricians) or female (e.g., preschool and kindergarten teachers, childcare workers, and administrative assistants) workers,*** and because the IPF-related mortality is higher in males than in females (3), proportionate mortality ratios (PMRs),^††† adjusted by 10-year age groups, race and ethnicity, and 95% CIs assuming Poisson distribution of the data were calculated by industry and occupation for males and females. One occupation might be listed under multiple industries. Analyses were conducted using SAS software (version 9.4; SAS Institute). This activity was reviewed by obÌåÓý, deemed not research, and was conducted consistent with applicable federal law and obÌåÓý policy.^§§§

Results

IPF Deaths and Death Rates

During 2020–2022, a total of 67,843 deaths with IPF listed as the underlying (38,869; 57.3%) or a contributing (28,974; 42.7%) cause of death among U.S. residents aged ≥15 years were reported (Table 1), accounting for 0.7% of 9,738,271 deaths from all causes. Among IPF deaths, 45,646 (67.3%) occurred among persons aged ≥75 years, 39,712 (58.5%) occurred among males, 61,356 (90.4%) among White persons, and 60,793 (89.6%) among non-Hispanic persons. Overall, the annualized age-adjusted IPF death rate was 7.1 per 100,000 persons. The highest IPF death rates were among adults aged ≥75 years (67.6 per 100,00 persons), males (7.7), non-Hispanic (7.7), and White persons (8.2). Based on an estimate that 21% of IPF deaths might be related to occupational exposures, during this 3-year period, 8,340 (95% CI = 5,957–11,119) IPF deaths in males and 5,908 (95% CI = 4,220–7,877) deaths in females might have resulted from occupational exposures.

Industry

By industry, the highest number of IPF deaths occurred among males in the manufacturing industry (7,525; 18.9% of IPF deaths in males) and among females in the health care and social assistance industry (4,277; 15.2% of IPF death in females) (Table 2). The highest significantly elevated PMRs were among males working in utilities^¶¶¶ (1.15; 95% CI = 1.08–1.24) and public administration**** (1.15; 95% CI = 1.11–1.19) and among females working in public administration industries (1.12; 95% CI = 1.06–1.18). In addition, among both male and female workers, the elevated PMRs were found in health care and social assistance (1.11; 95% CI = 1.05–1.17 and 1.10; 95% CI = 1.07–1.13, respectively), and educational services industries (1.07; 95% CI = 1.02–1.12 and 1.09; 95% CI = 1.05–1.13).

Occupation

By occupation, the highest number of IPF deaths occurred among males in management (5,715; 14.4% of IPF deaths in males) and among female office and administrative support workers (4,521; 16.1% of IPF deaths in females). The highest significantly elevated PMRs were among male community and social services workers (1.23; 95% CI = 1.14–1.32) and among female farming, fishing, and forestry workers (1.24; 95% CI = 1.01–1.53). Among both male and female workers, the elevated PMRs were found in the health care practitioners and technical occupations (1.13; 95% CI = 1.06–1.21 and 1.21; 95% CI = 1.16–1.27, respectively).

Discussion

During 2020–2022, 67,843 deaths (39,712 in males and 28,131 in females) among ever-employed persons aged ≥15 years were associated with IPF. Based on an estimate that 21% of IPF deaths might be related to occupational exposures (6), approximately 14,248 deaths (8,340 in males and 5,908 deaths in females) might have been job-related. However, the estimate was based on non-U.S. reports and might not be directly applicable to the U.S. workforce.

Elevated IPF death rates among persons aged ≥75 years and males are consistent with previous reports of increased mortality in these groups (3). In contrast to findings from a previous study, the overall age-adjusted IPF death rate of 7.1 per 100,000 persons over the 3 years of this study was higher than that reported for 2017 (5.3 per 100,000) and the rates in White and non-Hispanic persons (8.2 and 7.7 per 100,00, respectively) were higher than average annual rates reported for 2004–2017 (6.1 and 6.2 per 100,000, respectively) (3). These differences could be partially explained by differences in research methodologies, improved precision in diagnostic criteria, and increasing implementation of recommendations for diagnosing IPF (1), and differences over time in the prevalences of known IPF-associated risk factors (6,7). The decrease in cigarette smoking (7) (known to be associated with IPF) among adults highlights the potentially increasing proportionate role of environmental and occupational exposures in the development of IPF (4–6).

Higher proportions of IPF deaths were observed among ever-employed persons in several industries and occupations. Among both male and female workers, the highest significantly elevated PMRs were found in the public administration, health care and social assistance, and educational services industries as well as in the health care practitioners and technical occupations. Workers in some of these industries and occupations would be anticipated to have frequent exposure to secondhand smoke^†††† (8); vapors, gas, dust, and fumes^§§§§ (8); biologic (e.g., bioaerosols in indoor environments) (2,9,10); chemical (e.g., pesticides) (5); and other hazards in the workplace (5–10). However, for some industries and occupations at increased risk, potential sources of increased risk are unclear and might be related to either work exposures or factors not directly related to work that were not fully addressed by the study design.

Limitations

The findings in this report are subject to at least eight limitations. First, no ICD-10 code is specific to IPF, and IPF might be underreported on death certificates (3). Second, the IPF diagnosis might be affected by access to specialty care and chest computed tomography, both to identify interstitial lung disease and exclude other known causes of interstitial lung disease. However, access to care information was not available, and IPF deaths were not validated using medical records. Third, because of the cross-sectional study design, no temporal relationship between IPF death and work could be measured. Fourth, information on smoking status and workplace exposures are not recorded on death certificates. Therefore, these exposures could not be evaluated for their association with IPF deaths. Fifth, the decedent’s usual industry and occupation information reported on the death certificate might not be the industry and occupation associated with IPF deaths. No work histories are recorded on death certificates to evaluate changes in employment. Sixth, multiple comparisons might identify industries and occupations with elevated PMR by chance and thus these might not actually represent occupational risk. Sixth, small sample sizes for some groups resulted in wide PMR CIs. Seventh, application of a population attributable fraction estimate from a different study population to these data is speculative and should be interpreted with caution. Finally, this was an exploratory analysis with no guiding hypotheses; therefore, these findings should be considered hypothesis-generating.

Implications for Public Health Practice

Estimates of elevated IPF mortality among ever-employed persons in certain industries and occupations suggest areas where targeted studies, and processes to identify and control causative workplace exposures according to the applicable standard might be considered.^¶¶¶¶ Primary prevention would involve using the hierarchy of controls (elimination, substitution, engineering controls, administrative controls, and personal protective equipment) to reduce or eliminate exposures to potentially causative work hazards. In addition, smoke-free workplace policies and tobacco cessation programs can help reduce or eliminate exposure to tobacco smoke. Continued research to confirm these findings, and surveillance including collection of detailed industry and occupational history and etiologic research to further characterize occupational risk factors for IPF, are essential to guide development and implementation of evidence-based interventions and policies to improve workers’ health.