About the Essential Worker Code Set

Purpose: To identify workers in essential critical infrastructure industries as defined by the Department of Homeland Security – Cybersecurity and Infrastructure Security Agency (DHS-CISA) using standardized industry codes to support public health interventions, data collection, and analyses related to the COVID-19 pandemic and other public health crises.

Background: CISA has published four versions of an advisory list identifying essential critical infrastructure workers to inform state and local shutdown orders and industry-level occupational health decisions during the COVID-19 response. The advisory list has also been widely applied as the best approximation of a national definition of essential workers in research studies but has not been mapped to standardized codes for use from a public health perspective. Standardized codes are required to readily identify worker populations in new and existing public health data sources.

Approach: We used the Federal Reserve Bank of Philadelphia’s list of North American Industry Classification System (NAICS) codes and essential industry designations corresponding to v3.0 of the CISA advisory list as a starting point for development of an updated list mapping v4.0 designations to Census industry codes (CICs). We identified essential industry designations corresponding to v4.0 of the CISA advisory list for all six-digit NAICS codes, used the Quarterly Census of Employment and Wages to estimate worker population by six-digit NAICS industry, and cross-walked NAICS codes and essential industry designations to CICs. We also applied the Employed Labor Force Query System to estimate numbers of U.S. workers in each Census industry overall and by Census industry and occupation pair.

The Department of Homeland Security Cybersecurity and Infrastructure Security Agency (CISA) is charged with securing and protecting critical infrastructure in the United States. Under this mandate, they developed multiple versions of an advisory list describing essential critical infrastructure workers (ECIWs).¹ The list includes those who “conduct a range of operations and services that are typically essential to continued critical infrastructure viability” during the COVID-19 pandemic.¹ Early versions of this list identified essential worker roles and ensured that ECIWs could access workplaces during stay-at-home orders.¹ The most recent CISA advisory list, “Guidance on the Essential Critical Infrastructure Workforce: Ensuring Community and National Resilience in COVID-19 Response Version 4.0,” was released August 18^th, 2020 to identify workforce populations within 18 industry sectors (e.g., Healthcare/Public Health, Education, etc.) that may require specialized occupational risk management strategies or be priorities for allocation of limited public health resources.¹ The series of CISA advisory lists have informed state and local shutdown orders, industry-level occupational health decisions, and vaccination allocation strategies.^2-5

Interpretation of the CISA advisory list by public health practitioners and researchers has been complicated by its inclusion of a mixture of whole industries, specific occupations, and industrial supply chains. The advisory list does not include standard industry or occupation titles or codes used to identify workers in population-based reference data. However, several outside groups have published complementary lists of titles and codes.^6-8 The Brookings Institution mapped the CISA advisory list to 121 North American Industry Classification System (NAICS) titles and codes to correspond to v1.0.⁶ The Federal Reserve Bank of Philadelphia produced similar lists of NAICS codes corresponding to v1.0, v2.0, and v3.0 of the CISA advisory list, as well as lists of NAICS codes corresponding to some state-specific executive orders and reopening timelines.⁷ The Labor Market Information Institute also published a list of Standard Occupational Classification (SOC) titles and codes corresponding to v1.0 of the CISA advisory list.⁸ These code lists have been valuable resources for researchers evaluating impacts of the pandemic on workers designated as essential and non-essential.^9,10

Epidemiological analyses evaluating industry and occupation as exposures or covariates of interest, as well as work as a social determinant of health, commonly apply Census industry codes (CICs) and Census occupation codes (COCs). These classifications are derived from but are broader than NAICS and SOC and are often nested, such that some Census occupations may only occur within specific Census industries.¹¹ CICs and COCs are often used to identify worker populations in and are required to link across resources used for public health research and planning.¹¹ Thus, there is a need for an updated, comprehensive mapping of the CISA advisory list from a public health perspective to enable meaningful and robust public health interventions and assessments. Specifically, an industry-based approach using both NAICS codes and CICs is well suited to capture the full breadth of the ECIW population, ensuring that all workers within essential critical infrastructure industries are identified regardless of their exact occupations.

We produced lists of NAICS and Census industry titles and codes corresponding to the most recent version of the CISA advisory list for use by public health researchers and practitioners who are charged with identifying essential workers in public health data. The lists may be applied in whole to identify broad populations of workers who may have been required to continue working throughout the COVID-19 crisis on a national level or adapted to identify state- or city-specific ECIW populations. They may also be applied in part to study specific sectors of the essential critical infrastructure workforce as defined by CISA.

The Advisory Committee on Immunization Practices (ACIP) has recommended that COVID-19 vaccination be offered to essential workers, including healthcare personnel in Phase 1a, frontline essential workers in Phase 1b, and all other essential workers identified by CISA in Phase 1c.^4,5 An adapted extract from a preliminary version of the coding guide developed here has been released to support jurisdictions in identification of these essential worker populations for vaccination prioritization.¹²

We applied the Federal Reserve Bank of Philadelphia’s list of NAICS codes and essential industry designations⁵ corresponding to v3.0¹³ of the CISA advisory list as a starting point for development of an updated list corresponding to v4.0 using CICs. We identified essential industry designations corresponding to v4.0 of the CISA advisory list¹ for all six-digit 2017 NAICS codes¹⁴ and noted the CISA essential critical infrastructure workforce sector and sector-based major bullet number under which each essential industry was identified. We also drew population estimates for each six-digit NAICS industry using the Quarterly Census of Employment and Wages (QCEW). Next, we cross-walked NAICS codes and essential industry designations to 2012 CICs¹⁵ and identified each CIC as “Essential”, “Non-essential,” or “Mixed Essential/Non-essential” according to the essential industry designations of the component NAICS codes. Finally, we applied the Employed Labor Force Query (ELF) System to estimate numbers of U.S. workers in each Census industry overall and by Census industry and occupation pair as a foundation for public health researchers and practitioners evaluating COVID-19-related factors by both industry and occupation.

The resources included in this coding guide are summarized in Table 1. A detailed description of the methods applied to develop these resources is also available. Download the excel spreadsheets or .csv files containing NAICS industry titles and codes, Census industry titles and codes, essential industry designations corresponding to v4.0 of the CISA advisory list on the essential critical infrastructure workforce, and population estimates by six-digit NAICS industry, Census industry, and Census industry-occupation pair.

Bureau of Labor Statistics (BLS); Census industry code (COC); Census occupation code (COC); Cybersecurity and Infrastructure Security Agency (CISA); Essential industry designation (EID); Employed Labor Force (ELF); North American Industry Classification System (NAICS); Quarterly Census of Employment and Wages (QCEW)

Work is a core social determinant of health,¹⁶ and the ongoing COVID-19 pandemic has created and highlighted distinctions that impact worker health: essential and non-essential workers,6-8 workers who can and cannot work from home,¹⁷ workers who remain employed and those experiencing unemployment,18 and workers potentially exposed to or able to avoid exposure to COVID-19 at work.^10,19 Public health researchers and practitioners have raced to respond to these interconnected factors in the context of the pandemic by characterizing COVID-19 vulnerability,²⁰ incidence,²¹ and downstream effects²² among specific worker populations, developing guidelines to reduce occupational transmission,^23,24 and devising mechanisms to allocate scarce public health resources equitably.^3-5 Much of this work has focused on essential workers. The CISA advisory list outlining the essential critical infrastructure workforce¹ has been widely applied as the best approximation of a national definition for essential workers but has not been specifically coded for use from a public health perspective. We hope that the resources provided in this coding guide may be useful in whole or part to public health professionals’ ongoing efforts related to COVID-19 and essential workers.

The CISA advisory list provides text descriptions of worker roles within a set of 18 high-level sectors deemed critical infrastructure or supporting critical infrastructure1 and has been updated several times in response to discussions around phased closure and reopening. CISA also sought continuing input from external stakeholders, including federal agency partners, industry experts, and state and local government officials.¹ The CISA advisory list has broadly informed state-level shutdown orders; some states have closely adopted one version of the list or updated their orders with the release of new versions, while others have devised similar but unconnected orders.^2,7 The authors emphasize that this list is not a federal directive or standard and should not be considered the exclusive list of critical infrastructure sectors or essential worker roles during the COVID-19 response. Rather, they highlight the need for individual jurisdictions to adapt the advisory list to meet community needs.¹

The coding guide developed here applies industry codes to capture all essential critical infrastructure workers (ECIWs), regardless of occupation. As an example of this approach, the ACIP recommended that healthcare personnel be offered COVID-19 vaccination in Phase 1a.⁴ Healthcare personnel are defined to include not only workers in healthcare occupations, but also support staff in healthcare settings who may experience direct or indirect exposure to infectious patients or materials (e.g. environmental, food, and administrative services). Occupations of essential workers may occur in more than one industry, and because CISA primarily catalogs ECIWs by industry, ECIWs cannot be identified by occupation alone. For instance, many workers in grocery stores hold occupations that are common within both essential and non-essential retail settings. Identification of these workers by industry ensures that they are appropriately classified according to the CISA guidance. This approach also allows for site-based research studies and intervention designs among ECIWs. Potential applications could include on-site vaccination campaigns to reach all workers at manufacturing plants or a serology study among all school employees within a single school district.

Although the CISA advisory lists and state and local shutdown orders have largely focused on designation of essential industries, workers within these industries may face varying COVID-19 exposure potential. The Brookings Institution defined frontline workers as those “within essential industries who must physically show up to their jobs”.²⁵ The National Academies of Sciences, Engineering, and Medicine made a similar distinction in their framework for equitable allocation of a COVID-19 vaccine, defining critical workers in high-risk settings as “workers in industries essential to the functioning of society and at substantially higher potential for exposure,” where risk of exposure is determined by inability to work from home or otherwise isolate from potential exposure at work.³ Ability to work from home and potential COVID-19 exposure potential by occupation have been repeatedly characterized.^10,19,25-28 We encourage use of the resources in this coding guide in conjunction with supplemental data sources, including Occupational Information Network (O*NET), American Community Survey Public Use Microdata (ACS PUMS), and BLS Occupational Requirement Survey, to further evaluate ability to work from home, infection exposure risk, workforce composition, vaccination coverage, and infection incidence by occupation within essential critical infrastructure industries as defined by CISA.

This coding guide is subject to several limitations. Our purpose is not to speculate on reasons for inclusion or non-inclusion of specific worker roles in the original CISA guidance, but to map the CISA descriptions to standardized industry codes. Some six-digit NAICS industries include both essential and non-essential sub-industries; we designated NAICS codes as essential if they contained any sub-industries that corresponded to ECIW descriptions. As a result, some non-essential sub-industries may be included. Further, mapping of these text descriptions to NAICS and Census codes may be subject to interpretation and other mapping approaches may produce slight differences in essential industry designations.^6,7 Experts in industry and occupation coding and CISA representatives reviewed all designations to minimize this possibility. Population estimates given for six-digit NAICS industries and CICs are drawn from separate data sources using the most recent data available in each and do not align exactly due to disparate inclusion criteria in each data source. Limitations of each data source are described here.

The COVID-19 pandemic and response have created new challenges for public health researchers and practitioners striving to protect workers and their communities. As new interventions are introduced, further efforts are needed to swiftly identify potential recipients and evaluate intervention impact on worker populations. Retrospective analyses will also provide valuable insights into the successes and failures of measures taken to prevent occupational transmission of COVID-19, informing preparations for future epidemics. We hope that the resources shared in this coding guide may support these efforts.

1. Cybersecurity and Infrastructure Security Agency. Advisory memorandum on ensuring essential critical infrastructure workers ability to work during the COVID-19 response. Washington, D.C.: US Department of Homeland Security, CISA; 2020.
2. Humphreys BE. COVID-19: State and local shut-down orders and exemptions for critical infrastructure. Washington, D.C.: Library of Congress, Congressional Research Service; 2020.
3. National Academies of Sciences, Engineering, and Medicine. Framework for equitable allocation of COVID-19 vaccine. Washington, D.C.: The National Academies Press; 2020.
4. Dooling K, McClung N, Chamberland M, et al. The Advisory Committee on Immunization Practices’ Interim Recommendation for Allocating Initial Supplies of COVID-19 Vaccine — United States, 2020. Morb Mortal Wkly Rep 2020; 69(49): 1857-1859.
5. Dooling K, Marin M, Wallace M, et al. The Advisory Committee on Immunization Practices’ Updated Interim Recommendation for Allocation of COVID-19 Vaccine — United States, December 2020. Morb Mortal Wkly Rep 2020; 69: 1657-1660.
6. Tomer A, Kane JW. How to protect essential workers during COVID-19. The Brookings Institution; 2020.
7. Atalay E, Fujita S, Mahadevan S, et al. Reopening the economy: What are the risks, and what have states done? Philadelphia, PA: Federal Reserve Bank of Philadelphia; 2020.
8. Cook W. Many US workers in critical occupations in the fight against COVID-19 (Revised). LMI Institute; 2020.
9. McCormack G, Avery C, Spitzer AK, et al. Economic vulnerability of households with essential workers. JAMA 2020; 324(4): 388-390.
10. Hawkins D. Differential occupational risk for COVID-19 and other infection exposure according to race and ethnicity. Am J Ind Med 2020; 63: 817-820.
11. US Census Bureau. American Community Survey: Recent changes in the Census industry and occupation classification systems. Technical Paper 78, March 2020. Suitland, MD: US Department of Commerce, US Census Bureau; 2020.
12. Centers for Disease Control and Prevention. Interim List of Categories of Essential Workers Mapped to Standardized Industry Codes and Titles. Atlanta, GA: US Department of Health and Human Services, CDC; 2020.
13. Cybersecurity and Infrastructure Security Agency. Advisory memorandum on identification of essential critical infrastructure workers during COVID-19 response. Washington, D.C.: US Department of Homeland Security, CISA; 2020.
14. Office of Management and Budget. North American Industry Classification System: United States, 2017. Washington, D.C.: Executive Office of the President, OMB; 2017.
15. US Census Bureau. Industry and Occupation Code Lists & Crosswalks. Suitland, MD: US Department of Commerce, US Census Bureau; 2020.
16. Quinn Ahonen E, Fujishiro K, Cunningham T, et al. Work as an Inclusive Part of Population Health Inequities Research and Prevention. Am J Pub Health 2018; 108(3): 306-311.
17. Angelucci M, Angrisani M, Bennet DM, et al. Remote Work and the Heterogeneous Impact of COVID-19 on Employment and Health. Cambridge, MA: National Bureau of Economic Research; 2020.
18. Montenovo L, Jiang X, Lozano Rojas F, et al. Determinants of Disparities in Covid-19 Job Losses. Cambridge, MA: National Bureau of Economic Research; 2020.
19. Zhang M. Estimation of differential occupational risk of COVID‐19 by comparing risk factors with case data by occupational group. Am J Ind Med 2020; 1-9.
20. Silver SR, Li J, Boal WL, et al. Prevalence of Underlying Medical Conditions Among Selected Essential Critical Infrastructure Workers — Behavioral Risk Factor Surveillance System, 31 States, 2017–2018. Morb Mortal Wkly Rep 2020; 69(36): 1244-1249.
21. Mutambudzi M, Niedzwiedz CL, Macdonald EB, et al. Occupation and risk of severe COVID-19: prospective cohort study of 120,075 UK Biobank participants. Occ Environ Med 2020.
22. Pearman A, Hughes ML, Smith EL, et al. Mental Health Challenges of United States Healthcare Professionals During COVID-19. Front Psychol 2020; 11: 2065.
23. Centers for Disease Control and Prevention. Interim guidance for businesses and employers responding to coronavirus disease 2019 (COVID-19), May 2020. Atlanta, GA: US Department of Health and Human Services, CDC; 2020.
24. Occupational Safety and Health Administration. Guidance on preparing workplaces for COVID-19. Washington, D.C.: US Department of Labor, OSHA; 2020.
25. Tomer A, Kane JW. To protect frontline workers during and after COVID-19, we must define who they are. The Brookings Institution; 2020.
26. Mongey S, Pilossoph L, Weinberg A. Which workers bear the burden of social distancing policies? Cambridge, MA: National Bureau of Economic Research; 2020.
27. Baker MG. Nonrelocatable Occupations at Increased Risk During Pandemics: United States, 2018. Am J Pub Health 2020; 110(8): 1126-1132.
28. Dingel JI, Neiman B. How many jobs can be done at home? Cambridge, MA: National Bureau of Economic Research; 2020.