A death-certificate case-control study of non-Hodgkin's lymphoma and occupation in men in North Carolina

Our plain-English summary of A death-certificate case-control study of non-Hodgkin's lymphoma and occupation in men in North Carolina, by M.C. Schumacher, E. Delzell (American Journal of Industrial Medicine, 1988).

The study

• Authors: M.C. Schumacher, E. Delzell
• Journal: American Journal of Industrial Medicine
• Published: 1988;13(3):317-30
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000272).

Abstract

A death certificate-based case-control study was performed to investigate associations between occupation and non-Hodgkin's lymphoma (NHL) in North Carolina. Cases consisted of 501 men who died of NHL (International Classification of Diseases codes 200 and 202) during the years 1968-1970, 1975-1977, and 1980-1982. Controls were selected from other noncancer deaths, and were frequency matched for age, year of death, and race. Occupation and industry were obtained from the death certificates and coded without knowledge of case-control status. An increased risk for men in professional, technical, and managerial occupations, compared with all others, was detected among whites (OR = 2.69, 1.95-3.72). Black men classified as having "low exposures" by an occupational exposure linkage system had an odds ratio of 1.74 (0.84-3.60). Because of this finding, the occupations were ranked by social class and a statistically significant linear relationship was noted in whites, with risk increasing from lower social class to upper social class. An increased risk was also detected among whites in the rubber, plastics, and synthetics industries (p = .03), and among blacks employed in machine trades occupations (OR = 3.63, 1.32-9.97) and structural work occupations (OR = 2.38, 0.93-6.05). An increased risk was also detected for black painters (p = .02), but not for whites. There was no association found between NHL and employment in the following areas: textile industry; farming; laborers; or occupations with exposures to asbestos or benzene. The association with farming was further examined in counties with high use of pesticides and herbicides, and no increased risk of NHL was detected. Cases were more likely to live in the western part of the state than the eastern. However, NHL mortality rates provided by the North Carolina State Center for Health Statistics did not confirm the relationship.

In plain English

This study used North Carolina death certificates to look for links between men's jobs and death from non-Hodgkin's lymphoma (NHL). Cases were 501 men aged 35 to 74 who died in 1968-1970, 1975-1977 or 1980-1982 with NHL on the death certificate. The 569 controls were men who had died of causes other than cancer. Jobs came from the death certificates. A job-exposure linkage system identified jobs with asbestos or benzene exposure. Results were given as odds ratios with 90% confidence limits. For asbestos-linked jobs, the odds ratio was 0.78 (0.59-1.03) in white men and 1.16 (0.58-2.30) in black men, and no increased risk was detected. No increased risk was detected for benzene-linked jobs, farming or textile work. The textile estimate for black men, 2.67 (0.98-7.29), rested on 6 cases and 5 controls. White men in professional, technical and managerial jobs had an odds ratio of 2.69 (1.95-3.72), and risk in white men rose with social class. The authors said the negative asbestos and benzene results do not rule out an association, because random errors would tend to bias results toward no effect.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Death-certificate-based case-control study
• Who was studied: Male North Carolina residents who died between their 35th and 75th birthdays with NHL on the death certificate. Of 817 eligible cases, 167 were randomly selected from each of three periods (1968-1970, 1975-1977, 1980-1982), giving 501 cases. There were 569 controls who died of non-cancer causes, frequency matched on age, year of death and race. 53 subjects with no codable occupation were excluded from the analyses.
• Exposure: Usual occupation and industry from the death certificate, coded without knowledge of case or control status. An occupation-exposure linkage system was used to classify jobs as exposed to asbestos or to benzene; moderate, high or unknown exposure levels counted as exposed. The study also looked at the textile industry, farming (including county-level pesticide and herbicide use), other industry and occupational groups, and social class.
• Main results:
  • All odds ratios were reported with 90% (not 95%) confidence limits.
  • Jobs linked to asbestos exposure covered 85 exposed cases and 99 exposed controls among white men, and 11 exposed cases and 19 exposed controls among black men.
  • Odds ratio for employment in asbestos-linked jobs, controlling for age and year of death: 0.78 (0.59-1.03) for white men and 1.16 (0.58-2.30) for black men.
  • Odds ratio for benzene-linked jobs: 0.77 (0.56-1.07) for white men and 0.94 (0.47-1.87) for black men.
  • Textile industry, adjusted for age and year of death: 0.81 (0.59-1.12) for white men and 2.67 (0.98-7.29) for black men. The result for black men rests on 6 cases and 5 controls.
  • Farmers compared with all others: 0.89 (0.64-1.25) for white men and 0.69 (0.32-1.45) for black men.
  • White men in professional, technical and managerial occupations had an increased risk, with an odds ratio of 2.69 controlling for age and year of death. The confidence limits, 1.95-3.72, are broken across a line in the body text and given intact in the abstract.
  • Among white men, risk increased with social class. The highest odds ratio, 6.23 (2.51-15.51), was in Social Class I (professionals) compared with laborers.
  • Among white men there was an increased risk in the rubber, plastics and synthetics industries, based on only four cases and no controls.
  • Among black men there was an excess of painters among cases (three cases, zero controls; p = .02).
• The authors' conclusion: The authors concluded that NHL was associated with upper social class among white men. They found no increased risk for farmers, textile workers, laborers, or jobs with asbestos or benzene exposure, and said the strong social class association may obscure detection of other risk factors.
• Limitations the authors state:
  • The authors stated that the negative results do not rule out an association of asbestos or benzene with NHL.
  • Random misclassification of occupation on death certificates, of diagnosis, and by the exposure linkage system would tend to bias results toward no effect. A more precise exposure method might give different results.
  • Social class could not be controlled for when analyzing occupational risks.
  • Death certificates gave too little detail to study specific activities or exposures within the textile industry, such as dye houses.
  • Death certificates lacked specific information on lymphoma type (histology).

Topics

Medical terms in this study, explained in our Lexicon: Case-Control Study, Death Certificate, Occupational Exposure, Odds Ratio.

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