Boiler Maker Study
Asbestos exposure and cancer mortality among petroleum refinery workers: a poisson regression analysis of updated data.
The authors investigated the relationship between asbestos exposure and respiratory cancer mortality among maintenance workers and other blue-collar workers at an Italian oil refinery. The cohort contained 931 men, 29,511 person-years, and 489 deaths. Poisson regression analysis using white-collar workers as an internal referent group provided relative risk estimates (RRs) for main causes of death, adjusted for age, age at hiring, calendar period, length of exposure, and latency. Among maintenance workers, RRs for all tumors (RR = 1.50), digestive system cancers (RR = 1.41), lung cancers (RR = 1.53), and nonmalignant respiratory diseases (RR = 1.71) were significantly increased (p < 0.05); no significant excess was found for all causes and among maintenance (RR = 1.12) and other blue-collar workers (RR = 1.01). Results confirm the increased risk of death from respiratory diseases and cancer among maintenance workers exposed to asbestos, whereas other smoking-related diseases (circulatory system) were not statistically different among groups.
WORK IN OIL REFINERIES and petrochemical plants carries with it the likelihood of exposure to various substances, most of which are considered human carcinogens. Cancer risk among oil refinery workers has, as a consequence, been the subject of a great deal of scientific literature. (1) Despite this attention, however, a thorough understanding of asbestos exposure effects on workers in this industrial sector has yet to be achieved. Although studies have long linked asbestos exposure in oil refineries and mortality for mesothelioma (which may reach 24 times above baseline, suggesting that inhalation of fibers occurred), evidence on lung cancer mortality ranges from a significant reduction in the overall population of workers (2) to a pronounced increase among blue-collar workers (3) and among maintenance workers (a large subgroup of workers involved in the use of asbestos). (4) Finally, Rosamilia et al. (5) observed nonsignificant increased odds ratios for long-term workers (25 + yr) in selected maintenance jobs (pipe, boiler).
To gain new insight into the health effects of exposure to both asbestos and other carcinogens in a recently updated Italian oil refinery cohort, we analyzed the main causes of death and adjusted the estimates for main confounding factors among three subgroups of oil refinery workers: (1) maintenance workers, (2) other blue-collar workers, and (3) white-collar workers.
Subjects and Method
Description of the cohort. The cohort consisted of 931 male workers employed in an Italian oil refinery located in La Spezia, Italy, that shut down in 1977. Company records provided information about name, gender, place and date of birth, address, identification number, job title, date of hiring, and dismissal. In the study, we included workers hired before 1977 (see Gennaro et al. (6,7) for further cohort description); none of these subjects worked less than 1 yr. We categorized workers by job title into three subgroups: (a) a reference group of 221 white-collar workers (person-years [PY] = 7,285) and two subgroups of blue-collar workers: (b) maintenance workers (n = 357; PY = 11,016) and (c) other blue-collar workers (n = 353; PY = 11,210). Our previous study (6) conducted in the same refinery showed a relevant mortality for mesothelioma among blue-collar workers (5 cases, standardized mortality ratio [SMR] = 2.03, 95% confidence interval [CI] = 0.66-4.73, local reference; SMR = 14.35, 95% CI = 4.65-33.44, national reference). We observed all cases among maintenance workers, whereas none was seen among other blue-collar workers or white-collar workers. (6) In lieu of direct exposure data, we used job title as an asbestos exposure measure, given that asbestos materials were found during the demolition of the plant.
The follow-up of workers employed in another local oil refinery (Genoa, Italy), which was included in previous analyses, (6) was not updated, given that the specific classification of their job titles was not available. Thus, we excluded this refinery from the present analysis, even if both asbestos materials and mesothelioma deaths had been detected among blue-collar workers. (6-8)
We updated the present follow-up to June 30, 1999, and the observed PY now totaled 29,511; we found 118 new deaths, and 1.5% of subjects were lost to follow-up. We ascertained the causes of death through death certificates and coded them according to the ninth revision of International Classification of Diseases. (9)
Statistical analysis. We conducted an internal comparison using white-collar workers as a reference group by using a Poisson regression model for main causes of death and for a selection of asbestos-related causes of death.
We performed Poisson regression analysis by adjusting for age (5-yr classes, 25-75+ yr), calendar period (5-yr periods, 1955-1995), age at hire (two levels: 0-24 yr, 25+ yr), length of exposure (i.e., duration of employment; three levels: 0-9 yr; 10-19 yr; 20+ yr), and latency (i.e., time since first employment; two levels: 0-19 yr; 20+ yr). We grouped data into cells according to the level of the explanatory variables.
The model was
ln([O.sub.k]) = ln([E.sub.k]) + [alpha] + [[beta].sub.i][X.sub.i] + [[epsilon].sub.k]
where [O.sub.k] are the observed deaths for a specific cause in the kth cell, and [E.sub.k] are the expected deaths in the kth cell according to age, calendar year, and cause-specific mortality rates of the Italian male population [ln() are their natural logarithms]; exp([alpha]) is the SMR with respect to Italy for persons falling in the baseline category (i.e., with all the variables set at the reference level); [X.sub.i] is a matrix of indicator variables that specify the levels of the explanatory variables defining each cell; exp([[beta].sub.i]) is a vector of unknown parameters to be estimated from the data that represent the SMR ratios related to each explanatory variable with respect to its own reference level; and [[epsilon].sub.k] is the random error. This means that the risk effects of asbestos exposure for maintenance workers and other blue-collar workers can be expressed in terms of relative risk estimates (RRs) for each cause with reference to the SMR estimated for white-collar workers. We estimated the vector of parameters and its variance-covariance matrix by using the maximum-likelihood estimation method. To fit the algorithm to the data, we set the parameters of the first level of each variable to 1.
To avoid biased estimation of the standard errors of the parameters and to improve the goodness of fit of the selected model, when the ratio between the residual deviance (DV) and its degrees of freedom (DF) was far from 1 (i.e., when there was overdispersion or underdispersion), we refitted the model by introducing the following scale parameter:
[DV.sub.MAX]/[ DF.sub.MAX]
where [DV.sub.MAX] and [DF.sub.MAX] were obtained by fitting a maximal model, that is, a model with a high level of interactions, as suggested by Aitkin et al. (10)
Results
Table 1 shows all the data of the present study, namely, the population at risk (N), observed PYs, number of deaths for main causes for the three job categories, and the RRs of maintenance workers and other blue-collar workers that we obtained by performing a Poisson regression analysis with white-collar workers as an internal reference group. We found eight cases and one case of pleural mesothelioma among maintenance workers and other blue-collar workers, respectively. No death from this disease was seen in the reference group. Although this finding prevented us from performing an internal comparison, it did confirm the high level of asbestos exposure among maintenance workers. In addition, we found one death from laryngeal cancer among maintenance workers (vs. 1.92 expected), and we observed no cases among either other blue-collar workers (vs. 1.99 expected) or white-collar workers (vs. 1.33 expected).
Maintenance workers showed significantly increased RRs (p < 0.05) for all malignant tumors (RR = 1.50), digestive tract cancers (RR = 1.41), lung cancer (RR = 1.53), and respiratory diseases (RR = 1.71). RR was not significantly increased for all causes (RR = 1.12), whereas we observed a nonsignificant decrease for circulatory system diseases (RR = 0.82). By contrast, other blue-collar workers showed RRs similar to the reference group for all causes (RR = 1.01), all malignant tumors (RR = 1.01 ), lung cancer (RR = 1.04), and circulatory system diseases (RR = 1.05), whereas we observed a nonsignificant increase for respiratory system diseases (RR = 1.22) and a nonsignificant decrease for digestive tract cancers (RR = 0.89). We could not perform a Poisson regression analysis on hemolymphopoietic neoplasms (ICD-9 = 200-208) because no death from these causes was registered among maintenance workers (vs. 3.35 expected). Among other blue-collar workers, we observed three cases, which practically equaled the expected number (3.61) when we used the Italian general population as referent (SMR = 0.83). Among white-collar workers, the SMR from hemolymphopoietic neoplasms was 1.26 (95% CI = 0.26-3.68), with three observed cases (vs. 2.38 expected).
Discussion
Only a few studies have endeavored to directly investigate the risks for asbestos-related diseases among oil refinery maintenance workers exposed to different levels of asbestos fibers. (4-8,11-14) Consequently, the debate surrounding lung cancer risk among exposed workers continues (15,16) despite strong evidence for this relationship. (4,17-19) Many articles on this subject (20-57) have been repeatedly reported and discussed elsewhere. (6,7,17,18) Therefore, we undertook this reanalysis of an updated cohort mortality study of oil refinery workers to examine the occurrence of asbestos-related diseases, chiefly lung cancer, using a more informative and powerful statistical method and taking into account previous findings that revealed a high risk for death from mesothelioma among maintenance workers. Updating the follow-up revealed eight cases of mesothelioma death in this job category, whereas we found only one case among other blue-collar workers (nearly equivalent in terms of PYs) and none among white-collar workers. This finding clearly shows which workers were exposed to asbestos. For this reason, and also to reduce the healthy worker effect, we performed an analysis using an internal referent population.
In the present analysis, RR for lung cancer was significantly increased among maintenance workers compared with white-collar workers. We also detected a significantly higher risk for all malignant tumors, digestive tract cancer, and non-neoplastic respiratory tract diseases. In addition, as reported in a previous article, (17) maintenance workers showed an increased SMR for lung cancer, significant at p < 0.10 using the Italian general population as referent, and a positive trend, not statistically significant, for length of exposure (i.e., duration of employment) and for time since first exposure (i.e., latency time). Moreover, our hypothesis of causality is strengthened because all subjects dying from lung cancer had worked in the industry for a long period (more than 6 yr), and all had a long latency period (more than 10 yr).
That other blue-collar workers--in whom the single mesothelioma death (length of employment = 24.7 yr; latency = 46.7 yr) seemingly points to a reduced asbestos exposure compared with maintenance workers--and the fact that white-collar workers shared nearly the same risk for all malignant tumors, including lung cancer deaths, could imply that in this specific subgroup the possible exposure to other occupational toxic and carcinogenic substances was probably not as important as suggested by the International Agency for Research on Cancer. (1) Because smoking is one of the main causes of both lung cancer and cardiovascular diseases, we also analyzed mortality from cardiovascular diseases. The lack of a significant difference in such diseases among the three subgroups of petroleum workers suggests that they likely had similar smoking-related habits, which are similar or lower than that of the general Italian population, as established by a previous analysis in which SMRs for cardiovascular diseases were 0.82 (95% CI = 0.58-1.12), 0.78 (95% CI = 0.58-1.01), and 0.64 (95% CI = 0.47-0.85) among white-collar, other blue-collar, and maintenance workers, respectively. (4) We can thus exclude tobacco smoking as an important confounding factor (smoking also is strictly forbidden in refineries for safety reasons). For all these reasons, all blue-collar workers should show a smoking-related mortality for respiratory tumors lower than that observed in the general population.
On the contrary, the significantly increased RRs for nonmalignant respiratory diseases observed among maintenance workers, instead of revealing a higher fraction of smokers, indicate evidence for fiber-related respiratory diseases. An analysis of these cases showed that 8 deaths among maintenance workers were due to pneumoconiosis (mean length of employment 22.5 yr; mean latency time 39.9 yr). We found no cases of pneumoconiosis among white-collar workers. Among other blue-collar workers, only two silicosis deaths (mean length of employment 34.0 yr; mean latency time 56.0 yr) were registered. These findings further substantiate our suppositions about the levels of exposure to fibers among both maintenance workers (higher) and other blue-collar workers (lower).
Cancer risk related to asbestos exposure is documented for both mesothelioma and lung cancer, as well as for other tumor sites (larynx and gastrointestinal tract). Some companies, however, have often denied that asbestos exposure is a problem, thereby hindering efforts and measures to prevent asbestos-related pathologies in specific workplaces. (19) The fact that mesothelioma is a rare, even if well-defined, neoplasm often has led to its exclusion from cohort analyses, and when an analysis was performed, no attempt was made to use this asbestos-related disease as the real (even if late) sentinel event that it is. This has consequently delayed the identification of all other asbestos related pathologies. It also has prompted the mistaken view that oil refinery workers form a homogeneous group, which in turn gives rise to a sort of "dilution effect" of the real health effects in the subgroup of workers heavily exposed to asbestos.
The use of an internal referent group as a tool to reduce the misclassification of exposures, and a statistical method able to adjust true risks according to confounding variables, strengthened the results we obtained using a classical SMR analysis. In effect, in the present study, a limitation of this approach could be an underestimate of the effects of asbestos. Because white-collar workers actually worked on the grounds of the plant, as did blue-collar workers, the observed rates (and, therefore, the differences) might be even higher.
In conclusion, using updated data and a new statistical approach, this study confirmed previous results achieved through simple statistical methods, namely SMR and attributable risk analyses. (4) In addition, this study clearly revealed that workers exposed to different levels or types of toxic agents must be categorized as accurately as possible, even when measures of exposure are not available, using job title as a simple and appropriate surrogate. Finally, for prevention purposes, we suggest that both the exposure levels of all potential toxic and carcinogenic agents and the praecox and reversible health effects be monitored regularly in all working environments.
Submitted for publication June 18, 2003; revised; accepted for publication February 2, 2004.
Dr. Montanaro is now at Ticino Cancer Registry, Cantonal Institute of Pathology, Locarno, Switzerland.
Reprint requests should be sent to Dr. Valerio Gennaro, Descriptive Epidemiology and Cancer Registry-Epidemiology and Prevention Department, National Cancer Research Institute (IST), Largo Rosanna Benzi 10, 16132 Genoa, Italy.
References
(1.) International Agency for Research on Cancer (IARC). Occupational exposures in petroleum refining; crude oil and major petroleum fuels. IARC Monogr Eval Carcinog Risk Hum 1989; 45:219-37.
(2.) Satin KP, Bailey WJ, Newton KL, et al. Updated epidemiological study of workers at two California petroleum refineries, 1950-95. Occup Environ Med 2002; 59:248-56.
(3.) Lo Presti E, Sperati A, Rapiti E, et al. Mortality study among employees at an oil refinery in Rome, Italy. Med Lav 2001; 92(5):327-37.
(4.) Gennaro V, Finkelstein MM, Ceppi M, et al. Mesotheliomas and lung tumors attributable to asbestos among oil refinery workers. Am J Ind Med 2000; 37:275-82.
(5.) Rosamilia K, Wong O, Raabe GK. A case-control study of lung cancer among refinery workers. J Occup Environ Med 1999; 41:1091-103.
(6.) Gennaro V, Ceppi M, Boffetta P, et al. Pleural mesothelioma and asbestos exposure among Italian oil refinery workers. Scand J Work Environ Health 1994; 20:213-5.
(7.) Gennaro V, Ceppi M, Fontana V, et al. Pleural mesothelioma in oil refinery workers [Author's reply]. Scand J Work Environ Health 1995; 21:303-9.
(8.) Gennaro V, Ceppi M, Fontana V, et al. Is the oil refinery plant a dangerous workplace for pleura cancer? Some epidemiological evidence. Eleventh biennial meeting of the European Association for Cancer Research. Eur J Cancer 1991; 27(suppl 3):S47.
(9.) World Health Organization (WHO). International statistical classification of diseases and related health problems--9th revision. Geneva: WHO; 1975.
(10.) Aitkin M, Anderson D, Francis B, et al. Statistical modeling in GLIM. Oxford, UK: Clarendon Press-Oxford Science Publications; 1990.
(11.) Dement JM, Hensley L, Kieding S, et al. Proportionate mortality among union members employed at three Texas refineries. Am J Ind Med 1998; 33:327-40.
(12.) Finkelstein MM. Asbestos-associated cancers in the Ontario refinery and petrochemical sector. Am J Ind Med 1996; 30:610-15.
(13.) Raabe GK, Collingwood KW, Wong O. An updated study of workers at a petroleum refinery in Beaumont, Texas. Am J Ind Med 1998; 33:61-81.
(14.) Tsai SP, Waddell LC, Gilstrap EL, et al. Mortality among maintenance employees potentially exposed to asbestos in a refinery and petrochemical plant. Am J Ind Med 1996; 29:89-98.
(15.) Bailey WJ. RE: Mesothelioma and lung tumors attributable to asbestos among petroleum workers [Am J Ind Med 2000; 37:275-82]. Am J Ind Med 2001; 39:513-4.
(16.) Tsai SP, Waddell LC, Ransdell JC. RE: Mesothelioma and lung tumors attributable to asbestos among petroleum workers [Am J Ind Med 2000; 37:275-82]. Am J Ind Med 2001; 39:515-6.
(17.) Gennaro V, Montanaro F, Ceppi M, et al. RE: Mesothelioma and lung tumors attributable to asbestos among petroleum workers [Am J Ind Med 2000; 37:275-82]. I. Reply to Tsai et al.'s Letter to the Editor and new evidence. Am J Ind Med 2001; 39:517-21.
(18.) Gennaro V, Montanaro F, Ceppi M, et al. RE: Mesothelioma and lung tumors attributable to asbestos among petroleum workers [Am J Ind Med 2000; 37:275-82]. I. Reply to Bailey's Letter to the Editor. Am J Ind Med 2001; 39:522-3.
(19.) Ludwig ER, Madeksho L, Egilman D. RE: Mesothelioma and lung tumors attributable to asbestos among petroleum workers. [Am J Ind Med 2000; 37:275-82]. Am J Ind Med 2001; 39:524-7.
(20.) Bertazzi PA, Pesatori AC, Zocchetti C, et al. Mortality study of cancer risk among oil refinery workers. Int Arch Occup Environ Health 1989; 61:261-70.
(21.) Christie D, Robinson K, Gordon I, et al. A prospective study in the Australian petroleum industry. I. Mortality. Br J Ind Med 1991; 48:507-10.
(22.) Darby GH, Dukich A, Hargens CW, et al. Information profiles on potential occupational hazards. Rockville, MD: National Institute for Occupational Safety and Health, 1978; 127-41.
(23.) De Vos Irvine H, Lamont DW, Hole DJ, et al. Asbestos and lung cancer in Glasgow and the west of Scotland. Br Med J 1993; 306:1503-6.
(24.) Divine BJ, Hartman CM, Wendt JK. Update of the Texaco mortality study 1947-1993: part II [letter]. Occup Environ Med 2000; 57:143-4.
(25.) Dodoli D, Del Nevo M, Fiumalbi C, et al. Environmental household exposures to asbestos and occurrence of pleural mesothelioma. Am J Ind Med 1992; 21:681-7.
(26.) Finkelstein MM. Maintenance work and asbestos-related cancers in the refinery and petrochemical sector. Am J Ind Med 1999; 35:201-5.
(27.) Finkelstein MM. Update of the Texaco mortality study 1947-1993: part II [letter]. Occup Environ Med 2000; 57:143-4.
(28.) Gennaro V, Fontana V, Beggi A, et al. Cox proportional hazard model in a cohort study among oil refinery workers in Genoa. Folia Oncol 1991; 14:295-302.
(29.) Gottlieb MS. Lung cancer and the petroleum industry in Louisiana. J Occup Med 1980; 22:384-8.
(30.) Hanis NM, Shallemberg LG, Donaleski DL, et al. A retrospective mortality study of workers in three major U.S. refineries and chemical plants. Part 1 : Comparisons with U.S. population. J Occup Med 1985; 27:283-92.
(31.) Hanis NM, Shallemberg LG, Donaleski DL, et al. A retrospective mortality study of workers in three major U.S. refineries and chemical plants. Part 2: Internal comparisons by geographic site, occupation, and smoking history. J Occup Med 1985; 27:361-9.
(32.) Hanis NM, Stavraky KM, Fowler JL. Cancer mortality in oil refinery workers. J Occup Med 1979; 21:167-74.
(33.) Honda Y, Delzell E, Cole P. An updated study of mortality among workers at a petroleum manufacturing plant. J Occup Environ Med 1995; 37:194-200.
(34.) Kaplan SD. Update of a mortality study of workers in petroleum refineries. J Occup Med 1986; 28:514-6.
(35.) Kriebel D, Wegman DH, Moure-Eraso R, et al. Limitations of meta-analysis: cancer in the petroleum industry. Am J Ind Med 1990; 17:269-71.
(36.) Levin LI, Silverman DT, Hartge P, et al. Smoking patterns by occupation and duration of employment. Am J Ind Med 1990; 17:711-25.
(37.) Lilis R, Daum S, Anderson H, et al. Asbestosis among maintenance workers in the chemical industry and oil refinery workers. In: Biological effects of mineral fibers. IARC Scientific Publication No. 30. Lyon, France: International Agency for Research on Cancer, 1980; pp 795-810.
(38.) Liveright T, Gann P, McAna J. Health hazard evaluation report no. HETA 81-372-1727, Exxon Corporation, Bayway Refinery and Chemical Plant, Linden, New Jersey. Cincinnati, OH: National Institute for Occupational Safety and Health, 1986.
(39.) Mehlman MA. Dangerous and cancer causing properties of products and chemicals in the oil-refining and petrochemical industries. Part IX: asbestos exposure and analysis of exposure. Ann NY Acad Sci 1991; 643:368-88.
(40.) Mehlman MA. Dangerous and cancer causing properties of products and chemicals in the oil refining and petrochemical industry: part V. Asbestos-caused cancers and exposure of workers in the oil refining industry. Toxicol Ind Health 1991; 7:53-71.
(41.) Nelson NA, Barker DM, Van Peenen PFD, et al. Determining exposure categories for a refinery retrospective cohort mortality study. Am Ind Hyg Assoc J 1983; 46:653-7.
(42.) Nicholson WJ, Perkel G, Selikoff IJ. Occupational exposure to asbestos: population at risk and projected mortality: 1980-2030. Am J Ind Med 1982; 3:259-311.
(43.) Pearce N, Matos E, Vainio H, et al. Occupational cancer in developing countries. IARC Scientific Publication No. 129. Lyon, France: International Agency for Research on Cancer, 1994.
(44.) Rushton L. Further follow up of mortality in United Kingdom oil refinery cohort. Br J Ind Med 1993; 50:549-60.
(45.) Schnatter AR, Theriault G, Katz AM, et al. A retrospective mortality study within operating segments of a petroleum company. Am J Ind Med 1992; 22:209-29.
(46.) Smyth NPD, Goodman NG, Basu AP, et al. Pulmonary asbestosis. Chest 1971; 60(3):270-3.
(47.) Tozzi GA, Parello G. I livelli di esposizione ad amianto in una raffineria di petrolio [I levels of asbestos exposure in a petroleum refinery]. Official Report. Genoa, Italy: AUSL3. 1995.
(48.) Tsai SP, Gilstrap EL, Cowles SR, et al. Long-term follow-up mortality study of petroleum refinery and chemical plant employees. Am J Ind Med 1996; 29:75-87.
(49.) Tsai SP, Waddell LC, Gilstrap EL, et al. Mortality among maintenance employees potentially exposed to asbestos in a refinery and petrochemical plant. Am J Ind Med 1996; 29:89-98.
(50.) Van Peenen PFD, Blanchard AG, Wolkonscky PM. Smoking habits of oil refinery workers. Am J Public Health 1984; 874:1408-9.
(51.) Von Bittersohl G, Ose H. Zur epidemiologie des pleuramesothelioma [On the epidemiology of pleuramesothelioma]. Z Ges Hyg 1971; 861-4.
(52.) Von Bittersohl G. Epidemiologische untersuchungen uber Krebserkrankungen in der chemischen industrie [An epidemiological investigation of cancer in the chemical Industry]. Arch Geschwulstforsch 1971; 38:198-209.
(53.) Wong O, Raabe GK. Critical review of cancer epidemiology in petroleum industry employees, with a quantitative meta-analysis by cancer site. Am J Ind Med 1989; 15:283-310.
(54.) Wong O. Pleural mesothelioma in oil refinery workers [letter]. Scand J Work Environ Health 1995; 21:301-3.
(55.) Zadeic G. A cohort study of occupational asbestos exposure related neoplasms in Texas Gulf coast area. Diss Abst Int 1988; 49(4):1118-B.
(56.) Lewis RJ, Schnatter AR, Drummond I, et al. Mortality and cancer morbidity in a cohort of Canadian petroleum workers. Occup Environ Med 2003; 60:918-28.
(57.) Gun RT, Pratt NL, Griffith EC, et al. Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry. Occup Environ Med 2004; 61(2):150-6.
FABIO MONTANARO
MARCELLO CEPPI
RICCARDO PUNTONI
Epidemiology and Biostatistics
National Cancer Research Institute
Genoa, Italy
STEFANIA SILVANO
Occupational Hygiene and Safety Department
AUSL5
La Spezia, Italy
VALERIO GENNARO
Descriptive Epidemiology and Cancer
Registry-Epidemiology and Prevention Department
National Cancer Research Institute
Genoa, Italy
E-mail: valerio.gennaro@istge.it
Table 1.--Number of Workers (N), Cases, Person-Years (PY), and Relative
Risk Estimates (RRs), with 95% Confidence Intervals (95% CI), among
Maintenance Workers and Other Blue-Collar Workers Compared with
White-Collar Workers in a Petroleum Refinery
Reference
n = 221 (PY = 7,285)
Causes of death (ICD-9) Cases RR *
All causes (000-999) 118 1.00
All malignant tumors (140-208) 34 1.00
Digestive system cancers (150-159) 13 1.00
Larynx (161) ([section]) 0 --
Lung (162) 11 1.00
Pleura (163) ([section]) 0 --
Respiratory tract diseases (460-519) (#) 9 1.00
Circulatory system diseases (390-459) 48 1.00
Maintenance workers
n = 357 (PY = 11,016)
Causes of death (ICD-9) Cases RR * 95% CI
All causes (000-999) 196 1.12 0.95-1.33
All malignant tumors (140-208) 74 1.50 1.18-1.90
Digestive system cancers (150-159) 27 1.41 1.07-1.87
Larynx (161) ([section]) 1 -- --
Lung (162) 24 1.53 1.11-2.10
Pleura (163) ([section]) 8 -- --
Respiratory tract diseases (460-519) (#) 23 1.71 1.23-2.38
Circulatory system diseases (390-459) 58 0.82 0.66-1.02
Other blue-collar workers
n = 353 (PY = 11,210)
Causes of death (ICD-9) Cases RR * 95% CI
All causes (000-999) 175 1.01 0.85-1.20
All malignant tumors (140-208) 51 1.01 0.78-1.30
Digestive system cancers (150-159) 17 0.89 0.66-1.22
Larynx (161) ([section]) 0 -- --
Lung (162) 17 1.04 0.75-1.46
Pleura (163) ([section]) 1 -- --
Respiratory tract diseases (460-519) (#) 16 1.22 0.86-1.72
Circulatory system diseases (390-459) 74 1.05 0.86-1.29
* RRs adjusted for age, age at hiring, calendar period, length of
exposure, and latency.
([section]) No case was detected in the reference group.
(#) Including two and eight deaths from pneumoconiosis among other
blue-collar and maintenance workers, respectively.