Biomedical subjects

Patricia Stewart

Publications and source records attributed to Patricia Stewart.

11 recordsLinked to original sources

PubMed2007

Methodological issues regarding confounding and exposure misclassification in epidemiological studies of occupational exposures.

BACKGROUND: Confounding and exposure misclassification are issues that concern epidemiologists because of their potential to bias results of studies and complicate interpretations. In occupational epidemiology both are routinely raised to argue that an observed result is either a false positive or a false negative finding. Although it is important to consider the potential for limitations of epidemiologic investigations, judgment regarding their importance should be based on their actual likelihood of occurrence. METHODS: This paper is based on our experience in epidemiologic analyses and a brief review of the literature regarding confounding and exposure misclassification. RESULTS: Examples of substantial confounding are rare in occupational epidemiology. In fact, even for studies of occupational exposures and lung cancer, tobacco-adjusted relative risks rarely differ appreciably from the unadjusted estimates. This is surprising because it seems the perfect situation for confounding to occur. Yet, despite the lack of evidence that confounding is a common problem, nearly every epidemiologic paper includes a lengthy discussion on uncontrolled or residual confounding. On the other hand, exposure misclassification probably occurs in all studies. The only question is, how much? The direction and magnitude of nondifferential exposure misclassification (the type most likely to occur in cohort studies) on estimates of relative risks can be largely predicted given knowledge on the degree of misclassification, that is, relatively small amounts of misclassification can bias relative risks substantially towards the null. The literature, however, is full of discussions implying that misclassification of exposure is an explanation for a positive finding. CONCLUSIONS: These comments are not to suggest that all potential limitations for epidemiologic studies should not be considered and evaluated. We do believe, however, that the likelihood of occurrence and the direction and magnitude of the effect should be more carefully and realistically considered when making judgments about study design or data interpretation.

Age Factors↗

PubMed2006

Asthma history, occupational exposure to pesticides and the risk of non-Hodgkin's lymphoma.

We previously reported that, although asthma did not increase the risk of non-Hodgkin's lymphoma (NHL), the risk from pesticide exposures was higher among asthmatics than that among nonasthmatics. To further evaluate this finding, we analyzed data from a population-based case-control study of NHL conducted in Iowa, Detroit, Los Angeles and Seattle. Cases (n = 668) diagnosed with NHL from 1998 to 2000 and controls (n = 543) randomly selected from the same geographical areas as that of the cases were included in this analysis. Odds ratios (OR) for the risk of NHL from potential occupational exposure to pesticides tended to be higher among asthmatics (OR = 1.7; 95% CI 0.3-9.1) when compared with that among nonasthmatics (OR = 0.9; 95% CI 0.6-1.5). The risks of NHL associated with pesticide exposure were also higher among asthmatics who had history of hospitalization (OR = 2.1; 95% CI 0.2-29.0) or daily medication for asthma (OR = infinite) than those among asthmatics who did not have such histories. Our results support the previous finding that the risk of NHL from pesticide exposure may be greater among asthmatics.

Adult↗

PubMed2006

Subsequent therapy can be administered after tositumomab and iodine I-131 tositumomab for non-Hodgkin lymphoma.

BACKGROUND: Iodine I-131 tositumomab is a well tolerated and effective therapy for recurrent low-grade and transformed low-grade non-Hodgkin lymphoma (NHL). Hematologic reserve after radioimmunotherapy (RIT) is an important consideration when subsequent therapy is required. METHODS: One hundred fifty-five patients who received treatment with I-131 tositumomab were assessed, and 68 patients had progressive disease after RIT. The median age (n=68 patients) was 59 years (range,18-82 yrs), and patients received a median of 2 pre-RIT regimens (range,1-8 regimens), including 66% who received anthracycline, 19% who received platinum, and 50% who received fludarabine. RESULTS: The median time to disease progression (among progressors) was 168 days (range, 19-771 days). At the time they developed recurrent disease, patients had median white blood cell count (WBC) of 4.9 K cells/microL (range, 1.1-21.4 K cells/microL), a median absolute neutrophil count (ANC) of 3.25 K cells/microL (range, 0.59-8.20 K cells/microL), a median platelet count of 130 K cells/microL (range, 9-440 K cells/microL), and there was no significant difference between pre-RIT and recurrence values except for the platelet count (P<0.05). No patient demonstrated a WBC<1.0 K cells/microL or an ANC<0.5 K cells/microL, although 1 patient had a platelet count<10 K cells/microL. Twenty-four patients subsequently received no further chemotherapy; and, in 21 patients (88%), hematologic parameters appeared to allow subsequent chemotherapy if necessary (blood counts: National Cancer Institute Grade 0-2). Among 44 patients (65%) who received further chemotherapy (median, 2 regimens; range, 1-4 regimens), 19 patients (43%) were treated with anthracyclines, 17 patients (39%) were treated with platinum, 10 patients (23%) were treated with fludarabine, and 13 patients (30%) underwent stem cell transplantation. Disease improvement occurred in most patients, although 18 patients died (40%) after further chemotherapy, predominantly from refractory lymphoma. CONCLUSIONS: Most patients with progressive disease after treatment with iodine I-131 tositumomab were able to receive subsequent therapy, including cytotoxic chemotherapy and stem cell transplantation.

Adolescent↗

PubMed2006

A retrospective occupational cohort study of end-stage renal disease in aircraft workers exposed to trichloroethylene and other hydrocarbons.

OBJECTIVE: Case-control studies suggest hydrocarbons increase end-stage renal disease (ESRD) risk. No cohort studies have been conducted. METHODS: An occupational database was matched to the U.S. Renal Data System, and the outcome of all-cause ESRD was examined using multivariable Cox regression. Sixteen individual hydrocarbons were studied, although exposures were not mutually exclusive. RESULTS: For the 1973-2000 period, there was an approximate twofold increased risk of ESRD among workers exposed to trichloroethylene, 1,1,1-trichloroethane, and JP4 gasoline compared with unexposed subjects (all P < 0.05). Relative risk was greater than unity (P > 0.05) for several other hydrocarbons. Associations attenuated (all P > 0.05) when 2001-2002 data were included in the analyses. CONCLUSIONS: Certain hydrocarbons may increase all-cause ESRD risk. Uncertainty regarding the mechanism for increased risk and the observed attenuation in risk in 2001-2002, as well as the overlap of exposures, complicates interpretation. Additional research is needed.

Aircraft↗

PubMed2006

Estimating historical radiation doses to a cohort of U.S. radiologic technologists.

Data have been collected and physical and statistical models have been constructed to estimate unknown occupational radiation doses among 90,000 members of the U.S. Radiologic Technologists cohort who responded to a baseline questionnaire during the mid-1980s. Since the availability of radiation dose data differed by calendar period, different models were developed and applied for years worked before 1960, 1960- 1976 and 1977-1984. The dose estimation used available film-badge measurements (approximately 350,000) for individual cohort members, information provided by the technologists on their work history and protection practices, and measurement and other data derived from the literature. The dosimetry model estimates annual and cumulative occupational badge doses (personal dose equivalent) for each technologist for each year worked from 1916 through 1984 as well as absorbed doses to organs and tissues including bone marrow, female breast, thyroid, ovary, testes, lung and skin. Assumptions have been made about critical variables including average energy of X rays, use of protective aprons, position of film badges, and minimum detectable doses. Uncertainty of badge and organ doses was characterized for each year of each technologist's working career. Monte Carlo methods were used to generate estimates of cumulative organ doses for preliminary cancer risk analyses. The models and predictions presented here, while continuing to be modified and improved, represent one of the most comprehensive dose reconstructions undertaken to date for a large cohort of medical radiation workers.

Adolescent↗

PubMed2004

Occupation and bladder cancer risk in a population-based case-control study in New Hampshire.

OBJECTIVE: To identify occupations with excess bladder cancer risk in New Hampshire, where bladder cancer mortality rates have been elevated for decades. METHODS: Lifetime occupational histories were obtained from interviews with 424 cases and 645 controls in a population-based case-control study. Unconditional logistic regression models were used to estimate odds ratios (Ors) and 95% confidence intervals (CI) for each occupation, adjusted for age and smoking. Analyses by duration of employment were carried out and interactions with smoking were examined. RESULTS: Male tractor-trailer truck drivers had an elevated risk for bladder cancer (OR = 2.4, CI = 1.4-4.1), with a significant positive trend in risk with increasing duration of employment (P (trend) = 0.0003). Male metal/plastic processing machine operators also had a significant excess (OR = 4.9, CI = 1.6-15.1), attributable mainly to molding/casting machine operators (OR = 16.6, CI = 2.1-131). Elevated risk was also observed for male fabricators, assemblers, and hand workers (OR = 1.8, CI = 1.0-3.4). Women in certain sales occupations (sales clerks, counter clerks, and cashiers) had a significant excess risk (OR = 2.2, CI = 1.3-3.9) and a significant trend with duration of employment (P (trend) = 0.016), as did female health service workers (OR = 4.1, CI = 1.6-10.7; P (trend) = 0.014). There was a positive interaction between smoking and employment as a health service worker (p = 0.036). CONCLUSIONS: These findings are generally consistent with previous studies. Elevated risks for male molding/casting machine operators, female salesworkers, and female health service workers, especially those with a history of smoking, require further investigation.

Adult↗

PubMed2003

Priorities for development of research methods in occupational cancer.

Occupational cancer research methods was identified in 1996 as 1 of 21 priority research areas in the National Occupational Research Agenda (NORA). To implement NORA, teams of experts from various sectors were formed and given the charge to further define research needs and develop strategies to enhance or augment research in each priority area. This article is a product of that process. Focus on occupational cancer research methods is important both because occupational factors play a significant role in a number of cancers, resulting in significant morbidity and mortality, and also because occupational cohorts (because of higher exposure levels) often provide unique opportunities to evaluate health effects of environmental toxicants and understand the carcinogenic process in humans. Despite an explosion of new methods for cancer research in general, these have not been widely applied to occupational cancer research. In this article we identify needs and gaps in occupational cancer research methods in four broad areas: identification of occupational carcinogens, design of epidemiologic studies, risk assessment, and primary and secondary prevention. Progress in occupational cancer will require interdisciplinary research involving epidemiologists, industrial hygienists, toxicologists, and molecular biologists.

Animals↗

PubMed2002

A qualitative evaluation of questions and responses from five occupational questionnaires developed to assess exposures.

Questionnaires are increasingly being used in the workplace to assess exposures to chemicals and other agents. Although the literature contains much information on questionnaire design in general, little information is available on the challenges related to questionnaires applied to the occupational setting. Questionnaires on dry cleaning workers, nurses, farmers, car mechanics, and truck drivers were administered to a total of 25 people currently performing one of these jobs. After asking each question, the interviewer probed to identify the difficulties the respondents had in answering the questions. Overall, the respondents were able to answer the questions. Problems were found, however, with particular questions that reduced the effectiveness of the questionnaire. These included the use of unclear terms, questions open to multiple interpretations, difficult computational requirements (e.g., asking for averages for highly variable tasks), ineffective transitions between topics, and overlapping response categories. This type of testing is a crucial part of questionnaire development and can be used to effectively identify potential problems with questions and, therefore, improve them to enhance collection of higher-quality data for assessments of occupational exposures.

Humans↗

PubMed2002

Determinants of dust exposure in tunnel construction work.

In tunnel construction work, dust is generated from rock drilling, rock bolting, grinding, scaling, and transport operations. Other important dust-generating activities are blasting rock and spraying wet concrete on tunnel walls for strength and finishing work. The aim of this study was to identify determinants of dust exposure in tunnel construction work and to propose control measures. Personal exposures to total dust, respirable dust, and alpha-quartz were measured among 209 construction workers who were divided into 8 job groups performing similar tasks: drill and blast workers, shaft drilling workers, tunnel boring machine workers, shotcreting operators, support workers, concrete workers, outdoor concrete workers, and electricians. Information on determinants was obtained from interviewing the workers, observation by the industrial hygienist responsible for the sampling, and the job site superintendent. Multivariate regression models were used to identify determinants associated with the dust exposures within the job groups. The geometric mean exposure to total dust, respirable dust, and alpha-quartz for all tunnel workers was 3.5 mg/m(3) (GSD = 2.6), 1.2 mg/m(3) (GSD = 2.4), and 0.035 mg/m(3) (GSD = 5.0), respectively. A total of 15 percent of the total dust measurements, 5 percent of the respirable dust, and 21 percent of the alpha-quartz exceeded the Norwegian OELs of 10 mg/m(3), 5 mg/m(3), and 0.1 mg/m(3), respectively. Job groups with highest geometric mean total dust exposure were shotcreting operators (6.8 mg/m(3)), tunnel boring machine workers (6.2 mg/m(3)), and shaft drilling workers (6.1 mg/m(3)). The lowest exposed groups to total dust were outdoor concrete workers (1.0 mg/m(3)), electricians (1.4 mg/m(3)), and support workers (1.9 mg/m(3)). Important determinants of exposure were job group, job site, certain tasks (e.g., drilling and scaling), the presence of a cab, and breakthrough of the tunnel. The use of ventilated, closed cabs appeared to be the single most important control measure for lowering exposures.

Adult↗

PubMed2002

Comparison of two culture methods for detection of tobramycin-resistant gram-negative organisms in the sputum of patients with cystic fibrosis.

A culture method utilizing quantitative plating on antibiotic-containing media has been proposed as a technique for the detection of tobramycin-resistant organisms that is more sensitive than standard methods. Typical sputum culture methods quantitate the relative amounts of each distinct morphotype, followed by antibiotic susceptibility testing of a single colony of each morphotype. Sputum specimens from 240 cystic fibrosis patients were homogenized, serially diluted, and processed in parallel by the standard method (MacConkey agar and OF basal medium with agar, polymyxin, bacitracin, and lactose) and by plating on antibiotic-containing media (MacConkey agar with tobramycin added at 25 microg/ml [MAC-25] and 100 microg/ml [MAC-100]). MICs of tobramycin were determined for all Pseudomonas aeruginosa isolates by broth microdilution. Growth of P. aeruginosa on MAC-25 was considered to be equivalent to a tobramycin MIC of > or = 16 microg/ml, and growth on MAC-100 was considered to be equivalent to a tobramycin MIC of > or = 128 microg/ml. Analysis of method-specific detection rates showed that tobramycin-containing medium was more sensitive than the standard method for the detection of tobramycin-resistant P. aeruginosa, Stenotrophomonas maltophilia, and Achromobacter xylosoxidans but was less sensitive for the detection of Burkholderia cepacia than the standard method. When MICs for P. aeruginosa that grew on tobramycin-containing medium were tested by broth microdilution, the MICs for 28 of 121 strains (23%) growing on MAC-25 and 22 of 56 strains (39%) growing on MAC-100 were MICs < 16 and < 128 microg/ml, respectively. Addition of a tobramycin-containing MacConkey plate to the routine media for sputum culture may provide additional, clinically relevant microbiologic data.

Adolescent↗

PubMed2002

Dermal exposure assessment in occupational epidemiologic research.

Recognition of the importance of skin exposure in industrial settings has steadily increased over the last few decades. Unfortunately, the growing attention to dermal exposure in industrial hygiene has often not been reflected in the field of occupational epidemiology. An extensive literature survey was conducted to identify dermal exposure assessment methods that have been applied in epidemiologic studies. Subsequently, methodologies are postulated that could be applied to epidemiologic research. Attention is given to intensity, frequency, and duration of exposure, the exposed surface area, and personal, temporal and spatial variability in dermal exposure and uptake. It is anticipated that, in the near future, dermal exposure assessment in epidemiologic research will be based generally on expert judgment and to some degree on process-specific exposure models. Field studies collecting quantitative dermal exposure data and statistical modeling to identify exposure determinants will, however, be imperative if progress is to be made in the field of dermal exposure assessment for epidemiologic purposes.

Algorithms↗