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Biomedical subjects

J F Boivin

Publications and source records attributed to J F Boivin.

At least 19 recordsLinked to original sources
PubMed1998

Screening for prostate cancer: estimating the magnitude of overdetection.

BACKGROUND: No randomized controlled trial of prostate cancer screening has been reported and none is likely to be completed in the near future. In the absence of direct evidence, the decision to screen must therefore be based on estimates of benefits and risks. The main risk of screening is overdetection--the detection of cancer that, if left untreated, would not cause death. In this study the authors estimate the level of overdetection that might result from annual screening of men aged 50-70. METHODS: The annual rate of lethal screen-detectable cancer (detectable cancer that would prove fatal before age 85 if left untreated) was calculated from the observed prostate cancer mortality rate in Quebec; the annual rate of all cases of screen-detectable prostate cancer was calculated from 2 recent screening studies. RESULTS: The annual rate of lethal screen-detectable prostate cancer was estimated to be 1.3 per 1000 men. The annual rate of all cases of screen-detectable prostate cancer was estimated to be 8.0 per 1000 men. The estimated case-fatality rate among men up to 85 years of age was 16% (1.3/8.0) (sensitivity analysis 13% to 22%). INTERPRETATION: Of every 100 men with screen-detected prostate cancer, only 16 on average (13 to 22) could have their lives extended by surgery, since the prostate cancer would not cause death before age 85 in the remaining 84 (78 to 87).

Aged↗
PubMed1998

Selection of controls in database case-control studies: glucocorticoids and the risk of glaucoma.

In case-control studies conducted using computerized databases, controls are often selected as a random sample from the base population. This representative choice of controls is intended to guard against selection bias. We show, using data from a database case-control study, that such a definition of controls may also lead to selection bias under two conditions: (1) if the target disease has a prolonged asymptomatic clinical course with its detection depending on a specific physical examination and (2) if exposed patients have a higher likelihood of having the disease detected than unexposed patients. The extent of the bias that could result from the use of randomly selected controls was investigated in the context of a case-control study of the risk of ocular hypertension or glaucoma associated with the use of glucocorticoids, conducted using the Quebec universal health insurance computerized databases. This article also illustrates that a computerized database can be useful to empirically explore opportunities for bias.

Aged↗
PubMed1998

Controlling confounding when studying large pharmacoepidemiologic databases: a case study of the two-stage sampling design.

Large drug databases have been the source of interesting developments for pharmacoepidemiologic research, because they provide relatively accurate drug exposure histories. An important limitation of these databases is the lack of information on potential confounders. One solution, developed more than a decade ago but not widely used, is "two-stage sampling," in which stage 1 is the collection of information on drug exposure and outcomes, and stage 2 is the collection of confounder data on a subset of the stage 1 sample. The balanced design, wherein an equal number of individuals is selected from each drug exposure/disease category, is usually the most efficient strategy by which to select the stage 2 sample. We illustrate the efficiency of the balanced design in two-stage sampling using data from a provincial health organization and a simulation. We also evaluate the relative importance of factors affecting the precision of the effect estimate of the exposure of interest.

Case-Control Studies↗
PubMed1998

First treatment with inhaled corticosteroids and the prevention of admissions to hospital for asthma.

BACKGROUND: Early treatment with inhaled corticosteroids appears to improve clinical symptoms in asthma. Whether a first treatment initiated in the year following the recognition of asthma can prevent major outcomes such as admission to hospital has yet to be studied. METHODS: A case-control study nested within a cohort of 13,563 newly treated asthmatic subjects selected from the databases of Saskatchewan Health (1977-1993) was undertaken to investigate the effectiveness of a first treatment with inhaled corticosteroids in preventing admissions to hospital for asthma. Study subjects were aged between five and 44 years at cohort entry. First time users of inhaled corticosteroids were compared with first time users of theophylline for a maximum of 12 months of treatment. The two treatments under study were further classified into initial and subsequent therapy to minimize selection bias and confounding by indication. Odds ratios associated with hospital admissions for asthma were estimated using conditional logistic regression. Markers of asthma severity, as well as age and sex, were considered as potential confounders. RESULTS: Three hundred and three patients admitted to hospital with asthma were identified and 2636 matched controls were selected. subjects initially treated with regular inhaled corticosteroids were 40% less likely to be admitted to hospital for asthma than regular users of theophylline (odds ratio 0.6; 95% CI 0.4 to 1.0). The odds ratio decreased to 0.2 (95% CI 0.1 to 0.5) when inhaled corticosteroids and theophylline were given subsequently. CONCLUSION: The first regular treatment with inhaled corticosteroids initiated in the year following the recognition of asthma can reduce the risk of admission to hospital for asthma by up to 80% compared with regular treatment with theophylline. This is probably due, at least in part, to reducing the likelihood of a worsening in the severity of asthma.

Administration, Inhalation↗
PubMed1998

Inhaled corticosteroids and the prevention of readmission to hospital for asthma.

Despite the proven efficacy of inhaled corticosteroids in reducing airway inflammation and their increasing use for the treatment of asthma since the mid 1980s, hospitalization for asthma has been increasing in frequency in several countries. Only few studies, reporting contradictory results, have investigated the role of inhaled corticosteroids in the prevention of hospitalizations for asthma. Using a cohort of 2,059 hospitalized asthmatic patients between 5 and 54 yr of age, we estimated the effectiveness of inhaled corticosteroids in preventing a readmission to hospital for asthma as a function of the duration of therapy. The cohort was selected from the databases of Saskatchewan Health from 1977 to 1993. The rate ratio (RR) of a readmission for asthma varied with duration of regular therapy with inhaled corticosteroids. During the first 15 d of regular therapy, users of inhaled corticosteroids were as likely as nonusers of these medications to be readmitted for asthma with a RR of 1.2 (95% CI: 0.8-1.8). Subjects treated regularly with inhaled corticosteroids for at least 16 d and as long as 6 mo were 40% less likely to be readmitted for asthma (RR = 0.6; 95% CI: 0.4-0.9), while after 6 mo of regular treatment the protective effect disappeared (RR = 1.3; 95% CI: 0.7-2.4). We conclude that regular therapy with inhaled corticosteroids can substantially reduce the risk of a readmission for asthma after only 15 d of use. Confounding by severity appears as the most likely explanation for the disappearance of the beneficial effect after 6 mo of regular therapy.

Administration, Inhalation↗
PubMed1998

External comparisons from nested case-control designs.

The nested case-control design, used to sample within cohorts, is usually employed for internal comparisons. We propose to use this design for external comparisons. We present two probability-weighted estimators of the expected number of cases under a given exposure, based on external rates, for two versions of the nested case-control design. These estimators are used, along with their variance estimators, to form confidence intervals for standardized mortality ratios. The estimators are practically unbiased, whereas the naive estimator that treats the nested case-control sample as a random sample of the cohort is clearly biased. An estimator from the alternative Cox model-based approach is found to be substantially biased when applied in this context. Comparing the proposed estimators for nested case-control designs to a corresponding estimator for the case-cohort design, we found that the correlation between follow-up time and exposure time (that is, the amount of time under the exposure effect) has an impact on which type of design is more efficient for external comparisons. A small correlation favors the case-cohort design and a large correlation the nested case-control design. We examine empirical properties of these estimators through computer simulations, using a cohort study of the incidence of second cancer in 2,189 patients with Hodgkin's disease.

Bias↗
PubMed1997

Risk of ocular hypertension or open-angle glaucoma in elderly patients on oral glucocorticoids.

BACKGROUND: Ocular hypertension and open-angle glaucoma are well-known side-effects of treatment with topical ophthalmic glucocorticoids. There is uncertainty about the risk of these disorders with oral glucocorticoid therapy. METHODS: Data from the Quebec universal health insurance programme for the elderly were used to identify 9793 patients with a new diagnosis of ocular hypertension or open-angle glaucoma, or on newly prescribed treatment for these disorders (cases). 38,325 controls were randomly selected from ophthalmology patients seen in the same month and year as the case (index date). Current use of oral glucocorticoids was defined as that within 14 days of the index date. All glucocorticoid doses were converted to the equivalent amount of hydrocortisone. The case-control analysis was done by conditional logistic regression and adjusted for age, sex, systemic hypertension, diabetes mellitus, ophthalmic glucocorticoids, glucocorticoid injections, and variables related to general health. FINDINGS: The mean ages of cases and controls were similar (74.9 [SD 6.3] vs 74.7 [6.4]). The adjusted odds ratio of ocular hypertension or open-angle glaucoma for current users of oral glucocorticoids compared with non-users was 1.41 (95% CI 1.22-1.63). There was a dose-related increase in the adjusted odds ratios for current users: 1.26 (1.01-1.56) for less than 40 mg per day of hydrocortisone, 1.37 (1.06-1.76) for patients on 40-79 mg per day, and 1.88 (1.40-2.53) for patients on 80 mg or more per day. The odds ratios also increased with the duration of treatment over the first 11 months of exposure. INTERPRETATION: The use of oral glucocorticoids increases the risk of ocular hypertension or open-angle glaucoma in elderly patients. In patients in this age-group who need long-term treatment with high doses of oral glucocorticoids, monitoring of intraocular pressure may be justified.

Administration, Oral↗
PubMed1997

Benzodiazepine use and the risk of motor vehicle crash in the elderly.

CONTEXT: Benzodiazepines, used by a sizable number of the elderly population, may affect the ability to drive and thus increase the risk of a motor vehicle crash. Epidemiologic studies of this question have produced inconsistent results that may be due to the different effects of long- and short-half-life benzodiazepines and variations in their duration of use. OBJECTIVE: To determine whether the use of benzodiazepines of either long- or short-elimination half-life is associated with the risk of injurious motor vehicle crash in the elderly. DESIGN AND SETTING: Nested case-control design within a cohort of 224,734 drivers from the Canadian province of Quebec, aged 67 to 84 years, followed up from 1990 to 1993. Computerized data for the study were obtained from provincial driver's license files, police reports of injurious crashes, and health insurance records. PATIENTS: We identified all 5579 drivers involved in an injurious crash (cases) and a random sample of 10 controls per case selected from a subcohort of 13,256 subjects. MAIN OUTCOME: Involvement of a cohort member as a driver in a motor vehicle crash in which at least 1 person (not necessarily the driver) sustained bodily injury. RESULTS: The adjusted rate ratio of crash involvement within the first week of long-half-life benzodiazepine use was 1.45 (95% confidence interval [CI], 1.04-2.03). The rate ratio for continuous use of longer duration up to 1 year was slightly lower but remained significant (rate ratio, 1.26; 95% CI, 1.09-1.45). In contrast, there was no increased risk after the initiation of treatment with short-half-life benzodiazepines (rate ratio, 1.04; 95% CI, 0.81-1.34) or with their continued use (rate ratio, 0.91; 95% CI, 0.82-1.01). CONCLUSIONS: Brief or extended periods of exposure to long-half-life benzodiazepines are associated with an increased risk of motor vehicle crash involvement in the elderly population. There is no such elevated risk for short-half-life benzodiazepines.

Accidents, Traffic↗
PubMed1997

High risk of breast carcinoma after irradiation of young women with Hodgkin's disease.

BACKGROUND: Treatment-associated second neoplasms have emerged as a major threat to the continued survival of patients cured of Hodgkin's disease. In this study, the authors investigated the risk of breast carcinoma in an irradiated Hodgkin's disease population. METHODS: One hundred and eleven women younger than 60 years presenting between 1964 and 1984 with Stage I and II Hodgkin's disease who received mantle irradiation were retrospectively analyzed and compared with an age specific population. Median follow-up was 18 years (range, 10-30 years), and the median age at initiation of therapy was 24 years. Kaplan-Meier actuarial risks, relative risks (RRs) (the ratio of the observed to the expected cases) with 95% confidence intervals (CIs), and the log rank test for trends were calculated. RESULTS: Fourteen women developed breast carcinoma: 8 of 33 patients younger than 20 years at the time of irradiation, 5 of 48 patients age 20 to 29 years, and 1 of 30 patients age 30 years or older. Actuarial calculation predicted a 34.0% (CI, 14.2-53.8) risk of breast carcinoma at 25 years after therapy for the youngest group, 22.3% (CI, 4.1-40.5) for the group of intermediate age, and 3.5% (CI, 0-10.1) for the oldest group. The RR of breast carcinoma was 56 (CI, 23.3-107) for those 19 years or younger at the time of treatment, 7.0 (CI, 2.3-16.4) for those age 20-29 years, and 0.9 (CI, 0-5.3) for those 30 years and older. Excluding 1 patient who was age 38 years at the time of irradiation, the remaining 13 breast carcinomas were tightly clustered in women irradiated between the ages of 14 through 25, and were detected in years 11 through 25 after treatment, with 7 occurring in years 15 through 18. CONCLUSIONS: Women younger than 30 years, particularly those younger than 20 years, who have received mantle irradiation for Hodgkin's disease require meticulous follow-up for breast carcinoma. The high incidence of breast carcinoma in this patient population should be considered when making treatment decisions in young women with early stage Hodgkin's disease.

Adolescent↗
PubMed1997

Inhaled and nasal glucocorticoids and the risks of ocular hypertension or open-angle glaucoma.

OBJECTIVE: To determine whether the use of inhaled and nasal glucocorticoids is associated with an increased risk of ocular hypertension or open-angle glaucoma. DESIGN: Case-control study. SETTING: Québec universal health insurance program for all elderly (registered in the Régie de l'assurance maladie du Québec [RAMQ] database). PATIENTS: Enrollees in the RAMQ database aged 66 years and older. The 9793 case patients were ophthalmology patients with a new diagnosis of borderline glaucoma or open-angle glaucoma or were newly started on treatment for ocular hypertension or glaucoma between 1988 and 1994. The 38,325 control patients were randomly selected among noncases with ophthalmologist visits in the same month and year as the case event (index date). MAIN OUTCOME MEASURES: The odds ratio (OR) of ocular hypertension or open-angle glaucoma was determined in patients using inhaled or nasal glucocorticoids relative to nonusers, using conditional logistic regression analysis. The OR was adjusted for age, sex, diabetes mellitus, systemic hypertension, use of ophthalmic and oral glucocorticoids, and characteristics of health care system use in the year before the index date. RESULTS: Overall, current use of inhaled and nasal glucocorticoids was not associated with an increased risk of ocular hypertension or open-angle glaucoma. Current users of high doses of inhaled steroids prescribed regularly for 3 or more months were at an increased risk with an OR of 1.44 (95% confidence interval, 1.01-2.06). CONCLUSION: Prolonged administration of high doses of inhaled glucocorticoids increases the risk of ocular hypertension or open-angle glaucoma. This finding suggests that in these patients intraocular pressure monitoring may be warranted.

Administration, Inhalation↗
PubMed1997

Ethnocultural predictors of postpartum infant-care behaviours among immigrants in Canada.

OBJECTIVES: To determine, among immigrants, what ethnocultural variables predict postpartum infant-care behaviours over and above other maternal and infant characteristics. METHODS: We recruited a cohort of immigrant women on hospital postpartum units. Data on predictor variables were collected during face-to-face interviews in the early postpartum period. Follow-up telephone interviews occurred at 3 months postpartum to assess infant-care behaviours. We identified 411 women meeting our eligibility criteria, of these 77.3% agreed to participate and 94% received follow-up interviews. RESULTS: In the first stage of a multiple linear regression analysis, maternal and infant predictors accounted for 24.2% of the variance in the 'Infant-Care Behaviours' score. In the second stage of model building, ethnocultural variables explained an additional 5.8% of the variance. Separate analyses for recent immigrants (resident in Canada less than 3 years) and less recent immigrants (3 or more years) yielded some differences in predictors. Among recent immigrants, worries about the infant's health, mother's education and an interaction term (current immigration status by parity) were significant predictors, explaining 23% of the variance. Among less recent immigrants, worries about the baby's health, prenatal class attendance, marital status and official language comprehension ability explained 37.7% of the variance. CONCLUSIONS: Our results indicate that assessing ethnocultural characteristics, in addition to maternal and infant characteristics, improves the prediction of 'Infant-Care Behaviours' scores.

Adolescent↗
PubMed1997

Measures of effect based on the sufficient causes model. 3. Multivariate analysis.

We discuss a method based on the sufficient causes model for estimating the causal and preventable fractions associated with any number of agents. P1, the cumulative risk of disease in the exposure category of interest, is given by the function: P1 = 1 - e-(i.+i1x1+...+ijxj+...+inxn)t. The presence or absence of sufficient cause in j in this exposure category is represented by x(j) (= 1.0), and parameter ij is the incidence density of completion of sufficient cause j. From ij, one can derive the risk difference and the causal and preventable fractions associated with sufficient cause j. The main assumptions required for these measures of effect to be unbiased are the constancy of incidence densities ij over time, the homogeneity of these densities over subjects, and the independence of occurrence times of sufficient causes within subjects. The estimation of the causal fraction requires all three assumptions. The preventable fraction requires only the homogeneity assumption. The risk difference requires none of these assumptions. This causal model probably applies to very few real situations, but it can serve as an epidemiologically meaningful starting point for the development of models adapted to particular situations whose underlying causal processes are known or can be hypothesized.

Epidemiologic Methods↗
PubMed1997

Risk of spontaneous abortion in women occupationally exposed to anaesthetic gases: a meta-analysis.

OBJECTIVES: To determine the association between maternal occupational exposure to anaesthetic gases and risk of spontaneous abortion. METHODS: A meta-analysis was performed of published epidemiological studies identified from literature reviews, unsystematic perusal of reference lists of relevant publications, and two Medline searches (1984-92, keywords: anaesthetic gases; anaesthetics; anaesthetics, local; operating rooms; operating room nursing; pregnancy; abortion; 1985-92, keywords: anaesthetics; adverse effects; occupational exposure; anaesthesia, inhalation; operating room nursing; pregnancy; abortion). All peer reviewed studies were retained. Student theses were excluded, as were conference abstracts, unpublished material, and two studies in which data on paternal and maternal occupational exposures were pooled. The relative risk of spontaneous abortion was estimated. RESULTS: One study found no increase in risk of abortion when gases were scavenged or when the exposure to unscavenged gases was low. None of the studies included ambient gas sampling. 24 comparisons between exposed and unexposed women, obtained from 19 reports, were included. The overall relative risk was 1.48 (95% confidence interval (95% CI), 1.4 to 1.58). To test whether this result was influenced by the quality of the studies, the validity of the reviewed papers was rated on the basis of three criteria: appropriateness of the unexposed comparison group, control for non-occupational confounding variables, and response rate. The estimate of risk increased to 1.9 (95% CI, 1.72 to 2.09) when analysis was restricted to the six comparisons which were rated the most rigorous. CONCLUSIONS: Epidemiological studies based on data obtained in the prescavenging era indicate an increased risk of spontaneous abortion. The estimated increased risk was not diminished but rather increased by exclusion of the more methodologically flawed studies.

Abortion, Spontaneous↗
PubMed1996

Cost effectiveness of screening for primary open angle glaucoma.

OBJECTIVES AND SETTING: To determine the cost effectiveness of screening for glaucoma. METHODS: Information on treatment efficacy, diagnostic methods, epidemiological characteristics of glaucoma, and costs were determined from the literature, from administrative databases, and from experts. Scenarios with different screening frequency, age, participation in screening, compliance with treatment, treatment efficacy, and diagnostic tests were examined. RESULTS: The initial scenario comprised three-yearly screening of subjects aged 40-79 by funduscopy and tonometry, followed by perimetry when abnormalities were discovered. The assumption of levels of participation in screening and of compliance with treatment of 75%, and treatment efficacy of 50% resulted in a cost of $C100,000 per year of blindness prevented. A scenario in which screening was restricted to subjects aged 65-79, with the same input variables, would prevent 81% of the cases of blindness prevented with scenario 1, at a cost of $C42,000 per year of blindness prevented. Screening with tonometry only as the initial diagnostic test in subjects aged 65-79 would result in a cost of $C36,000 per year of blindness prevented, but would only prevent 59% of the cases prevented with scenario 1. CONCLUSIONS: There is as yet no proof that treatment of glaucoma or of high intraocular pressure will arrest the progression of glaucoma to blindness. Even when treatment efficacy is assumed to be as high as 50%, however, the cost effectiveness of most glaucoma screening programmes considered would not be competitive.

Adult↗
PubMed1995

Incidence of second cancers in patients treated for Hodgkin's disease.

BACKGROUND: Numerous studies of treatment for Hodgkin's disease have demonstrated large increases in the incidence of leukemia in the early years following chemotherapy, although the duration of effect and the specific agents involved are not well understood. Also, some, but not all, studies have indicated that the incidence of certain solid tumors increases following treatment for Hodgkin's disease. PURPOSE: We studied the association between treatment for Hodgkin's disease and the incidence of second cancers. METHODS: We conducted a study within a cohort that included 10,472 patients from 14 cancer centers in the United States and Canada who were first diagnosed as having Hodgkin's disease at some point from 1940 through 1987. Discounting the 1st year after diagnosis, the average length of follow-up was 7.1 years per subject. RESULTS: We observed 122 leukemias and 438 solid tumors. The relative risk (RR) of leukemia following chemotherapy, compared with no chemotherapy, was 14 (95% confidence interval [CI] = 5.6-35). Increased risks of leukemia were observed after treatment with chlorambucil (RR = 2.0; 95% CI = 1.1-3.6), procarbazine (RR = 4.9; 95% CI = 2.6-9.1), vinblastine (RR = 1.7; 95% CI = 1.1-2.8), and a group of rarely used drugs that included methotrexate, vindesine, etoposide, and 22 others (RR = 3.8; 95% CI = 1.9-7.4). RRs were also estimated for various combinations of drugs, including MOPP (mechlorethamine, vincristine, procarbazine, and prednisone) (RR = 5.9; 95% CI = 2.9-12) and ABVD (doxorubicin, bleomycin, vinblastine, and dacarbazine) (RR = 1.5; 95% CI = 0.7-3.4). The RR of leukemia associated with splenectomy was 1.6 (95% CI = 1.0-2.5). The RR of solid tumors following chemotherapy was 1.4 (95% CI = 1.1-1.8). For the group of rarely used drugs, the RR of solid tumors was 3.1 (95% CI = 1.7-5.8). Chemotherapy was associated with an increased risk of cancers of the bones, joints, articular cartilage, and soft tissues (RR = 6.0; 95% CI = 1.7-20), and cancers of the female genital system (RR = 1.8; 95% CI = 1.1-3.2). In patients followed for 10 or more years after radiotherapy, increased risks were found for cancers of the respiratory system and intrathoracic organs (RR = 2.7; 95% CI = 1.1-6.8) and for cancers of the female genital system (RR = 2.4; 95% CI = 1.1-5.4). CONCLUSIONS: Procarbazine, chlorambucil, and vinblastine are associated with increased leukemia risk. Combination drug regimens have leukemogenic effects estimated as the product of RRs for individual drugs. Chemotherapy and radiotherapy increase the risk of selected solid tumors, and the effect of chemotherapy on solid tumor risk is weaker than the leukemogenic effect. IMPLICATIONS: Without doubt, the benefits of treatment of Hodgkin's disease outweigh the risk of a subsequent malignancy, but data on the carcinogenic effects of radiation and drugs beyond 10 years after treatment continue to be sparse, and future analyses should be directed at long-term survivors.

Adolescent↗
PubMed1994

Spouse similarity for psychological distress and well-being: a population study.

While spouse similarity for psychiatric morbidity has been the object of numerous studies, most of these focused on clinical samples and, consequently, the interpretation of their results is limited by the existence of a selection bias. In this study, conducted on a sample of 845 general population couples, significant spouse similarity was observed for psychological distress and well-being, characterized by a marked symmetry in the relation between spouses' scores. The sex differences observed in many earlier studies would appear essentially to be artefactual. Spouse similarity was also found to be significant in the subpopulation of couples married less than two years, which pointed to assortative mating for psychological distress and well-being. While many studies have found educational dissimilarity and age difference between spouses to be associated with certain health variables, such as high blood pressure and coronary heart disease, these variables do not have a significant influence on individual levels of psychological distress and well-being. Spouse similarity for socio-demographic characteristics does not play a significant role in explaining spouse similarity for mental health. Consequently, assortative mating for psychological distress and well-being would appear to be primarily due to personal preference.

Adaptation, Psychological↗