Risk factors for falling among community-dwelling seniors using home-care services: An extended hazards model with time-dependent covariates and multiple events

The identification of risk factors for falls in longitudinal studies becomes difficult because of exposures that change during the follow-up and also because individual subjects may experience an event more than once. These issues have been neglected and improper statistical techniques have been used. The typical approaches have been to report the proportion of fallers or the time to first fall. Both avoid the underlying assumption of independence between events and discard pertinent data. We review the existing methods and propose a Cox hazards extension. We exemplify it in the study of potential risk factors associated with all falls in 959 seniors. Finally, we compare the results of the proposed Wei, Lin, & Weissfeld (WLW) method with those of several other techniques. Stable exposure variables measured at baseline and updated time-varying exposures include socio-demographic characteristics, BMI, nutritional risk, alcohol consumption, home hazards, gait and balance, and medications. Results demonstrate that the usual methods of analyzing risk factors for falling are inappropriate, as they produce considerable biases relative to the WLW model using time-dependent covariates. Results also show that modeling for first events may be inefficient, given that the risk of occurrence varies between falls.

Risk factors for falling among community-dwelling seniors using home-care services: an extended hazards model with time-dependent covariates and multiple events

The identification of risk factors for falls in longitudinal studies becomes difficult because of exposures that change during the follow-up and also because individual subjects may experience an event more than once. These issues have been neglected and improper statistical techniques have been used. The typical approaches have been to report the proportion of fallers or the time to first fall. Both avoid the underlying assumption of independence between events and discard pertinent data. We review the existing methods and propose a Cox hazards extension. We exemplify it in the study of potential risk factors associated with all falls in 959 seniors. Finally, we compare the results of the proposed Wei, Lin, & Weissfeld (WLW) method with those of several other techniques. Stable exposure variables measured at baseline and updated time-varying exposures include socio-demographic characteristics, BMI, nutritional risk, alcohol consumption, home hazards, gait and balance, and medications. Results demonstrate that the usual methods of analyzing risk factors for falling are inappropriate, as they produce considerable biases relative to the WLW model using time-dependent covariates. Results also show that modeling for first events may be inefficient, given that the risk of occurrence varies between falls.

[The Edinburgh Postnatal Depression Scale: the validity of its Quebec version for a population low socioeconomic status mothers]

This paper investigates the construct validity and reliability of a Quebec version of the Edinburgh Postnatal Depression Scale (EPDS) for a population of low-socioeconomic-status mothers. This scale was constructed for the specific purpose of measuring mothers' symptoms of depression during the postnatal period in an effort to alleviate the validity problems that could arise from depression scales intended for the general population. Two hundred and twenty-four mothers participating in a Quebec prevention program, "Naître égaux, grandir en santé" (Martin & Boyer, 1995) filled out the EPDS between the 22nd and the 35th day postpartum. A confirmatory factor analysis, conducted with LISREL, gives a 2-factor structure for the EPDS, the first representing symptoms of depression and the second symptoms of anxiety. This structure differs from the one presented by Cox, Holden, and Sagovsky (1987), authors of the EPDS. It corresponds, however to the results of other authors who looked at the EPDS with confirmatory factor analysis (Pop, Komproe, & van Son, 1992) and indicates a good construct validity. The reliability of the scale also appears satisfactory, with a Cronbach alpha co-efficient of 0.82.

Development of a systematic observation protocol of physical exposure of the back: a preliminary study

OBJECTIVE

At present there is no systematic observation protocol for the assessment of the multi-factorial aspects of physical exposure related to the back used within the constraints of occupational epidemiological research. In this context, a new preliminary systematic observation protocol is proposed to assess exposure to physical loading of the back using nine categories of physical risk factors: the SOPE back protocol. The objective of this study was to investigate whether the new protocol can correctly identify the level of exposure related to measured physical loading of the back.

METHODS

The subjects of this closed cohort study were 451 manual workers at a natural gas distribution company. The assessment of exposure was made with the protocol using groups with different job titles. The workers were followed for a 2 yr period to establish the risk of a new occurrence of complete disability related to the back (NOCD back injury) in each job grouping.

RESULTS

Based on the median of the total scores derived from the protocol, two levels of exposure were identified (high and low).

CONCLUSION

Taking into account the limitations of this study, the protocol in development may be a good tool to establish two levels of exposure to physical loading of the back in large epidemiological studies of occupational low back pain. Further research is needed to replicate these results with larger samples and to test the reliability and predictive validity of the protocol.

Socio-economic disparities in preterm birth: causal pathways and mechanisms

Preterm birth is the leading cause of infant mortality in industrialised societies. Its incidence is greatly increased among the socially disadvantaged, but the reasons for this excess are unclear and have been relatively unexplored. We hypothesise two distinct sets of causal pathways and mechanisms that may explain social disparities in preterm birth. The first set involves chronic and acute psychosocial stressors, psychological distress caused by those stressors, increased secretion of placental corticotropin releasing hormone (CRH), changes in sexual behaviours or enhanced susceptibility to bacterial vaginosis and chorioamnionitis, cigarette smoking or cocaine use, and decidual vasculopathy. The second hypothesised pathway is a gene-environment interaction based on a highly prevalent mutation in the gene for methylenetetrahydrofolate reductase (MTHFR), combined with low folate intake from the diet and from prenatal vitamin supplements, consequent hyperhomocysteinemia, and decidual vasculopathy. We propose to test these hypothesised pathways and mechanisms in a nested case-control study within a prospectively recruited and followed cohort of pregnant women with singleton pregnancies who deliver at one of four Montreal hospitals that serve an ethnically and socio-economically diverse population. Following recruitment during the late first or early second trimester, participating women are seen at 24-26 weeks, when a research nurse obtains a detailed medical and obstetric history; administers several scales to assess chronic and acute stressors and psychological function; obtains blood samples for CRH, red blood cell and plasma folate, homocysteine, and DNA for the MTHFR mutation; and performs a digital and speculum examination to measure cervical length and vaginal pH and to obtain swabs for bacterial vaginosis and fetal fibronectin. After delivery, each case (delivery at < 37 completed weeks following spontaneous onset of labour or prelabour rupture of membranes) and two controls are selected for placental pathological examination, hair analysis of cotinine, cocaine, and benzoylecgonine, and analysis of stored blood and vaginal specimens. Statistical analysis will be based on multiple logistic regression and structural equation modelling, with sequential construction of models of potential aetiological determinants and covariates to test the hypothesised causal pathways and mechanisms. The research we propose should improve understanding of the factors and processes that mediate social disparities in preterm birth. This improved understanding should help not only in developing strategies to reduce the disparities but also in suggesting preventive interventions applicable across the entire socio-economic spectrum.

Socio-economic disparities in pregnancy outcome: why do the poor fare so poorly?

In this paper, we review the evidence bearing on socio-economic disparities in pregnancy outcome, focusing on aetiological factors mediating the disparities in intrauterine growth restriction (IUGR) and preterm birth. We first summarise what is known about the attributable determinants of IUGR and preterm birth, emphasising their quantitative contributions (aetiological fractions) from a public health perspective. We then review studies relating these determinants to socio-economic status and, combined with the evidence about their aetiological fractions, reach some tentative conclusions about their roles as mediators of the socio-economic disparities. Cigarette smoking during pregnancy appears to be the most important mediating factor for IUGR, with low gestational weight gain and short stature also playing substantial roles. For preterm birth, socio-economic gradients in bacterial vaginosis and cigarette smoking appear to explain some of the socio-economic disparities; psychosocial factors may prove even more important, but their aetiological links with preterm birth require further clarification. Research that identifies and quantifies the causal pathways and mechanisms whereby social disadvantage leads to higher risks of IUGR and preterm birth may eventually help to reduce current disparities and improve pregnancy outcome across the entire socio-economic spectrum.

Occupational disability related to back pain: application of a theoretical model of work disability using prospective cohorts of manual workers

BACKGROUND

A new model of work disability was developed based on the assumption that four different groups of workers are present at the beginning of a prospective epidemiologic study: one group of workers without back pain, and three groups of workers with back pain and a gradient of work disability. The goal of this research was to verify if these groups comprise workers at different levels of risk of occurrence of complete work disability related to back injury.

METHODS

Prospective cohorts of manual workers (n=578) were followed for 1 year to document the risk of occurrence of complete disability related to back injury.

RESULTS

The results showed that the workers who presented with back pain without work disability at the beginning of the study were at less risk compared to all the other workers in the cohort. Moreover, an effect modification was found between the workers who initially presented with back pain without work disability and a past history of compensation for back injury, adding credence to the non-similarity of these workers to the others.

CONCLUSIONS

Based on these results, further studies should focus on improving the knowledge of the characteristics of these workers leading to a better understanding of how to prevent occupational low-back pain.

Application of a non-indexed dual sprayer pneumatically assisted electrospray source to the high throughput quantitation of target compounds in biological fluids

The need for increased throughput in the quantitation of target compounds in biological fluids by high performance liquid chromatography/mass spectrometry continues to drive research in this area. This report describes the application of a prototype dual sprayer electrospray source for the quantitative analysis of biological samples. Quantitative performance for 180 compounds in a microsomal stability assay was found to be adequate when compared with a conventional single sprayer measurement. Issues with use of dual sprayers in a routine production environment are discussed.

Results of a lead decontamination program

An epidemiological survey was conducted in August 1991 to evaluate the impact of a public health program. The objective of the program was to decrease the level of exposure to lead of children who lived within 200 m of a lead- reclamation plant. In 1989, these children had a geometric mean blood lead level of 9.2 micrograms/dl (0.44 mu mol/l). Children who were 6 mo to 10 y of age (N = 101) participated in the survey. Demographic and behavioral characteristics of the children and their parents were ascertained by interviewers. Blood samples were taken by venipuncture. Geometric mean blood levels were calculated by age in 1991 and by residence in 1989. In 1991, the geometric mean blood lead level had decreased to 5.0 micrograms/dl (0.24 mu mol/l) in children. There was no difference in mean blood lead levels with respect to age or residence. From 1989 to 1991, a significant decrease in the proportion of children who engaged in hand-to-mouth activities was also observed. The lead-poisoning prevention program reached its main objective stated above. The success of this program was attributed to the coordinated actions of public agencies at both the provincial and local levels.

Incidence of cancer among persons living near a municipal solid waste landfill site in Montreal, Québec

The Miron Quarry municipal solid waste landfill site in Montreal, Québec, generates copious quantities of methane and other gases, including a rich mixture of volatile organic compounds, some of which are recognized or suspected human carcinogens. The site is the third largest in North America and is located in the center of a densely populated area. Using data from the Québec Tumour Registry, we conducted Poisson regression analyses to evaluate whether cancer incidence among persons who lived near the site was higher than expected. Potential exposure to ambient air pollutants from the site was defined in terms of a set of geographic exposure zones proximal to the site. A set of reference areas distal from the site was selected to be similar to these exposure zones with respect to several key sociodemographic factors. Risk ratios (RRs) were adjusted for age and calendar year. Among men living in the exposure zone closest to the site, elevated risks were observed for cancers of the stomach (RR = 1.3, 95% confidence interval [95% CI] = 1.0-1.5); liver and intrahepatic bile ducts (RR = 1.3, 95% CI = 0.9-1.8); and trachea, bronchus, and lung (RR = 1.1, 95% CI = 1.0-1.2). Among women, rates of stomach cancer (RR = 1.2; 95% CI = 0.9-1.5) and cervix uteri cancer were elevated (RR = 1.2, 95% CI = 1.0-1.5), but breast cancer incidence was less than expected (RR = 0.9, 95% CI = 0.9-1.0). Prostate cancer was also elevated in one of the proximal exposure subzones (RR = 1.2, 95% CI = 1.0-1.4). Further studies at this and at other landfill sites are needed to confirm or refute these observations.

Low birth weight and preterm births among infants born to women living near a municipal solid waste landfill site in Montreal, Quebec

Using data from the Quebec birth registration file, case-control analyses were conducted in order to evaluate the risk of low birth weight (< 2500 g), very low birth weight (< 1500 g), preterm birth (< 37 completed weeks), and small for gestational age (< third percentile) among infants born to women living near a municipal solid waste landfill site in a densely populated area of Montreal, Quebec. Potential exposure to vapors and gases (biogas) was defined in terms of exposure zones around the site. A set of reference areas was selected to be similar to these exposure zones on a number of key sociodemographic factors. Odds ratios (OR) adjusted for variables on the birth file were calculated using logistic regression. Low birth weight was significantly elevated in the exposure zone proximal to the site (adjusted OR = 1.20; 1107 exposed cases; 95% confidence interval: 1.04-1.39). Excess risks were also observed for small for gestational age, but the association was not as strong as for low birth weight (adjusted OR = 1.09; 951 exposed cases; 95% confidence interval: 0.96-1.24). No significant positive associations were observed for very low birth weight or for preterm birth. Because it was not possible to evaluate the effects of all potentially important confounding factors and because detailed environmental exposure assessments were not available, it is not possible to conclude definitively whether low birth weight and small for gestational age are associated with exposure to biogas. Further studies at this and at other landfill sites are warranted in order to confirm or refute these observations and to investigate other possible adverse reproductive outcomes.

Blood lead levels in children and pregnant women living near a lead-reclamation plant

OBJECTIVE

To determine the effect of lead contamination around a lead-reclamation plant on the blood lead levels of children and pregnant women living in the area.

DESIGN

Prevalence study.

SETTING

Residents living 150 m or less (high-exposure area), 151 to 400 m (intermediate-exposure area) or 401 to 800 m (low-exposure area) southeast from the plant.

PARTICIPANTS

All children aged 10 years or less and all pregnant women living in the designated area.

OUTCOME MEASURES

Correlation of venous blood lead levels with soil lead concentrations in the areas in which the subjects lived and with sociodemographic and behavioural factors.

MAIN RESULTS

Of the estimated 57 pregnant women 38 (67%) participated: 20 were in the high-exposure area and 18 in the other two areas; their geometric mean blood lead levels were low (0.15 and 0.13 mumol/L respectively). Of the 625 eligible children 510 (82%) participated: 169 were in the high-exposure area, 179 in the intermediate-exposure area and 162 in the low-exposure area; their geometric mean lead levels were 0.43, 0.30 and 0.26 mumol/L respectively. Within each age group children in the high-exposure area had the highest levels. The mean levels for children aged 6 months to 5 years were 0.49, 0.35 and 0.28 mumol/L in the three areas respectively. Within each exposure group children aged 1 to 2 years had the highest levels. No potential confounding variables could explain the relation between blood lead level and soil lead concentration.

CONCLUSIONS

The pregnant women's blood lead levels did not seem to be affected by exposure level, but the children's levels were primarily related to the soil lead concentration.

Stillbirth and chemical exposure of pregnant workers

A case-referent study was conducted among women in health, personal services, agriculture, and manufacturing industries. Stillbirths (N = 227) were matched with live births (N = 227) on mother's age, gravidity, and socioeconomic status. Exposure was assessed by workplace visits, telephone calls, or estimations. Conditional logistic regression analyses were used which controlled for maternal education, race, cigarette and alcohol consumption, and previous stillbirths. The results showed a significant decreased risk of stillbirth for hairdressers [odds ratio (OR) 0.1, 95% confidence interval (95% CI) 0.0-0.3)) and garment workers (OR 0.2, 95% CI 0.1-0.8)). Women in metal-electrical-chemical industries (OR 5.1, 95% CI 1.0-26.4] and those with low-level exposure to pesticides or germicides (OR 3.1, 95% CI 1.1-8.6) had an increased risk. Ergonomic factors could be related to some of these findings.

Suicidal behavior among inner-city Hispanic adolescent females

Suicidal behavior is disproportionately frequent among inner-city Hispanic adolescent girls. In an attempt to generate a multifactorial set of hypotheses to explain this behavior, 33 such subjects consecutively admitted for suicidal behavior and 15 demographically identical nonsuicidal subjects were assessed by means of a structured interview. Mothers of all subjects were also assessed. Attempts were nearly always impulsive and nonlethal, though often with a stated wish to die. Nearly all were overdoses, and were precipitated by conflicts with mother or boyfriend. Mothers could usually identify the precipitants. Attempters' parents were less often born in the U.S., their mothers seemed medically less healthy, and their extended families were more often supported by public assistance, and had a higher incidence of criminal and psychiatric problems. School performance was poorer among attempters, who had suffered more and earlier losses, especially of biologic fathers, with whom fewer had ongoing relationships. They more often had boyfriends, had begun sexual activity, had recently lost friends, and expressed a mistrustful stance toward friendships. Similarly, their mothers had fewer friends and more often expressed a mistrustful stance. Relationships with mothers seemed more intense, desperate, and even violent, and attempters were much more often parentified, i.e., mothering their mothers. Although both groups often assumed caretaking roles in their families, attempters were more negatively described by themselves and by their mothers. While knowledge of suicidal models was common in both groups, attempters' mothers knew of even more models than did their daughters or the nonsuicidal subjects or their mothers. Notably, more attempters' mothers had themselves made attempts. Families of most attempters were usually mobilized by the attempt. These findings permit the construction of a putative profile of risk factors that can be tested more rigorously.

Association between spontaneous abortion and ergonomic factors. A literature review of the epidemiologic evidence

This article presents a literature review of seven epidemiologic studies which address the issue of spontaneous abortion and ergonomic factors. The following four ergonomic factors are analyzed: (i) shift work, (ii) piece work, (iii) posture, (iv) heavy lifting and physical effort. Among these factors, the last, heavy lifting and physical effort, is the only one that seems to be associated with an increased risk of spontaneous abortion.

A mortality study of oil refinery workers

Survival status of 1205 men employed for more than five years in a Canadian oil refinery in East Montreal, from 1928 through 1976, was assessed and death certificates were reviewed. Expected numbers of deaths were estimated based upon age- and cause-specific death rates for the Province of Quebec applied to person-years at work. Oil refinery workers showed a standard mortality ratio lower than expected for all causes of death (SMR = 78.43). Three cancers of the brain were found among young people who died less than 20 years since start of exposure. This was statistically higher than expected. Cancers of the digestive system, though not significantly higher than expected, remained suspect of being associated with work. There is a need to expand this research to other oil refinery workers.