The use of cost-utility analysis for the evaluation of caries prevention: an exploratory case study of two community-based public health interventions in a high-risk population in the UK

BACKGROUND

Economic evaluations are important tools for decision makers to determine the best allocation of resources in a healthcare system. This study explored the use of economic evaluation in oral health promotion.

METHODS

A literature review identified oral health promotion programmes that measured both the health impact and costs of oral health interventions. A decision analysis model was constructed to examine the cost utility of preventing dental caries in 5 and 12-year-old children via tooth brushing schemes and fluoride varnish programmes. The costs per child that would be justified according to the National Institute for Health and Care Excellence's threshold of £20,000 per QALY were calculated.

RESULTS

The analysis showed that NICE would consider that the expenditure of £55 per child on supervised tooth brushing, or £100 per child on fluoride varnish application would give sufficient health benefits to be justified according to their threshold.

CONCLUSIONS

Greater attention needs to be paid to the collection of robust data on costs for oral health promotion. Dental researchers also urgently need to collect outcome data in a form that can be translated into a Quality of Life measure, so that the true cost effectiveness and value for money achieved through the prevention of dental disease can be recognised and compared to other allocations of resource.

Committee on air pollution effects research: 40 years of UK air pollution

The UK Committee on Air Pollution Effects Research (CAPER) was established 40 years ago. This special section was compiled to mark this anniversary. During this time there have been dramatic changes in the composition of the air over the UK. The four papers in this special section of Environmental Pollution represent the current air pollution effects research focus on ozone and nitrogen deposition, two related issues and are proving from a policy perspective to be quite intractable issues. The UK CAPER research community continues to advance the underpinning science and engages closely with the user community in government departments.

Impact of preferential sampling on exposure prediction and health effect inference in the context of air pollution epidemiology

Preferential sampling has been defined in the context of geostatistical modeling as the dependence between the sampling locations and the process that describes the spatial structure of the data. It can occur when networks are designed to find high values. For example, in networks based on the U.S. Clean Air Act monitors are sited to determine whether air quality standards are exceeded. We study the impact of the design of monitor networks in the context of air pollution epidemiology studies. The effect of preferential sampling has been illustrated in the literature by highlighting its impact on spatial predictions. In this paper, we use these predictions as input in a second stage analysis, and we assess how they affect health effect inference. Our work is motivated by data from two United States regulatory networks and health data from the Multi-Ethnic Study of Atherosclerosis and Air Pollution. The two networks were designed to monitor air pollution in urban and rural areas respectively, and we found that the health analysis results based on the two networks can lead to different scientific conclusions. We use preferential sampling to gain insight into these differences. We designed a simulation study, and found that the validity and reliability of the health effect estimate can be greatly affected by how we sample the monitor locations. To better understand its effect on second stage inference, we identify two components of preferential sampling that shed light on how preferential sampling alters the properties of the health effect estimate.

Ammonium as a driving force of plant diversity and ecosystem functioning: observations based on 5 years' manipulation of N dose and form in a Mediterranean ecosystem

Enhanced nitrogen (N) availability is one of the main drivers of biodiversity loss and degradation of ecosystem functions. However, in very nutrient-poor ecosystems, enhanced N input can, in the short-term, promote diversity. Mediterranean Basin ecosystems are nutrient-limited biodiversity hotspots, but no information is available on their medium- or long-term responses to enhanced N input. Since 2007, we have been manipulating the form and dose of available N in a Mediterranean Basin maquis in south-western Europe that has low ambient N deposition (<4 kg N ha⁻¹ yr⁻¹) and low soil N content (0.1%). N availability was modified by the addition of 40 kg N ha⁻¹ yr⁻¹ as a 1∶1 NH₄Cl to (NH₄)₂SO₄ mixture, and 40 and 80 kg N ha⁻¹ yr⁻¹ as NH₄NO₃. Over the following 5 years, the impacts on plant composition and diversity (richness and evenness) and some ecosystem characteristics (soil extractable N and organic matter, aboveground biomass and % of bare soil) were assessed. Plant species richness increased with enhanced N input and was more related to ammonium than to nitrate. Exposure to 40 kg NH₄⁺-N ha⁻¹ yr⁻¹ (alone and with nitrate) enhanced plant richness, but did not increase aboveground biomass; soil extractable N even increased under 80 kg NH₄NO₃-N ha⁻¹ yr⁻¹ and the % of bare soil increased under 40 kg NH₄⁺-N ha⁻¹ yr⁻¹. The treatment containing less ammonium, 40 kg NH₄NO₃-N ha⁻¹ yr⁻¹, did not enhance plant diversity but promoted aboveground biomass and reduced the % of bare soil. Data suggest that enhanced NH_y availability affects the structure of the maquis, which may promote soil erosion and N leakage, whereas enhanced NO_x availability leads to biomass accumulation which may increase the fire risk. These observations are relevant for land use management in biodiverse and fragmented ecosystems such as the maquis, especially in conservation areas.

Residential indoor PM2.5 in wood stove homes: follow-up of the Libby changeout program

In 2005 through 2008, a small rural mountain valley community engaged in a woodstove changeout program to address concerns of poor ambient air quality. During this program, we assessed changes to indoor air quality before and after the introduction of a new, lower emission woodstove. We previously reported a >70% reduction in indoor PM(2.5) concentrations in homes following the installation of a new Environmental Protection Agency's-certified stove within the home. We report here on follow-up of the experiences in these and other homes over three winters of sample collection. In 21 homes, we compared pre-changeout PM(2.5) concentrations [mean (s.d.) = 45.0 (33.0) μg/m(3)] to multiple post-changeout measures of PM(2.5) concentrations using a DustTrak. The mean reduction (and 95% confidence interval) from pre-changeout to post-changeout was -18.5 μg/m(3) (-31.9, -5.2), adjusting for ambient PM(2.5) , ambient temperature, and other factors. Findings across homes and across years were highly variable, and a subset of homes did not experience a reduction in PM(2.5) following changeout. Reductions were also observed for organic carbon, elemental carbon, and levoglucosan, but increases were observed for dehydroabietic acid and abietic acid. Despite overall improvements in indoor air quality, the varied response across homes may be due to factors other than the introduction of a new woodstove.

PRACTICAL IMPLICATIONS

Biomass combustion is a common source of ambient PM(2.5) in many cold-climate communities. The replacement of older model woodstoves with newer technology woodstoves is a potential intervention strategy to improve air quality in these communities. In addition to ambient air, woodstove changeouts should improve residential indoor air quality. We present results from a multi-winter study to evaluate the efficacy of woodstove changeouts on improving indoor air quality. Reductions in indoor PM(2.5) were evident, but this observation was not consistent across all homes. These findings suggest that other factors beyond the introduction of an improved wood burning device are relevant to improving indoor air quality in wood burning homes.

Evaluation and comparison of three exposure assessment techniques

This study was conducted to verify the performance of a recently developed subjective rating (SR) exposure assessment technique and to compare estimates made using this and two other techniques (trade mean, or TM, and task-based, or TB, approaches) to measured exposures. Subjects (n = 68) each completed three full-shift noise measurements over 4 months. Individual measured mean exposures were created by averaging each subject's repeated measurements, and TM, TB, and SR estimates were created using noise levels from worksites external to the current study. The bias, precision, accuracy, and absolute agreement of estimates created using the three techniques were evaluated by comparing estimated exposures with measured exposures. Trade mean estimates showed little bias, while neither the TM nor the SR techniques produced unbiased estimates, and the SR estimates showed the greatest bias of the three techniques. Accuracy was essentially equivalent among the three techniques. All three techniques showed poor agreement with measured exposures and were not highly correlated with each other. Estimates from the SR technique generally performed similarly to the TM and TB techniques. Methods to incorporate information from each technique into exposure estimates should be explored.

The Denver Aerosol Sources and Health (DASH) Study: Overview and Early Findings

Improved understanding of the sources of air pollution that are most harmful could aid in developing more effective measures for protecting human health. The Denver Aerosol Sources and Health (DASH) study was designed to identify the sources of ambient fine particulate matter (PM(2.5)) that are most responsible for the adverse health effects of short-term exposure to PM (2.5). Daily 24-hour PM(2.5) sampling began in July 2002 at a residential monitoring site in Denver, Colorado, using both Teflon and quartz filter samplers. Sampling is planned to continue through 2008. Chemical speciation is being carried out for mass, inorganic ionic compounds (sulfate, nitrate and ammonium), and carbonaceous components, including elemental carbon, organic carbon, temperature-resolved organic carbon fractions and a large array of organic compounds. In addition, water soluble metals were measured daily for 12 months in 2003. A receptor-based source apportionment approach utilizing positive matrix factorization (PMF) will be used to identify PM (2.5) source contributions for each 24-hour period. Based on a preliminary assessment using synthetic data, the proposed source apportionment should be able to identify many important sources on a daily basis, including secondary ammonium nitrate and ammonium sulfate, diesel vehicle exhaust, road dust, wood combustion and vegetative debris. Meat cooking, gasoline vehicle exhaust and natural gas combustion were more challenging for PMF to accurately identify due to high detection limits for certain organic molecular marker compounds. Measurements of these compounds are being improved and supplemented with additional organic molecular marker compounds. The health study will investigate associations between daily source contributions and an array of health endpoints, including daily mortality and hospitalizations and measures of asthma control in asthmatic children. Findings from the DASH study, in addition to being of interest to policymakers, by identifying harmful PM(2.5) sources may provide insights into mechanisms of PM effect.

The interpretation of exposure effect estimates in chronic air pollution studies

In this article we consider the interpretation of regression parameters used to represent 'chronic' or 'long-term' air pollution exposure effects. Although scientific interest typically lies in understanding such effects at the level of the individual, studies have generally employed a semi-ecological design; outcomes and confounder information are collected on individuals while exposure is only available at the aggregate-or group-level. A precise interpretation of results from a semi-ecological design must take into account the aggregated nature, both spatial and temporal, of the exposure measure. The most common analysis approach for assessing chronic exposure effects has been within the Cox proportional hazards model framework; specific analyses are tailored to accommodate the shortcomings of the available exposure information. We revisit the underlying assumptions of the Cox model and discuss the implications of two common aspects of chronic effects studies: time-dependent exposures and time-varying effects. Focusing on the consequences of temporal aggregation of exposure, we show that an estimate obtained from a time-aggregated semi-ecological design can correspond to very different underlying time-varying exposure and risk scenarios. Further, distinguishing which of these is correct is not possible from the semi-ecological data alone. Our goal is to highlight some statistical issues faced by existing studies of chronic air pollution effects, and aid in the development and planning of future studies.

'Building a new normality': mothers' experiences of caring for a child with acute lymphoblastic leukaemia

BACKGROUND

Treatment of childhood cancer occurs over a 2- to 3-year period, with initial intense phases of chemotherapy followed by less severe treatment periods. From first diagnosis, families are encouraged by healthcare professionals (following government guidelines) to try to maintain a normal life. The aim of this paper is to contribute to our understanding of how 'normal' family life is compromised from the perspective of the families themselves during this period of extreme stress and concern for the health and well-being of their child.

METHODS

This study was longitudinal and involved a cross section of 32 mothers of children recently diagnosed with acute lymphoblastic leukaemia (ALL) currently participating in the Medical Research Council ALL-97 randomized control trial. Mothers were interviewed at three time points (3-4 months post diagnosis, 15 and 27 months) using a semi-structured format with open-ended questions. A qualitative methodology was employed to analyse interview data using Thematic analysis.

RESULTS

Mothers reported understanding the importance of achieving normal life, but described how this was difficult to realize. At first interview, mothers were optimistic that they could achieve the 'normal life' as advised by healthcare workers. At 12 and 24 months, although all mothers reported that life was not back to normal, there were differences in how they perceived this lack of normality. Whereas some families experienced frustration and disappointment, others had adjusted and managed to accept the new order.

CONCLUSIONS

Families felt encouraged on diagnosis to be told that despite the severity of the disease and treatment regime, a normal life was possible and should be pursued. Our findings indicate that over time, more concrete information is needed to guide parents through the treatment process in order to help them achieve this.

Diagnostic indicators of elevated nitrogen deposition

Tissue N content of mosses, which has been shown to be an indicator of enhanced N, was studied at a range of locations dominated either by wet or dry deposited and oxidised and reduced forms of N. Tissue N responded differently to wet and dry deposited N. For a 1 kg ha(-1) y(-1) increase in N deposition, tissue N increased by 0.01% at wet deposition sites but by 0.03% at sites dominated by dry deposited NH3. Tissue N at wet deposition sites responded more to concentrations of NO3- and NH4+ in precipitation (r(2) 0.63) than to total N deposition (r(2) 0.27), concentration explaining 66% of the variation in tissue N, wet deposition 33%. The study clearly concludes that tissue N concentration in mosses provides a good indication of N deposition at sites where deposition is dominated by NH3, and is also valuable in identifying vegetation exposed to large concentrations of NH4+ or NO3-, in wet deposition dominated areas, such as hilltops and wind exposed woodland edges.

The Effects of Growth Hormone Treatment on Health-Related Quality of Life in Children

BACKGROUND/AIMS

The effects of growth hormone deficiency (GHD) on linear growth in children are well documented, but there is less convincing evidence regarding the impact on health-related quality of life (QOL). We examined QOL in children aged 8-16 years with acquired GHD following treatment for malignancy (AGHD) or idiopathic GHD (IGHD) on commencing growth hormone treatment (GHT) over 6 months. We adopted a longitudinal design involving consecutive patients and their families attending clinic over an 18-month period. Mothers and children were invited to complete questionnaires before GHT (T1) and 6 months later (T2).

METHODS

Mothers of 22 children (AGHD n = 14; IGHD n = 8) completed standardized measures of child QOL and behaviour. Children completed parallel measures of QOL, short-term memory tasks and fitness either in clinic or at the family home.

RESULTS

For children with AGHD, QOL was significantly below population norms at T1 and improved over time. For children diagnosed with IGHD, QOL at T1 was below, but comparable with population norms. QOL improved over time, though not significantly.

CONCLUSION

GHT is potentially valuable for improving QOL in children, especially in cases of AGHD. We conclude that benefits of GHT for QOL need to be evaluated independent of different diagnostic groups.

The contribution of a comprehensive stroke unit to the outcome of Chinese stroke patients

INTRODUCTION

There are significant differences in stroke patterns and risk factors for cerebrovascular disease between Chinese subjects and Caucasians. The outcome of stroke unit care in a Chinese population has not been described in the medical literature. The present study aims to evaluate the outcome of stroke unit care in Chinese subjects.

METHODS

By prospective comparative research, Chinese patients treated in the stroke unit were group-matched with those treated in the general medical ward by age, gender, premorbid functional status (by the Barthel Index), National Institute of Health Stroke Scale score, and stroke types. From April 2001 to April 2002, a total of 188 patients in the stroke unit group and 177 patients in the general ward group were recruited in the study. The main outcome measures included mortality at 28 and 120 days, and the length of inpatient stay.

RESULTS

Stroke unit care significantly reduced mortality of patients with acute stroke after 28 and 120 days. After 28 days, mortality was 3.3 percent and 17.2 percent for the stroke unit group and general ward group, respectively (p-value is equal to or less than 0.01); whereas after 120 days, mortality was 5.0 percent and 24.7 percent for the stroke unit group and general ward group, respectively (p-value is equal to or less than 0.001). The stroke unit care was demonstrated, by logistic regression analysis, to have contributed to the reduction of mortality at 120 days (p-value is 0.014). At 28 days, there was only a trend for stroke unit care to contribute to the reduction of mortality by logistic regression analysis (p-value is 0.067). By Kaplan-Meier survival curves (log rank statistic is 10.46, p-value is 0.001) and a Cox regression (hazard ratio 0.253, 95 percent confidence interval 0.085 to 0.754, p-value is 0.014), the stroke unit care was further found to reduce mortality significantly. The mean length of inpatient stay of the stroke unit group was 37.1 days, while that of the general medical ward group was 69.3 days (p-value is equal to or less than 0.001).

CONCLUSION

Chinese subjects receiving comprehensive stroke unit care are associated with less mortality and shorter length of hospital stay than those having conventional care in general medical wards.

International Programme for Resource Use in Critical Care (IPOC)--a methodology and initial results of cost and provision in four European countries

BACKGROUND

A standardized top-down costing method is not currently available internationally. An internally validated method developed in the UK was modified for use in critical care in different countries. Costs could then be compared using the World Health Organization's Purchasing Power Parities (WHO PPPs).

METHODS

This was an observational, retrospective, cross-sectional, multicentre study set in four European countries: France, UK, Germany and Hungary. A total of 329 adult intensive care units (ICUs) participated in the study.

RESULTS

The costs are reported in international dollars ($) derived from the WHO PPP programme. The results show significant differences in resource use and costs of ICUs over the four countries. On the basis of the sum of the means for the major components, the average cost per patient day in UK hospitals was $1512, in French hospitals $934, in German hospitals $726 and in Hungarian hospitals $280.

CONCLUSIONS

The reasons for such differences are poorly understood but warrant further investigation. This information will allow us to better adjust our measures of international ICU costs.

Prospective noise induced changes to hearing among construction industry apprentices

AIMS

To characterise the development of noise induced damage to hearing.

METHODS

Hearing and noise exposure were prospectively monitored among a cohort of newly enrolled construction industry apprentices and a comparison group of graduate students, using standard pure tone audiometry and distortion product otoacoustic emissions (DPOAEs). A total of 328 subjects (632 ears) were monitored annually an average of 3.4 times. In parallel to these measures, noise exposure and hearing protection device (HPD) use were extensively monitored during construction work tasks. Recreational/non-occupational exposures also were queried and monitored in subgroups of subjects. Trade specific mean exposure L(eq) levels, with and without accounting for the variable use of hearing protection in each trade, were calculated and used to group subjects by trade specific exposure level. Mixed effects models were used to estimate the change in hearing outcomes over time for each exposure group.

RESULTS

Small but significant exposure related changes in DPOAEs over time were observed, especially at 4 kHz with stimulus levels (L1) between 50 and 75 dB, with less clear but similar patterns observed at 3 kHz. After controlling for covariates, the high exposure group had annual changes in 4 kHz emissions of about 0.5 dB per year. Pure tone audiometric thresholds displayed only slight trends towards increased threshold levels with increasing exposure groups. Some unexpected results were observed, including an apparent increase in DPOAEs among controls over time, and improvement in behavioural thresholds among controls at 6 kHz only.

CONCLUSIONS

Results indicate that construction apprentices in their first three years of work, with average noise exposures under 90 dBA, have measurable losses of hearing function. Despite numerous challenges in using DPOAEs for hearing surveillance in an industrial setting, they appear somewhat more sensitive to these early changes than is evident with standard pure tone audiometry.

Predictors of hearing threshold levels and distortion product otoacoustic emissions among noise exposed young adults

AIM

To examine the relations between noise exposure and other risk factors with hearing function as measured by audiometric thresholds and distortion product otoacoustic emissions.

METHODS

A total of 456 subjects were studied (393 apprentices in construction trades and 63 graduate students). Hearing and peripheral auditory function were quantified using standard, automated threshold audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAEs). The analysis addressed relations of noise exposure history and other risk factors with hearing threshold levels (HTLs) and DPOAEs at the baseline test for the cohort.

RESULTS

The cohort had a mean age of 27 (7) years. The construction apprentices reported more noise exposure than students in both their occupational and non-occupational exposure histories. A strong effect of age and years of work in construction was observed at 4, 6, and 8 kHz for both HTLs and DPOAEs. Each year of construction work reported prior to baseline was associated with a 0.7 dB increase in HTL or 0.2 dB decrease DPOAE amplitude. Overall, there was a very similar pattern of effects between the HTLs and DPOAEs.

CONCLUSIONS

This analysis shows a relatively good correspondence between the associations of noise exposures and other risk factors with DPOAEs and the associations observed with pure-tone audiometric thresholds in a young adult working population. The results provide further evidence that DPOAEs can be used to assess damage to hearing from a variety of exposures including noise. Clarifying advantages of DPOAEs or HTLs in terms of sensitivity to early manifestations of noise insults, or their utility in predicting future loss in hearing will require longitudinal follow up.

The cost of a hospital ward in Europe: is there a methodology available to accurately measure the costs?

Costing health care services has become a major requirement due to an increase in demand for health care and technological advances. Several studies have been published describing the computation of the costs of hospital wards. The objective of this article is to examine the methodologies utilised to try to describe the basic components of a standardised method, which could be applied throughout Europe. Cost measurement however is a complex matter and a lack of clarity exists in the terminology and the cost concepts utilised. The methods discussed in this review make it evident that there is a lack of standardized methodologies for the determination of accurate costs of hospital wards. A standardized costing methodology would facilitate comparisons, encourage economic evaluation within the ward and hence assist in the decision-making process with regard to the efficient allocation of resources.

Accuracy of task recall for epidemiological exposure assessment to construction noise

AIMS

To validate the accuracy of construction worker recall of task and environment based information; and to evaluate the effect of task recall on estimates of noise exposure.

METHODS

A cohort of 25 construction workers recorded tasks daily and had dosimetry measurements weekly for six weeks. Worker recall of tasks reported on the daily activity cards was validated with research observations and compared directly to task recall at a six month interview.

RESULTS

The mean L(EQ) noise exposure level (dBA) from dosimeter measurements was 89.9 (n = 61) and 83.3 (n = 47) for carpenters and electricians, respectively. The percentage time at tasks reported during the interview was compared to that calculated from daily activity cards; only 2/22 tasks were different at the nominal 5% significance level. The accuracy, based on bias and precision, of percentage time reported for tasks from the interview was 53-100% (median 91%). For carpenters, the difference in noise estimates derived from activity cards (mean 91.9 dBA) was not different from those derived from the questionnaire (mean 91.7 dBA). This trend held for electricians as well. For all subjects, noise estimates derived from the activity card and the questionnaire were strongly correlated with dosimetry measurements. The average difference between the noise estimate derived from the questionnaire and dosimetry measurements was 2.0 dBA, and was independent of the actual exposure level.

CONCLUSIONS

Six months after tasks were performed, construction workers were able to accurately recall the percentage time they spent at various tasks. Estimates of noise exposure based on long term recall (questionnaire) were no different from estimates derived from daily activity cards and were strongly correlated with dosimetry measurements, overestimating the level on average by 2.0 dBA.

Exposure to ambient fine particulate matter and primary cardiac arrest among persons with and without clinically recognized heart disease

The authors studied the association between incidence of primary cardiac arrest and daily measures of fine particulate matter (</=2.5 micro m) using a case-crossover study of 1,206 Washington State out-of-hospital cardiac arrests (1985-1994) among persons with (n = 774) and without (n = 432) clinically recognized heart disease. The authors compared particulate matter levels on the day of the cardiac event and the 2 days preceding the event with levels from matched reference days. The estimated relative risk for a 13.8- micro g/m(3) increase in fine particulate matter (nephelometry: 0.54 x 10(-1) km(-1 )bsp) on the day prior to cardiac arrest was 0.94 (95% confidence interval: 0.88, 1.02). Pollutant levels measured on the same day as the event and on the 2 days preceding the event demonstrated similar results. No increased risk was found among all cases with preexisting cardiac disease (odds ratio = 0.97, 95% confidence interval: 0.89, 1.07); however, an unexpected association appeared between current smokers with preexisting heart disease and increased particulate matter levels 2 days prior to the event (odds ratio = 1.29, 95% confidence interval: 1.06, 1.55). This association was not present in the 0- or 1-day lag analyses or in persons with other diseases. There was no consistent association between increased levels of fine particulate matter and risk of primary cardiac arrest.

Work practices of rural and remote physiotherapists

Physiotherapists in rural and remote areas face challenges in their service delivery. The challenge is to provide accessible and comprehensive services to rural and remote Australians. Research was undertaken regarding the work practices of physiotherapists and the availability of other health professionals in rural and remote South Australia and Northern Territory. Rural and remote area physiotherapists in this study are likely to be sole practitioners with a generalist practice. The high number who have practising rights at public hospitals gives rise to service delivery with a wide range of clients and reduced opportunity for specialisation. In addition, the demand for physiotherapists to be multiskilled is increased with the lower number of resident medical specialists and allied health professionals in rural areas. Greater access to other professionals for rural and remote Australians may come from the development of resource networks supported by regional organisation of resources and infrastructure.

Correcting for the effects of location and atmospheric conditions on air pollution exposures in a case-crossover study

A limitation of most air pollution health effects studies is that they rely on monitoring data averaged over one or more ambient monitors to represent daily air pollution exposures for individuals. Such data analyses therefore implicitly require the assumption of a homogeneous spatial distribution for particulate matter (PM). This assumption may be suspected in the Pacific Northwest because of its hilly topography and local variations in wood burning. To examine the bias from substituting regional PM (i.e., the average of three ambient monitor measurements) for individual PM exposure, we conducted an exposure substudy to identify the influence of location factors, specifically urban versus suburban classification and topographic features ("upstream" versus "downstream"), on local ambient measurements. Using nephelometer measurements collected over 1 year in four locations, we developed regression models to predict local PM as a function of regional PM, atmospheric stagnation, temperature, and location. We found a significant interaction between atmospheric stagnation and topography, with the most upstream site having reduced PM levels on high stagnation days after controlling for regional PM. We also found a significant interaction with temperature at one downstream site thought to be heavily exposed to wood smoke in the winter. These results are consistent with the physics of surface radiation inversions. The interactions reordered the index versus referent exposures in a case-crossover analysis of out-of-hospital primary cardiac arrest for subjects living in specific locations, but did not meaningfully change the associations with PM from the analysis using regional PM as the exposure. The lack of change in these results may be due to limitations in the data used to correct the exposure estimates or to the absence of a PM effect among persons without prior heart disease who experienced a primary cardiac arrest.

Referent selection in case-crossover analyses of acute health effects of air pollution

The case-crossover design was proposed for the study of a transient effect of an intermittent exposure on the subsequent occurrence of a rare acute-onset disease. This design can be an alternative to Poisson time series regression for studying the health effects of fine particulate matter air pollution. Characteristics of time-series of particulate matter, including long-term time trends, seasonal trends, and short-term autocorrelations, require that referent selection in the case-crossover design be considered carefully and adapted to minimize bias. We performed simulations to evaluate the bias associated with various referent selection strategies for a proposed case-crossover study of associations between particulate matter and primary cardiac arrest. Some a priori reasonable strategies were associated with a relative bias as large as 10%, but for most strategies the relative bias was less than 2% with confidence interval coverage within 1% of the nominal level. We show that referent selection for case-crossover designs raises the same issues as selection of smoothing method for time series analyses. In addition, conditional logistic regression analysis is not strictly valid for some case-crossover designs, introducing further bias.

A case-crossover analysis of particulate matter air pollution and out-of-hospital primary cardiac arrest

Numerous epidemiologic studies have reported increases in the daily incidence of cardiovascular mortality and morbidity associated with increases in daily levels of particulate matter air pollution. We studied the association between the incidence of primary cardiac arrest and two daily measures of particulate matter using a case-crossover study of 362 cases of out-of-hospital cardiac arrest. All cases were attended by paramedics and had no history of clinically recognized heart disease or life-threatening comorbidities. We compared particulate matter levels at index times with particulate matter levels from referent days matched on day of week within strata defined by month and year. The estimated relative risk at a lag of 1 day for an interquartile range (IQR) change in nephelometry (0.51 x 10(-1) km(-1)) was 0.893 (95% CI = 0.779-1.024). The estimated relative risk at a lag of 1 day for an IQR change in PM10 (19.3 microg m(-3)) was 0.868 (95% CI = 0.744-1.012). Other lag periods gave similar results. We did not find evidence of confounding by carbon monoxide or sulfur dioxide. Analysis of effect modification by individual-level variables did not reveal any susceptible subgroups. These findings do no support an association between particulate matter and increased risk of primary cardiac arrest among persons without clinically recognized heart disease. The null results of this study may result from several factors, including the highly selected nature of this case series and the relatively low particulate matter levels in the Seattle metropolitan area.

Effects of ambient air pollution on symptoms of asthma in Seattle-area children enrolled in the CAMP study

We observed a panel of 133 children (5-13 years of age) with asthma residing in the greater Seattle, Washington, area for an average of 58 days (range 28-112 days) during screening for enrollment in the Childhood Asthma Management Program (CAMP) study. Daily self-reports of asthma symptoms were obtained from study diaries and compared with ambient air pollution levels in marginal repeated measures logistic regression models. We defined days with asthma symptoms as any day a child reported at least one mild asthma episode. All analyses were controlled for subject-specific variables [age, race, sex, baseline height, and FEV(1) PC(20) concentration (methacholine provocative concentration required to produce a 20% decrease in forced expiratory volume in 1 sec)] and potential time-dependent confounders (day of week, season, and temperature). Because of variable observation periods for participants, we estimated both between- and within-subject air pollutant effects. Our primary interest was in the within-subject effects: the effect of air pollutant excursions from typical levels in each child's observation period on the odds of asthma symptoms. In single-pollutant models, the population average estimates indicated a 30% [95% confidence interval (CI), 11-52%] increase for a 1-ppm increment in carbon monoxide lagged 1 day, an 18% (95% CI, 5-33%) increase for a 10-microg/m(3) increment in same-day particulate matter < 1.0 microm (PM(1.0)), and an 11% (95% CI, 3-20%) increase for a 10-microg/m(3) increment in particulate matter < 10 microm (PM(10)) lagged 1 day. Conditional on the previous day's asthma symptoms, we estimated 25% (95% CI, 10-42%), 14% (95% CI, 4-26%), and 10% (95% CI, 3-16%) increases in the odds of asthma symptoms associated with increases in CO, PM(1.0), and PM(10), respectively. We did not find any association between sulfur dioxide (SO(2)) and the odds of asthma symptoms. In multipollutant models, the separate pollutant effects were smaller. The overall effect of an increase in both CO and PM(1. 0) was a 31% (95% CI, 11-55%) increase in the odds of symptoms of asthma. We conclude that there is an association between change in short-term air pollution levels, as indexed by PM and CO, and the occurrence of asthma symptoms among children in Seattle. Although PM effects on asthma have been found in other studies, it is likely that CO is a marker for vehicle exhaust and other combustion by-products that aggravate asthma.

A case-crossover analysis of fine particulate matter air pollution and out-of-hospital sudden cardiac arrest

Numerous recent epidemiologic studies report increases in the daily incidence of cardiovascular disease mortality and morbidity related to increases in daily levels of fine particulate matter (PM)* air pollution. This study sought to evaluate the possible association between the occurrence of out-of-hospital sudden cardiac arrest (SCA) and daily PM levels in the Seattle metropolitan area. The underlying hypothesis was that PM exposure may act as a cardiovascular trigger for SCA. A case-crossover study was conducted among 362 SCA cases identified by paramedics from October 1988 through June 1994. Cases were King County WA residents who were married, aged 25 to 74 years at the time of their SCA, with no prior history of clinically recognized heart disease or other life-threatening comorbid conditions. Daily averages of regional PM monitoring data for nephelometry measures of PM (reported in units of bsp, referred to as coefficient of light scattering) and PM10 (particulate matter 10 microm or smaller in aerodynamic diameter) from three monitoring sites were used as indicators of exposure. In the case-crossover analysis, PM levels during index times of cases within the five days preceding an SCA were compared with PM levels at referent days, defined as the same days of the week during the month of SCA occurrence. Lag periods for index days of 0 to 5 days were investigated. The estimated relative risk (RR) at a lag of 1 day for an interquartile range (IQR) change in nephelometry (0.51 bsp) was 0.893 (95% confidence interval [CI] 0.779-1.024). Varying the lag period had only minimal change on the observed association. The estimated relative risk at a lag of 1 day for an IQR change of PM10 (19.3 microg/m3) was 0.868 (95% CI 0.744-1.012). There was no evidence of confounding by ambient daily exposures to carbon monoxide or sulfur dioxide. Analysis of effect modification by individual-level variables, including age, cigarette smoke exposure, physical activity, and other risk or protective factors for cardiovascular disease did not reveal any susceptible subgroups. The null results of this study may be due to several factors; these include: the highly selected nature of this SCA case series; the fact that cases were free of prior clinically recognized heart disease or major life-threatening comorbidity; and the possibility that PM exposures at the relatively low levels seen in the Seattle metropolitan area do not trigger cardiovascular toxic mechanisms that culminate in SCA.

People with dementia use schemata to support episodic memory

This paper describes two experiments which examine whether people with dementia use schemata, established knowledge stores associated with specific scenarios, to aid episodic memory. On all tests of memory, volunteers with dementia remembered less than their age-matched controls. There was evidence for an age-related decline in cognitive resources available for effortful memorizing. For people with dementia, errors of commission in free recall, false recognition scores and reconstruction data were consistent with the use of schema to guide retrieval of items from memory. We conclude that retrieval support improves memory performance for both the healthy and dementing elderly. More importantly, pre-established schemata remain intact well into the course of dementia and can support recall of newly acquired episodic information.

Molecular breeding of viruses

Genetic recombination is a major force driving the evolution of many viruses. Recombination between two copackaged retroviral genomes may occur at rates as high as 40% per replication cycle. This enables genetic information to be shuffled rapidly, leading to recombinants with new patterns of mutations and phenotypes. The in vitro process of DNA shuffling (molecular breeding) mimics this mechanism on a vastly parallel and accelerated scale. Multiple homologous parental sequences are recombined in parallel, leading to a diverse library of complex recombinants from which desired improvements can be selected. Different proteins and enzymes have been improved using DNA shuffling. We report here the first application of molecular breeding to viruses. A single round of shuffling envelope sequences from six murine leukaemia viruses (MLV) followed by selection yielded a chimaeric clone with a completely new tropism for Chinese Hamster Ovary (CHOK1) cells. The composition and properties of the selected clone indicated that this particular permutation of parental sequences cannot be readily attained by natural retroviral recombination. This example demonstrates that molecular breeding can enhance the inherently high evolutionary potential of retroviruses to obtain desired phenotypes. It can be an effective tool, when information is limited, to optimize viruses for gene therapy and vaccine applications when multiple complex functions must be simultaneously balanced.

Asthma aggravation, combustion, and stagnant air

BACKGROUND

The relationship between current concentrations of ambient air pollution and adverse health effects is controversial. We report a meteorological index of air stagnation that is associated with daily visits to the emergency department for asthma in two urban areas.

METHODS

Data on daily values of a stagnation persistence index and visits to the emergency department for asthma were collected for approximately two years in Spokane, Washington, USA and for 15 months in Seattle, Washington, USA. The stagnation persistence index represents the number of hours during the 24 hour day when surface wind speeds are less than the annual hourly median value, an index readily available for most urban areas. Associations between the daily stagnation persistence index and daily emergency department visits for asthma were tested using a generalised additive Poisson regression model. A factor analysis of particulate matter (PM(2.5)) composition was performed to identify the pollutants associated with increased asthma visits.

RESULTS

The relative rate of the association between a visit to the emergency department for asthma and the stagnation persistence index was 1. 12 (95% CI 1.05 to 1.19) in Spokane and 1.21 (95% CI 1.09 to 1.35) in Seattle for an increase of 11 and 10 hours, respectively, of low wind speed in a given day. The stagnation persistence index was only correlated with one set of factor loadings; that cluster included the stagnation persistence index, carbon monoxide, and organic/elemental carbon.

CONCLUSION

Increased air stagnation was shown to be a surrogate for accumulation of the products of incomplete combustion, including carbon monoxide and fine particulate levels of organic and elemental carbon, and was more strongly associated with asthma aggravation than any one of the measured pollutants.

Reproductive and offspring developmental effects following maternal inhalation exposure to methanol in nonhuman primates

INTRODUCTION

In an effort to improve air quality and decrease dependence on petroleum, the federal government, industry, and other groups have encouraged development of alternative fuels such as methanol to substitute for gasoline or diesel fuel. Methanol is also a candidate to provide the hydrogen for fuel cells, which are being developed for a variety of power sources (including motor vehicle engines). Before people are exposed to increased concentrations of methanol, the potential health effects of such exposures require study. Methanol, a simple alcohol containing one carbon atom, occurs naturally in plants and animals and participates in human metabolism. People regularly consume low doses of methanol in fruits, vegetables, and fermented beverages as well as soft drinks and foods sweetened with aspartame (which breaks down to methanol in the gastrointestinal tract). Despite its ubiquitous presence, methanol can be highly toxic if sufficient quantities are consumed. Ingestion of methanol (usually in the form of wood alcohol or tainted alcoholic beverages) can result in metabolic acidosis, blindness, and even death. Although the body has the capacity to metabolize the low doses of methanol to which people are regularly exposed, it cannot handle high doses because too much methanol overwhelms the body's ability to remove a toxic metabolite (formate). When formate accumulates, methanol poisoning occurs. One factor that regulates the rate at which formate is removed is the liver level of a derivative of the vitamin folic acid. People who are deficient in folic acid (including 15% to 30% of pregnant women) may be particularly susceptible to the toxic effects of methanol. If methanol were to be widely adopted as a fuel, environmental exposures would increase through ingestion of contaminated drinking water, inhalation of vapors from evaporative and other emissions, and dermal contact. Current concentrations of methanol in ambient air are very low, 1 to 30 parts per billion (ppb). If all motor vehicles in the United States were converted to 100% methanol fuel, methanol levels in ambient air are estimated to increase approximately 1,000-fold (to 1 to 10 ppm in cities) and in a worst-case situation could occasionally reach concentrations as high as 200 ppm in enclosed spaces (HEI 1987). Inhaling these concentrations of methanol for short periods of time is not predicted to affect formate production and thus should not present a health risk. However, little is known about the consequences of long-term inhalation of methanol vapors, especially in susceptible populations of pregnant women and developing fetuses. HEI, therefore, developed a research program to address this information gap.

APPROACH

Dr. Thomas Burbacher and colleagues of the University of Washington studied the effects of long-term exposure to methanol vapors on metabolism and reproduction in adult female monkeys (Macaca fascicularis) and developmental effects in their offspring, who were exposed prenatally to methanol. The investigators exposed adult female monkeys (11 to 12 animals/group) to one of four concentrations of methanol vapors (0, 200, 600, and 1,800 ppm) for 2.5 hours a day, seven days a week during the following periods: (1) before breeding, (2) during breeding, and (3) during pregnancy. They collected blood from the adults at regular intervals to monitor methanol levels (which served as a marker of internal dose) and formate concentrations. They also conducted pharmacokinetic studies to determine whether methanol disposition (which includes absorption, distribution, metabolism, and excretion) was altered as a result of repeated methanol exposures and to assess pregnancy-related changes. Because high doses of methanol damage the central nervous system, the infants (8 to 9 animals/group) were examined at regular intervals during the first nine months of life to assess their growth and neurobehavioral development.

RESULTS

Exposure to methanol vapors did n

Variability in annual Mini-Mental State Examination score in patients with probable Alzheimer disease: a clinical perspective of data from the Consortium to Establish a Registry for Alzheimer's Disease

OBJECTIVE

To determine the variability in annual Mini-Mental State Examination scores of patients with Alzheimer disease enrolled in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD).

PATIENTS

A total of 372 patients with probable Alzheimer disease with 1 or more years of follow-up.

SETTING

Twenty-one CERAD clinical sites throughout the United States.

RESULTS

An average annual decline of 3.4 points in CERAD patients returning for longitudinal reassessments was close to the SD of the measurement error of 2.8 points for the Mini-Mental State Examination. There was wide variability in individual rates of decline. Even with 4 years of follow-up, 15.8% of the patients had no clinically meaningful decline in Mini-Mental State Examination score (defined as a change in initial score >3, ie, 1 SD of measurement error). Validity of measurements of the rate of change in Mini-Mental State Examination scores improved with longer observation intervals and was reliable for most patients when observations were separated by 3 or more years.

CONCLUSIONS

Although the Mini-Mental State Examination is a useful screening instrument to assess level of cognitive function, it has limited value in measuring the progression of Alzheimer disease in individual patients for periods less than 3 years because of a large measurement error and substantial variation in change in annual score.

An association between fine particles and asthma emergency department visits for children in Seattle

Asthma is the most common chronic illness of childhood and its prevalence is increasing, causing much concern for identification of risk factors such as air pollution. We previously conducted a study showing a relationship between asthma visits in all persons < 65 years of age to emergency departments (EDs) and air pollution in Seattle, Washington. In that study the most frequent zip codes of the visits were in the inner city. The Seattle-King County Department of Public Health (Seattle, WA) subsequently published a report which showed that the hospitalization rate for children in the inner city was over 600/100,000, whereas it was < 100/100,000 for children living in the suburbs. Therefore, we conducted the present study to evaluate whether asthma visits to hospital emergency departments in the inner city of Seattle were associated with outdoor air pollution levels. ED visits to six hospitals for asthma and daily air pollution data were obtained for 15 months during 1995 and 1996. The association between air pollution and childhood ED visits for asthma from the inner city area with high asthma hospitalization rates were compared with those from lower hospital utilization areas. Daily ED counts were regressed against fine particulate matter (PM), carbon monoxide (CO), sulfur dioxide, and nitrogen dioxide using a semiparametric Poisson regression model. Significant associations were found between ED visits for asthma in children and fine PM and CO. A change of 11 microg/m3 in fine PM was associated with a relative rate of 1.15 [95% confidence interval (CI), 1.08-1.23]. There was no stronger association between ED visits for asthma and air pollution in the higher hospital utilization area than in the lower utilization area. These findings were seen when estimated PM2.5 concentrations were below the newly adopted annual National Ambient Air Quality Standard of 15 microg/m3.

An association between fine particles and asthma emergency department visits for children in Seattle

Asthma is the most common chronic illness of childhood and its prevalence is increasing, causing much concern for identification of risk factors such as air pollution. We previously conducted a study showing a relationship between asthma visits in all persons < 65 years of age to emergency departments (EDs) and air pollution in Seattle, Washington. In that study the most frequent zip codes of the visits were in the inner city. The Seattle-King County Department of Public Health (Seattle, WA) subsequently published a report which showed that the hospitalization rate for children in the inner city was over 600/100,000, whereas it was < 100/100,000 for children living in the suburbs. Therefore, we conducted the present study to evaluate whether asthma visits to hospital emergency departments in the inner city of Seattle were associated with outdoor air pollution levels. ED visits to six hospitals for asthma and daily air pollution data were obtained for 15 months during 1995 and 1996. The association between air pollution and childhood ED visits for asthma from the inner city area with high asthma hospitalization rates were compared with those from lower hospital utilization areas. Daily ED counts were regressed against fine particulate matter (PM), carbon monoxide (CO), sulfur dioxide, and nitrogen dioxide using a semiparametric Poisson regression model. Significant associations were found between ED visits for asthma in children and fine PM and CO. A change of 11 microg/m3 in fine PM was associated with a relative rate of 1.15 [95% confidence interval (CI), 1.08-1.23]. There was no stronger association between ED visits for asthma and air pollution in the higher hospital utilization area than in the lower utilization area. These findings were seen when estimated PM2.5 concentrations were below the newly adopted annual National Ambient Air Quality Standard of 15 microg/m3.

Episodes of high coarse particle concentrations are not associated with increased mortality

Fine particle concentration (i.e., particles <2.5 microm in aerodynamic diameter; PM2.5), but not coarse particle concentration, was associated with increased mortality in six U.S. cities. Others criticized this result, arguing that it could result from differences in measurement error between the two size ranges. Fine particles are primarily from combustion of fossil fuel, whereras coarse particles (i.e., particles between 2.5 and 10 microm in aerodynamic diameter) are all crustal material, i.e., dust. One way to determine if coarse particles are a risk for mortality is to identify episodes of high concentrations of coarse, but not fine, particles. Spokane, Washington, is located in an arid area and is subject to occasional dust storms after crops have been harvested. Between 1989 and 1995, we identified 17 dust storms in Spokane. The 24-hr mean PM10 concentration during those storms was 263 microg/m3. Using control dates that were the same day of the year in other years (but with no dust storm on that day) and that had a mean PM10 concentration of 42 microg/m3, we compared the rate of nonaccidental deaths on the episode versus nonepisode days. There was little evidence of any risk [relative risk (RR) = 1.00; 95% confidence interval (CI), 0.81-1.22] on the episode days. Defining episode deaths as those occurring on the same or following day as the dust storm produced similar results (RR = 1.01; CI, 0.87-1.17). Sensitivity analyses, which tested more extensive seasonal control, produced smaller estimates. We conclude that coarse particles from windblown dust are not associated with mortality risk.

Differences in stakeholder expectations in the outcome of physiotherapy management of acute low back pain

OBJECTIVE

To compare stakeholder expectations of outcome of physiotherapy management of acute low back pain.

DESIGN

Observational design using interviews and questionnaires.

SETTING

Practice/workplace.

STUDY PARTICIPANTS

The study sample was from South Australia. It comprised 74 physiotherapists randomly selected from professional association listings (49.3% response rate), 121 physiotherapy patients (recruited by participating physiotherapists when attending their first physiotherapy treatment for acute low back pain), 21 general practitioners randomly selected from medical practitioner listings in the metropolitan telephone book (36.2% response rate) and 13 third party payers of a total of 16 available insurers in the metropolitan area (82% response rate).

MAIN OUTCOME MEASUREMENTS

Stakeholders reported expectations of outcome at the end of the first treatment session and at the completion of the episode of care.

RESULTS

There were differences in expectations between stakeholders, as well as between naive and experienced patients. Overall, patients expected symptom relief at the end of the first treatment. Naive patients decided to return for further treatment based on the relationship established with the therapist, whereas experienced patients also expected some advice on their condition during the first contact. Physiotherapists and referrers expected symptom relief and then long-term management strategies to be provided, and third party payers expected cost-efficient management of the condition and patient satisfaction.

CONCLUSION

Physiotherapists need to address potential imbalance of consumer knowledge and foster a quality partnership with their patients on the first visit to physiotherapy. Patients who are in pain may not derive full value from information provided in an untimely manner.

Effects of ambient air pollution on nonelderly asthma hospital admissions in Seattle, Washington, 1987-1994

As part of the Clean Air Act, Congress has directed EPA to set air quality standards to protect sensitive population groups from air pollutants in the ambient environment. People with asthma represent one such group. We undertook a study of the relation between measured ambient air pollutants in Seattle and nonelderly hospital admissions with a principal diagnosis of asthma. We regressed daily hospital admissions to local hospitals for area residents from 1987 through 1994 on particulate matter less than 10 and 2.5 microm in aerodynamic diameter (PM10 and PM2.5, respectively); coarse particulate mass; sulfur dioxide (SO2); ozone (O3); and carbon monoxide (CO) in a Poisson regression model with control for time trends, seasonal variations, and temperature-related weather effects. With the exception of seasonally monitored O3, we supplemented incomplete pollutant measures in a multiple imputation model to create a complete time series of exposure measures. We found an estimated 4-5% increase in the rate of asthma hospital admissions associated with an interquartile range change in PM (19 microg/m3 PM(10),11.8 microg/m3 PM2.5, and 9.3 microg/m3 coarse particulate mass) lagged 1 day; relative rates were as follows: for PM10, 1.05 [95% confidence interval (CI) = 1.02-1.08]; for PM2.5, 1.04 (95% CI = 1.02-1.07); and for coarse particulate mass, 1.04 (95% CI = 1.01-1.07). In single-pollutant models we also found that a 6% increase in the rate of admission was associated with an interquartile range change in CO (interquartile range, 924 parts per billion; 95% CI = 1.03-1.09) at a lag of 3 days and an interquartile range change in O3 (interquartile range, 20 parts per billion; 95% CI = 1.02-1.11) at a lag of 2 days. We did not observe an association for SO2. We found PM and CO to be jointly associated with asthma admissions. We estimated the highest increase in risk in the spring and fall seasons.

Technology in education: what is appropriate for rural and remote allied health professionals?

Recent technological advances provide exciting opportunities for the delivery of education to rural and remote allied health professionals. Distance education modes can overcome barriers of distance and cost. However, the use of technologies may allow distance education to be more interactive for rural and remote professionals. Technologies that can be used are audioconferencing, videoconferencing, electronic mail (email), CD-ROM and the Internet. Combinations of any of these technologies and traditional forms of educational delivery are possible. The important objective is to create a learning environment that maximises interactivity and develops information literacy.

The validity of radiographic estimation of total lung capacity in patients with respiratory disease

STUDY OBJECTIVE

To evaluate the validity of a state-of-the-art computerized planimetry technique for estimation of total lung capacity (TLC) from chest radiographs, when applied to patients with clinical lung disease receiving routine chest radiographs.

DESIGN

Retrospective clinical survey.

SETTING

An occupational medicine diagnostic clinic.

PATIENTS

A convenience sample of 40 subjects with asbestos-related lung disease, 5 patients with nonasbestos-related restrictive defects, 15 subjects with occupational asthma, and 10 subjects with irritant tracheobronchitis.

RESULTS

Estimation of TLC using state-of-the-art computerized algorithms demonstrated limited agreement with conventional measures of TLC when applied to patients with occupational lung disease receiving routine chest radiographs. The most pronounced differences occurred in patients with asbestos-related lung disease and restrictive defects, where the radiographic method of measurement significantly overestimated helium dilution TLC by 986 mL (r=0.73, p<0.001) and 1,135 mL (r=0.82, p<0.05), respectively. Good inspiratory effort was associated with significantly increased radiographic TLC relative to helium dilution TLC; however, radiographic features did not fully account for the observed differences between radiographic and helium dilution techniques.

CONCLUSIONS

Our findings suggest that this planimetric technique should not be used as a substitute for conventional measures of TLC in clinic populations receiving routine radiographs. The large diagnostic group specific mean differences observed between radiographic and conventional measures of TLC also suggest that this method is of limited utility in clinical evaluation of occupational lung disease.

Head injury and risk of Alzheimer's disease by apolipoprotein E genotype

Head injury and apolipoprotein E (APOE)-epsilon 4 (e4) genotype have each been associated with increased risk of Alzheimer's disease. If APOE-e4 affects neuronal viability and branching, and if response to head injury differs in e4 patients, then the association between head injury and Alzheimer's disease may vary with the presence of the e4 allele. The authors examined this association in a case-control study conducted between 1987 and 1995 among enrollees of the Group Health Cooperative of Puget Sound, a health maintenance organization in Seattle, Washington. Proxy informants reported prior head injury with loss of consciousness for 32 of 349 patients with probable Alzheimer's disease and for 16 of 342 control subjects of similar age and sex who had been randomly selected from the same population (odds ratio (OR) = 2.1, 95% confidence interval (CI) 1.1-3.8). Elevated risk was observed among men (OR = 4.2, 95% CI 1.5-11.5) but not among women (OR = 1.1, 95% CI 0.5-2.6). No significant variation in the head injury-Alzheimer's disease risk relation by APOE-e4 genotype was found among 230 cases and 309 controls (OR = 3.1 (95% CI 0.7-14.6) for persons with at least one e4 allele and OR = 2.0 (95% CI 0.8-5.2) for those without e4). Neither age, education, race, type of proxy informant, nor duration of relationship with the proxy confounded the association. Head injury with loss of consciousness, although uncommon in this sample, was associated with increased risk of Alzheimer's disease. APOE-e4 was an independent risk factor which neither modified nor confounded the association. Susceptibility to Alzheimer's disease as conferred by APOE-e4 does not appear to increase the risk associated with head injury.

Tuberculosis in health care settings and the estimated benefits of engineering controls and respiratory protection

Intra-institutional spread of tuberculosis (Tb) has re-emerged as a substantial public and occupational health threat. To characterize the person-hours and lifetime risks of Tb-related morbidity and mortality, we performed a risk assessment for health care workers (HCWs) developing Tb-related morbidity and mortality at varying levels of exposure, engineering controls, and respiratory protection. Under average conditions of exposure, one Tb skin-test conversion is estimated to occur for every 2650 person-hours of work by unprotected workers. With higher exposures, a skin-test conversion for an unprotected worker may occur in as few as 3 person-hours. Use of respiratory protection is estimated to reduce risks by the following proportions: surgical mask, 2.4-fold; disposable dust, fume, mist, or disposable high-efficiency particulate air filtering (HEPA) mask, 17.5-fold; elastomeric HEPA cartridge respirator, 45.5-fold; or powered air-purifying respirator (PAPR), 238-fold. Assuming a lifetime exposure of 250 hours, the risk of a skin-test conversion is estimated to be 9%. We conclude that HCWs are at substantial risk for Tb-related morbidity and mortality, and that administrative controls, engineering controls, and respirators offer substantial benefits in risk reduction.

Intracranial aneurysms: detection and characterization with MR angiography with use of an advanced postprocessing technique in a blinded-reader study

PURPOSE

To assess magnetic resonance (MR) angiography for the detection and characterization of angiographically proved intracranial aneurysms by using an advanced method of postprocessing, in a blinded-reader study.

MATERIALS AND METHODS

One hundred fifty-eight vessels were examined with catheter angiography and three-dimensional time-of-flight MR angiography in 44 patients with 63 aneurysms and 15 patients with no aneurysm at catheter angiography. Postprocessing was performed off-line with an advanced multifeature-extraction, ray-tracing algorithm. MR angiograms were interpreted independently by three neuroradiologists blinded to the catheter angiographic results for presence, location, size, and morphology of the aneurysm. Proof of diagnosis was consensus reading of catheter angiograms.

RESULTS

Mean sensitivity for detection of aneurysms was 75% (range, 70%-79%). As a screening tool (ie, detection of at least one aneurysm necessitating catheter angiography), mean sensitivity was 91% for all aneurysms and 95% for aneurysms larger than 3 mm. This method was not adequate for detection of lobulation or size of aneurysm.

CONCLUSION

MR angiography with an advanced method of postprocessing can result in highly sensitive, specific studies for the diagnosis of intracranial aneurysms that are of sufficient size to be considered for surgical treatment, but it is inadequate for characterization of aneurysms.

Design considerations for estimation of exposure effects on disease risk, using aggregate data studies

Previously we proposed an aggregate data study design for estimation of exposure effects from population-based disease rates and covariate data from risk factor surveys in each population group. A basic relative rate model specified for individuals is aggregated to produce a random effects relative rate model for the disease rates. Relative rate parameter estimates from aggregate data studies target the same parameters as individual-level studies but use between-group information in the data. We distinguish aggregate data studies from ecologic studies. Considerations in the design of aggregate studies are motivated by the need to gain clearer understanding of the role of diet in cancer aetiology. Simulation studies show that increasing the number of populations included in an aggregate data study from about 20 to 30-40 gives greater improvement in power than corresponding increases in the size of the survey sample in each population over an initial size of 100 individuals.

Predictors of mortality in patients diagnosed with probable Alzheimer's disease

OBJECTIVE

We sought to identify factors associated with mortality in persons recently diagnosed with probable Alzheimer's disease (AD).

BACKGROUND

Predicting mortality in AD in needed both in patient care and public health planning. Previous studies have identified several factors which contribute to mortality in AD, but few longitudinal studies of population-based cohorts exist.

METHODS

In a longitudinal follow-up study 327 patients with newly diagnosed probable AD (mean Mini-Mental State Examination [MMSE] score of 20) from a large, stable health maintenance organization were identified. Demographic characteristics, dementia severity, and comorbid conditions were identified at enrollment. Patients were followed longitudinally (median 3.3 years, total 898 person-years). Baseline characteristics were used to predict survival in univariate and multivariate models.

RESULTS

Increased mortality was seen in patients with probable AD (9.0 deaths per 100 person-years) compared with the community population adjusted for age and gender (4.3 deaths per 100 person-years). On univariate analysis we found increased age, male gender, impairment on MMSE or Blessed dementia rating scale (DRS), rate of MMSE decline, wandering or agitation, vascular disease, and sensory impairment affecting the ability to read or hear to be moderately associated with decreased survival. After adjusting for age and gender in a multivariate model, Blessed DRS score and sensory impairment affecting the ability to read were independently associated with decreased survival.

CONCLUSIONS

Short-term mortality is increased in patients newly diagnosed with probable AD. Measures of dementia severity, measures of general debility, and vascular disease are associated with increased mortality. Of these, general debility and sensory impairment were more strongly associated with shortened survival.

Impact of sample selection on APOE epsilon 4 allele frequency: a comparison of two Alzheimer's disease samples

OBJECTIVE

In a highly selected sample of unrelated Alzheimer's disease (AD) patients, we found that the APOE epsilon 4 allele frequency was higher than previously reported. Differing selection and ascertainment criteria may lead to these differences. To address this possibility, we compared the epsilon 4 allele frequency in two samples of AD patients selected from the same geographical area.

SETTING AND PARTICIPANTS

Cases (n = 55) and controls (n = 99) from a research clinic-based sample were compared with subjects (n = 537) from a community-based AD patient sample. The samples consisted of unrelated cases who met NINCDS/ADRDA criteria for probable AD.

DESIGN AND MEASUREMENTS

Clinical characteristics and APOE genotype data were obtained from AD cases and controls from both samples.

RESULTS

Frequency of APOE epsilon 4 allele in the research cases compared with the community cases (0.45 vs 0.36) was nearly significant. We compared demographic and clinical characteristics that might account for this difference and found that the research cases were younger, had an earlier age of onset, and had more advanced disease than the community cases. After onset age was controlled, there was no overall difference between epsilon 4 allele frequency of the two samples.

CONCLUSIONS

We found that the epsilon 4 allele frequency tended to be higher in the research AD sample compared the community-based sample. The two samples differed in several demographic and clinical characteristics. We conclude that research-based samples may lead to enrollment of younger patients with more severe disease who have higher APOE epsilon 4 allele load. This potential selection bias must be considered in the interpretation of studies of APOE allele frequency.

Maximizing accuracy and precision using individual and grouped exposure assessments

OBJECTIVES

Random errors in exposure data were explored to determine their effect on exposure-response relationships using individual, grouped, or combined (grouped and individual) exposure assessment methods.

METHODS

Monte Carlo simulations were conducted by generating small "studies" of one hundred subjects divided into four exposure groups. Observed exposure data were generated for each individual using assumed inter- and intraindividual variances and a lognormal distribution. The data were used to calculate the following three estimates of exposure: an individual mean, a group mean, and a hybrid estimate using the James-Stein shrinkage estimator. The exposure estimates were regressed on generated (continuous) "health outcomes," and the regression results were stored and analyzed.

RESULTS

Random errors in exposure data resulted in attenuation of the exposure-response relationship when the individual estimates were used, especially when the within-subject variability was high. The attenuation was substantially controlled by the group mean estimate, however, at a cost of decreased precision. The hybrid estimator simultaneously controlled both bias and imprecision in the observed exposure-response function.

CONCLUSIONS

While estimates of exposure based on individual means may result in attenuation of the exposure-response relationship, grouped estimates may control bias while decreasing precision. Combining individual and group estimates can simultaneously control both types of error. However, further research is required to determine how robust these findings are to different error structures, grouping strategies, exposure-response models, and exposure assessment methods.

Structuring the acquisition and retrieval environment to facilitate learning in individuals with dementia of the Alzheimer type

Three experiments using variations of the Subject Performed Task (SPT) paradigm examined whether structuring the learning and retrieval environment would improve learning in individuals with mild to moderate dementia of the Alzheimer type (DAT). Experiment 1 examined the role of enactment at encoding and retrieval, and found that with appropriate retrieval support DAT volunteers do benefit from enactment at encoding. Experiment 2 showed that recall was further enhanced when the list of SPTs formed a cohesive, goal-directed sequence of actions. In Experiment 3, DAT subjects acquired a more complex action-based sequence and maintained it accurately over a short period of time. It is concluded that the provision of contextual support at encoding and at retrieval can enhance residual memory in individuals with DAT.