Alberta Residents Research Articles

Chronic Disease Score as a covariate of multiple regression models

Purpose Derive the Chronic Disease Score (CDS) as a covariate of the multiple regression models for comorbidity adjustment with automated pharmacy data in Alberta, Canada. Methods Different types of medications prescribed during 2001/2 for the treatment and management of chronic conditions were obtained from Alberta Blue Cross (ABC) claims database. The medications were clustered into 25 therapeutic classes to indicate the presence of a chronic illness based on the criteria proposed by Clark et al in 1995. The study population was composed of all Alberta residents aged 65 or over who were registered with the Alberta Health Care Insurance Plan (AHCIP) continuously from 2001/2 to 2002/3. Individuals who terminated the registry before March 31, 2003 were included if they had been admitted to hospitals in 2002/3. Individuals were excluded if they had been diagnosed with any malignancy, tuberculosis or HIV during 2001/2 and 2002/3. Medications used in the direct treatment of these diseases are provided by other health insurance agencies instead of ABC. Hospitalization rate in 2002/3 was derived from AHCIP databases. Logistic regression models were utilized to estimate CDS scores. The CDS developed by Clark et al was replicated with Alberta Data. Its validity was compared with that of the proposed CDS. Results Records for 216,724 seniors were used to estimate the empirical weights for calculating CDS. Odds ratios for hospitalization from predicted CDS increased with each percentile group. The risk of hospitalization increased 12-fold for persons with a predicted score in the 90th–100th percentile over those in the 0 th –10th percentile. It was higher than those devised from any of the 3 CDS scores with cost or utilization weights. Conclusion CDS can be generally used as a combined covariate to adjust morbidity rates for different populations. To improve the validity of the adjustment, the weights of CDS should be estimated using the morbidity (hospitalization for this study) rate itself as the dependent variable of the regression model.

Predictors of Colorectal Cancer Screening: A Comparison of Men and Women

New Canadian guidelines recommend screening average-risk adults to reduce mortality from colorectal cancer, the second most common cause of cancer death among Canadians. The present study examined the self-reported prevalence of colorectal cancer testing and sex-specific predictors of having had a fecal occult blood (FOB) test for screening, among a cohort of Alberta residents aged 50 to 69 years. Subjects (n=5009) enrolled in a geographically based cohort study completed a Health and Lifestyle Questionnaire between October 2000 and June 2002 that ascertained their colorectal cancer detection practices, as well as demographic and other health and lifestyle characteristics. Patterns of FOB testing, and sigmoidoscopy or colonoscopy, were similar for men and women. The majority of subjects (83.3%) reported no first-degree family history of colorectal cancer or bowel conditions, and they were considered to be at average risk. Few average-risk subjects reported having a screening FOB test within the past two years (7.7% [95% CI 6.7% to 8.7%] of subjects aged 50 to 59 years and 12.5% [95% CI 10.9% to 14.3%] of subjects aged 60 to 69 years). In men, the strongest predictors of having a screening FOB test in the past two years were a recent history of prostate-specific antigen testing and educational attainment. Among women, the strongest predictors were a recent history of having had a Pap test, a recent mammogram, employment status and educational attainment. Screening for colorectal cancer in average-risk adults was infrequent in this sample and lagged behind screening for other cancers. Screening of average-risk adults occurred primarily in people already accessing the health care system, suggesting that public education programs will be required to increase screening rates.

Evaluating institutionalization by comparing the use of health services before and after admission to a long-term-care facility.

Despite concern over increased health services utilization with population aging, few studies describe health services utilization by long-term-care (LTC) residents. An investigation was designed to compare health services use before and after LTC admission. Comprehensive 1988 to 1999 data for all LTC residents (N = 47,510) in Alberta, Canada, were obtained. Utilization comparisons involved equal pre/post timeframes. Only non-hospital physician services increased post-LTC admission. Home care was not provided after admission (51% had been recipients). Hospital and ambulatory services use declined, with these patterns stable for 5 years pre- and post-LTC admission. When hospital or ambulatory care was sought by LTC residents, they were not disadvantaged in the type or scope of care as compared to the care received prior to LTC admission. These findings should raise interest in the services provided by LTC facilities and the outcomes of long-term, facility-based care. LTC services could be beneficial for people with advanced age and dependency.

EFFICACY AND SAFETY OF LOW-DOSE FLUTICASONE PROPIONATE COMPARED WITH ZAFIRLUKAST IN PATIENTS WITH PERSISTENT ASTHMA

Sin DD, Man SFP. Arch Intern Med . 2002;162:1591–1595 To determine if inhaled corticosteroid (IC) therapy prescribed after discharge from the emergency department (ED) prevents relapse of asthma exacerbations. Twelve hundred ninety-three residents of Alberta, Canada, who were enrolled in a government drug plan and visited an ED for asthma exacerbations between April 1, 1997, and March 31, 1999. The study cohort was identified using the Ambulatory Care Classification System database. Patients 5 to 60 years of age who had at least 1 ED visit for asthma were included in the cohort if they were enrolled in the government-sponsored drug plan. …

LOW-DOSE INHALED CORTICOSTEROID THERAPY AND RISK OF EMERGENCY DEPARTMENT VISITS FOR ASTHMA

Sin DD, Man SFP. Arch Intern Med. 2002;162:1591–1595To determine if inhaled corticosteroid (IC) therapy prescribed after discharge from the emergency department (ED) prevents relapse of asthma exacerbations.Twelve hundred ninety-three residents of Alberta, Canada, who were enrolled in a government drug plan and visited an ED for asthma exacerbations between April 1, 1997, and March 31, 1999.The study cohort was identified using the Ambulatory Care Classification System database. Patients 5 to 60 years of age who had at least 1 ED visit for asthma were included in the cohort if they were enrolled in the government-sponsored drug plan. The cohort was followed from the time of the first identified ED visit to the date of a subsequent ED visit. Information regarding prescribed asthma medications was obtained through the Alberta Blue Cross database. The study population was stratified into nonusers and users of IC as well as into low- (<500 μg/day beclomethasone diproprionate or equivalent per day), medium- (501–1000 μg/day), and high-dose (>1000 μg/day) users. Rates of subsequent ED visits for asthma were compared between the IC users and nonusers and between the low-, medium-, and high-dose groups using the Cox proportional hazard regression.Six hundred fifty-eight (50.9%) of the cohort were not prescribed IC. Of those who were prescribed IC, 241 (18.6%) received low-dose, 96 (7.4%) received medium-dose, and 122 (9.4%) received high-dose IC. Corticosteroid users were older and were more likely to have used other asthma medications during the first 100 days of follow-up than nonusers. Inhaled corticosteroid use was associated with a decreased risk (relative risk [RR]: 0.64; 95% confidence interval [CI]: 0.52–0.79) of a subsequent ED visit. After adjusting for age, sex, use of other asthma medications, comorbidity and hospitalization, IC users still had a significantly reduced risk of a repeat ED visit (RR: 0.55; 95% CI: 0.44–0.69). Patients in all 3 dose categories had significantly reduced risks of repeat ED visit (low-dose: RR: 0.52; 95% CI: 0.39–0.68; medium-dose: RR: 0.51; 95% CI 0.39–0.68; high-dose: RR: 0.67; 95% CI: 0.47–0.94). However, medium- and high-dose IC did not reduce the rate of repeat ED visits to any greater extent than did low-dose IC.In this cohort with recent ED visits for asthma, IC reduce the risk of subsequent ED visits. The results suggest that this risk reduction is similar across all 3 dose groups and thus high-dose IC may not afford any greater protection than low-dose IC.Although ICs have been shown to improve lung function and reduce symptoms, the effect on ED visits and hospitalizations has been more difficult to ascertain because of the relative rarity of these outcomes as compared with symptom-based outcomes. The authors circumvented this issue by selecting a cohort of patients who had visited an ED for asthma thereby enriching the study population for those with more severe disease. This study underscores the significant role ICs play in preventing ED visits for asthma and suggests that the next step is to define the optimal dose range so that the risk:benefit ratio can be minimized.

Research Note: Describing Canada's Residential Continuing Care Population through an Analysis of a National Mortality Dataset and a Provincial Hospital Dataset

ABSTRACTWhile there are 157,000 designated continuing care (CC) beds in Canada – beds that are only used by a rather distinct group of individuals – no comprehensive description of the CC resident population exists. An analysis of 1974–1997 Statistics Canada mortality data and 1992/93–1996/97 Alberta hospital utilization data was undertaken to provide a description of one segment of this population, those at the end of life. Statistics Canada data indicate that only a small (&lt;3%) proportion of deaths take place each year in CC facilities, with these persons 84.5 years of age on average, and most often female (62.5%), widowed (61.9%), and Canadian born (61.8%). The primary cause of death/diagnosis varied considerably, as it did for CC residents in Alberta who were transferred to acute care hospitals before dying there. The average hospital stay for transferred persons was 14.0 days in length, with these hospitalizations normally characterized by few diagnostic tests or treatments (mean=0.9).

Near-Fatal Asthma: A Population-Based Study of Risk Factors

Background The study of near-fatal asthma (NFA) may provide a means to further our understanding of fatal asthma. Studies of NFA often are derived from a single ICU rather than from a defined population. We therefore aimed to identify factors distinguishing NFA patients (cases) from those persons treated in an emergency department (ED) [ED control subjects] and in the community (community control subjects [CCs]). Methods This was a population-based case-control study conducted over 20 months of 45 NFA patients (age range, 5 to 50 years), 197 ED control subjects treated in an ED, and 303 CCs, all of whom were residents of Alberta. Results The age distribution was similar between NFA patients and control subjects, with the majority being < 22 years of age (NFA patients, 68.9%; ED control subjects, 71.3%; CCs, 60.7%). Those patients with NFA were significantly more likely to have received a diagnosis before 5 years of age (66.6%), compared to ED control subjects (39.6%) and CCs (28.7%). The NFA group was significantly more likely to report moderate-to-severe disease and more frequent symptoms than the other groups. Therapy with bronchodilators was used most frequently by the NFA group compared to the ED control subjects and CCs (p < 0.001), as was therapy with inhaled steroids (p < 0.001) and oral steroids (p < 0.001). NFA patients had higher scores for vulnerability and were most likely to admit to stress as an asthma trigger. All groups had high exposure to cigarette smoke and pets. Conclusion NFA patients have many modifiable risk factors and many similarities to ED control subjects and CCs with asthma. General measures to improve asthma control and awareness of risks are required in all groups. The study of near-fatal asthma (NFA) may provide a means to further our understanding of fatal asthma. Studies of NFA often are derived from a single ICU rather than from a defined population. We therefore aimed to identify factors distinguishing NFA patients (cases) from those persons treated in an emergency department (ED) [ED control subjects] and in the community (community control subjects [CCs]). This was a population-based case-control study conducted over 20 months of 45 NFA patients (age range, 5 to 50 years), 197 ED control subjects treated in an ED, and 303 CCs, all of whom were residents of Alberta. The age distribution was similar between NFA patients and control subjects, with the majority being < 22 years of age (NFA patients, 68.9%; ED control subjects, 71.3%; CCs, 60.7%). Those patients with NFA were significantly more likely to have received a diagnosis before 5 years of age (66.6%), compared to ED control subjects (39.6%) and CCs (28.7%). The NFA group was significantly more likely to report moderate-to-severe disease and more frequent symptoms than the other groups. Therapy with bronchodilators was used most frequently by the NFA group compared to the ED control subjects and CCs (p < 0.001), as was therapy with inhaled steroids (p < 0.001) and oral steroids (p < 0.001). NFA patients had higher scores for vulnerability and were most likely to admit to stress as an asthma trigger. All groups had high exposure to cigarette smoke and pets. NFA patients have many modifiable risk factors and many similarities to ED control subjects and CCs with asthma. General measures to improve asthma control and awareness of risks are required in all groups.

Regionalization and Hospital Utilization: Alberta 1991/2–1996/7

Background In February 1994 Alberta Health announced a three-year business plan for the radical restructuring of the health care system in Alberta. The business plan outlined large reductions in funding for acute hospital care spending and the establishment of 17 Regional Health Authorities (RHAs). Objectives The objectives of this study are to describe for the period 1991/2 to 1996/7: 1) Trends in overall acute hospital utilization by Alberta residents and residents of each of the 17 RHAs. 2) Trends in the provision of acute hospital services by each of the 17 RHAs and the Alberta Cancer Board. 3) Trends in the transfer of patients between RHAs. Results Between 1991/2 and 1996/7, the age-sex standardized separation rate, the age-sex standardized average length of stay, and age-sex standardized hospital days rate for Alberta residents fell by 25.6%, 18.7%, and 39.5% respectively. The age-standardized hospital days rate fell in all 17 RHAs. The total number of separations (Alberta residents and non-residents) from Alberta acute care facilities fell by 19.6% while the average care intensity for all separations from Alberta acute care facilities rose by 8.7%. The ratio of the highest to lowest average RHA care intensity remained between 1.7 and 1.9 during the study period. RHA self-sufficiency indices increased dramatically in one RHA and remained largely unchanged in the remaining RHAs. RHA import indices decreased for most RHAs. Conclusions Large reductions in the use of acute hospital services have occurred in Alberta during the period of major health care restructuring. Further research is needed to examine shifts in services to other sectors and to assess the impact of these reductions on patient outcomes.

Is primary CNS lymphoma really becoming more common? A population-based study of incidence, clinicopathological features and outcomes in Alberta from 1975 to 1996

The incidence of primary CNS lymphoma (PCNSL) is believed to be increasing in immunocompetent patients but this may not be universally true. The objective of this study was to determine in a population if the incidence of PCNSL is increasing, if the histologic subtypes are changing, and to describe the clinicopathologic and outcome characteristics of PCNSL. We identified all Alberta residents with a histologic diagnosis of PCNSL from 1 January 1975 to 31 December 1996 using the Alberta Cancer Registry. Annual age-standardized incidence rates (ASIR), clinicopathologic and outcome characteristics were determined. There were 50 immunocompetent PCNSL patients; the median age was 64 and 30 were male. Their median survival was 10.15 months. Histology was available for review in 37 (74%) patients: 19 (51%) were diffuse large cell, 16 (43%) were immunoblastic and 2 (5%) were unclassifiable malignant lymphomas. The ASIR ranged from 0.178-1.631/10(6) and no change in ASIR was found (test for trend, P = 0.26) for gender or age. The ASIR of malignant gliomas did not change either but increased for all other non-Hodgkin's lymphoma (94.95-138.7610(6); test for trend, P = 0.0001) The number of brain biopsies increased from 1979-1985 (test for trend, P < 0.0001) but remained stable from 1986-1996 (test for trend, P = 0.99). Unlike several other populations, PCNSL is not becoming significantly more common in Alberta. If this difference is real (i.e., not due to differences in cancer registry coding practices etc.) comparisons between Albertans and other populations in whom the incidence is rising may provide clues regarding the etiology of PCNSL.

Potential for community relocation among residents of Alberta's psychiatric facilities: a needs assessment.

To identify the proportion of residents in Alberta's psychiatric hospitals who would be relocatable to community-based alternatives to care if appropriate programs were made available. A Survey of a representative sample of residents in all psychiatric hospitals and care centres was undertaken, excluding patients in specialized programs for forensic psychiatry, brain injury, and substance abuse. Findings indicate that 11% of institutionalized patients could be considered good candidates for relocation to community-based alternative care. A further 35% were considered to have potential for relocation provided an intensive and complex array of services was first made available. Results support a phased-in approach to hospital downsizing and the need for considerable transitional funding. Because hospital downsizing is unlikely to save dollars, at least in the short term, reforms must remain guided by humanitarian motivations to improve quality of life for persons with severe and persistent mental illnesses.

Spouses of incest offenders: Coaddictive tendencies and dysfunctional etiologies

Abstract A study of spouses of incest offenders was conducted to discover if (a) these women had significantly more severe coaddictive tendencies than a matched group of controls, (b) whether spouses played a supportive role in encouraging offender's behavior, and (c) whether incest offenders and spouses of incest offenders had similar dysfunctional etiologies. Three samples were selected from among long-time residents of Central Alberta: 132 incest offenders, 155 spouses of incest offenders, and a control group of 100 women. Instruments used to assess various qualities of these groups included the Abuse Survey, the Coaddictive Inventory, and the Coaddictive Consequence Survey. Results supported all three experimental questions, that is, spouses demonstrated severe coaddictive tendencies, often played a supportive role in hiding or encouraging the offender's behavior, and both incest offenders and spouses experienced a wide variety of physical, emotional, and sexual abuse during childhood. These and other...

Province-Based Study of Neurologic Disability of Children Weighing 500 Through 1249 Grams at Birth in Relation to Neonatal Cerebral Ultrasound Findings

Adverse neurodevelopmental outcome in premature infants is more common in the presence of certain ultrasonographically detectable intracranial lesions. Present nomenclature and classifications of parenchymal changes in preterm infants of varying gestations have led to some confusion. Descriptive definitions may be clinically useful. Regionalized perinatal and neonatal care enables population-based studies of these lesions and subsequent outcomes. Two- to 3-year outcomes of neonates weighing 500 through 1249 g born in Alberta to Alberta residents during 1987 through 1990 were reviewed in relation to neonatal cerebral ultrasound lesions. Odds ratios and confidence limits for disability were calculated. Of 960 live births in this weight group, 669 (70%) survived to 1 year adjusted age; 646 (96.6%) were assessed at follow-up, and 80 (12.4%) of these were disabled: cerebral palsy, 8.7%; vision loss, 2.9%; hearing loss, 1.3%; epilepsy, 0.6%; mental retardation, 4.8%; more than one disability per child, 3.6%; and projected dependent disability, 1.4%. Lesions considered to be predictive of disability on ultrasound (excluding germinal layer hemorrhage) were found in 79 (11.8%), parenchymal lesions in 63 (9.4%) of 1-year survivors: intraventricular hemorrhage (IVH) (n = 59), persistent or transient cerebral ventriculomegaly (n = 50), persistent or transient intraparenchymal periventricular echodensity (n = 29), and cystic periventricular leukomalacia (n = 7). All lesions except isolated IVH were associated with adverse outcome; 37% of disabled children, 61% of multiply disabled children, and all children projected to become dependently disabled had parenchymal lesions with or without IVH. Triple lesions of IVH, cerebral ventriculomegaly, and intraparenchymal periventricular echodensity gave an odds ratio for disability of 50. Transient lesions had significant risk. This province-based study provides a descriptive scheme of serial neonatal cerebral ultrasound lesions and outcome considered useful for clinicians caring for newborns of lowest gestational ages. The overall incidence of parenchymal lesions was lower than frequently reported. Combinations of lesions were linked to increased incidence, complexity, and severity of childhood disability.

Province-Based Study of Neurologic Disability Among Survivors Weighing 500 Through 1249 Grams at Birth

As the mortality of children weighing 500 through 1249 g at birth decreases, the published rates of neurologic disability among survivors have caused concern. Outcome information from a province-based study in which perinatal/neonatal regional care is well developed and includes high-risk identification, early referral, organized transport, and outreach education, provides data from a Canadian source for comparison with epidemiologic reports. Neurologic disability rates among 2- to 3-year-old survivors weighing 500 through 1249 g at birth is provided based on all live births/neonatal survivors/1-year survivors born in Alberta, Canada to Alberta residents in 1990. Corrected survival to 1-year was 163 of 229 or 71% of live births of the total group weighing 500 through 1249 g. Of 168 live births, 143 or 85% weighing 750 through 1249 g, free from lethal anomalies, survived. Based on 1-year survival, disability rates were: cerebral palsy, 67/1000; vision loss (acuity in the best seeing eye after correction, < 20/60), 12/1000; neurosensory hearing loss (loss of > or = 30 dB binaurally), 12/1000; and trainable/profound mental retardation, 18/1000. No survivor had a convulsive disorder. No vision loss or mental retardation as defined by this study occurred in survivors of > or = 750 g. All children with cerebral palsy were or were projected to become ambulatory. Neurologic disability among small preterm surviving infants can occur less frequently than suggested by published reports. We believe this provincial study supports the value of well developed regional perinatal programs.

Hazardous material loading to municipal landfills in resource-based communities

Landfills in rural, resource-based communities are receiving unknown quantities of potentially hazardous materials, including household hazardous wastes (HHHW) and industrial, commercial, and institutional (ICI) wastes in self-hauled and collection vehicle loads. Rural generation and disposal rates are expected to be higher than in urban areas.The research program was conducted in a resource-based community consisting of a town of about 5500 residents and the surrounding rural area with an equal number of residents in Alberta. The research objective was to determine the weight fraction of hazardous materials in the refuse through physical sampling of the waste stream at the community landfill. Over a 1-year period (1991), large collection vehicle loads and self-hauled private and ICI loads from the town and the rural area were sampled during 1 week in each season using a two-staged systematic random sampling design to measure the average weight fraction and variation by season and by type of load. The results show the annual average weight fraction of hazardous materials to be 6.7% with a 95% confidence interval of 4.0% to 9.4%. Seasonal differences are apparent, but are not significant. Self-hauled ICI and rural wastes tend to contain higher percentages of potentially hazardous materials, but the variation is also higher so the values are not significantly different from those from the town. The detected materials consist mainly of oily wastes (debris, oil containers, and vehicle oil filters), other automotive products, and paints. As a result, the hazardous material content of rural community refuse appears to be substantially higher than the 0.3% to 1.0% reported for HHHW in urban refuse streams. While the rural composition suggests that vehicle and home maintenance contribute some of the difference, this study also shows that ICI wastes and self-hauled loads contribute noticeable quantities of potentially hazardous materials. The results suggest that it is essential for rural communities to consider waste management alternatives for potentially hazardous materials because rural waste streams contain significantly higher percentages and because rural landfills are often not designed to as high a standard as large urban facilities. Key words: household hazardous waste, ICI waste, waste stream analysis, rural landfills, refuse waste stream.

Family history of ovarian cancer patients: a case-control study.

In order to obtain a more correct estimate of cancer incidence in relatives of cases with ovarian cancer and relatives of age-matched controls, information was obtained on family size, date of birth and death, and cancer history. The average total number of first degree (parents and siblings) and some second degree (uncles and aunts) relatives for cases (15.03) and controls (15.22) is very similar. Of all the relatives 33% were Alberta residents or decreased in Alberta after 1966 so they could be checked in the population based Alberta Cancer Registry. There was a 14% level of error in the information provided, 9% for first degree relatives and 25% for uncles and aunts. The errors included missed malignancies, benign lesions quoted as malignancies, incorrect cancer site and inaccurate dates of birth, diagnosis or death. Results were compared between the relatives of cases and controls using either all relatives or only Alberta residents. For the Alberta residents, expected numbers of malignancies were calculated by age/sex-specific person/years and age/sex-specific incidence rates. The number of relatives with ovarian cancer is significantly higher in cases than in controls in both data sets, but shows a limited relative risk of 2.61 (95% confidence limits 1.12-1.59). Clustering of cases is exceptional, only one patient out of 197 had two relatives with ovarian cancer and this was a case with a larger than average total number of relatives. In conclusion, although there is a significantly higher incidence of ovarian cancer in the family history of cases than of controls, it is not very common and only nine out of 197 cases (4.6%) presented with such background.

"Föhn illness" and human biometeorology in the chinook area of Canada.

Literature on the nature and possible causes of ‘fohn illness’ is reviewed. Seven physiological and psychological aspects of human well-being were solicited from 1828 residents of southern Alberta by telephone interview. Data were evaluated to determine if well-being was weather related. Meteorological parameters included eight 48-h weather types, temperature, humidity, wind and pressure. The expected increase in fohn illness symptoms during the frequent warm chinook and decrease at times of cold non-chinook weather were not present. However, with the cool chinook (temperature slightly below freezing) many people claimed additional irritability and, to a lesser extent, more pain in their joints, headaches and nervousness. Several adverse symptoms were positively correlated with wind velocity. However, no widespread ‘chinook illness’ comparable to the fohn illness was found.

Trends in the incidence of cancer of the female breast and reproductive tract in Alberta, 1953 to 1977

A log-linear model was used to separate age, secular, and cohort trends in the incidence of cancer of the breast, ovary, corpus uteri, cervix uteri, vagina, and vulva in female residents in Alberta over the period 1953 to 1977. The age trends are similar for each cancer site increasing sharply in the premenopausal period and then leveling off. In the case of breast cancer, a point of inflection at the menopause (Clemmesen's hook) persists. A gradually increasing secular trends in incidence was evident for all sites except cervix uteri, the incidence of which declined after 1960. Cyclical cohort trends were found for cancers of the breast, ovary, and corpus uteri, inversely correlated with early fertility. The cohort trends for cervix uteri, vagina, and vulva increased sharply for cohorts born after 1940.

The Optimal Savings Question: An Alberta Perspective

This paper examines one question of fundamental economic significance to the Alberta Heritage Savings Trust Fund debate, namely: how much should a province whose income depends upon the extraction and sale of a non-renewable resource in finite supply save for the benefit of future generations of provincial residents when the number of these residents is dependent upon the volume of induced migration? To explore this optimal savings question requires one to consider both the constraints under which the provincial economy operates as well as the objectives it seems desirable to pursue. The revenues placed in the Fund are derived from the development and extraction of petroleum resources, and more particularly conventional oil and natural gas, which are limited in supply. Although exploration and development activity can expand the volume of proven resources of conventional oil and natural gas, it is clear that existing rates of extraction will, if continued, eventually exhaust the supply of these resources that can profitably be extracted at any given technological and cost-price configuration. Assuming that alternative sources of energy continue to be available to the world economy, and therefore that the real price of energy does not escalate faster than the rate of extraction within Alberta declines, the timestream of Alberta's non-renewable resource revenues must eventually decline in real terms as her conventional oil and natural gas reserves are depleted. The existence of substantial heavy oil and tar sands deposits within the province does not alter this picture, since the resource rents per unit of output that the development and extraction of these deposits will generate are most unlikely to be as large as those for proven reserves of conventional oil and natural gas, given any reasonable forecast of the evolution of technological knowledge and associated cost-price relationships. As a result of the existence of substantial non-renewable resource revenues, Albertans have come to expect their provincial government to provide them, on a per capita basis, with a high level of public goods and services in relationship to the direct and indirect taxes which they pay. Without these non-renewable resource revenues, the provincial government would have to impose a substantial increase in taxation in order to provide these goods and services to Alberta residents. This tax increase would lead inevitably to a reduction in the ability of Alberta residents to purchase private goods and services in the market place. From this point

MOSQUITOES AND HUMAN DISEASE IN CANADA

AbstractIn the early 19th century, malaria was indigenous in Upper Canada (Ontario), but indigenous infection has not been seen in Canada since about 1909. For many years mosquitoes were regarded principally as harmless pests of man and domestic animals until the recognition of a number of mosquito-borne viruses. At present, mosquitoes in Canada are known to be involved in the maintenance or spread of at least seven arboviruses. One of these viruses, western equine encephalomyelitis, occurs in epidemics in man and horses at irregular intervals in the western provinces. The extent to which the other arboviruses might cause disease in man or domestic animals in Canada is unknown at present but California encephalitis virus infection rates can be high in human residents of central Saskatchewan, central Alberta, and southern British Columbia. On the basis of observations made in the United States, St. Louis encephalitis virus could pose a threat to public health in Canada whereas the Cache Valley virus might involve livestock. Even if man and livestock are not involved at present in epidemics of disease due to these viruses, the presence of the viruses and their vectors should be of concern. Epidemics could arise either from amplification of causal viruses already present in indigenous foci or by amplification of viruses from new enzootic foci recently established by extension of the geographic ranges of the viruses. Evidence indicating which category each of the known viruses in Saskatchewan belongs to is briefly reviewed. Japanese B encephalitis virus has not yet been seen in Canada but the environmental prerequisites for an epidemic or epizootic due to this virus appear to be present and awaiting the arrival of the virus.