Geographical variations in the prevalence of atopic sensitization in six study sites across Canada.

BACKGROUND: Geographical variations in atopic sensitization in Canada have not been described previously. This study used the standardized protocol of the European Community Respiratory Health Survey-1 (ECRHS-1) to investigate the distribution and predictors of atopic sensitization in six sites across Canada and to compare the results with some ECRHS-1 centers. METHODS: Adults aged 20-44 years in six study sites across Canada underwent allergy skin testing using 14 allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae) cat, cockroach, grasses (Timothy grass, Kentucky grass), molds (Cladosporium herbarium, Alternaria alternata, Aspergillus fumigatus, Penicillium), trees (tree mix, birch, Olea europea), and common ragweed. RESULTS: The overall prevalence of atopy (skin test over 0 mm to any allergen) was 62.7%. There was significant geographical variation in the prevalence of atopy in the six study sites (lowest 55.6% [95% C.I.51.3-59.9] in Prince Edward Island, highest 66.0 [61.7-70.3] in Montreal) and of sensitization to each of the allergens tested even after adjustment for confounders. When the first eight of the nine allergens in the ECRHS were used to estimate the prevalence of atopic sensitization, the prevalence of atopy in Canada was 57% compared with 35.2% overall for centers in the ECRHS. The prevalence of atopy in Vancouver (57% [52.3-61.8]) was close to that of Portland, Oregon (52.1% [46.2-58.0]). CONCLUSION: There was a significant variation in atopic sensitization among different study sites across Canada. The prevalence of atopic sensitization is relatively high in Canada compared with sites in the ECRHS and this may, in part, account for the high prevalence of asthma and asthma symptoms in Canada.

Prevalence of asthma symptoms among adults aged 20-44 years in Canada.

BACKGROUND: Reported prevalence rates of asthma vary within and between countries around the world. These differences suggest environmental factors in addition to genetic factors in the cause of the disease and may provide clues for preventive strategies. We examined the variability of asthma-related symptoms and medication use among adults in 6 sites across Canada (Vancouver, Winnipeg, Hamilton, Montreal, Halifax and Prince Edward Island) and compared our findings with those from sites that had participated in a recent European survey. METHODS: We used the same sampling strategy and standardized questionnaire as those used in the European Community Respiratory Health Survey (ECRHS). The 6 Canadian sites were selected to represent different environments with respect to climate, air pollution and occupational exposure. Community-based samples of 3000 to 4000 people aged 20-44 years were randomly selected in each site. Subjects were asked to complete the questionnaire by mail between March 1993 and November 1994. Prevalence rates (and 95% confidence intervals [CIs]) of asthma symptoms, self-reported asthma attacks and use of asthma medication were compared across the Canadian sites and with sites that had participated in the ECRHS. RESULTS: The overall response rate of those selected to receive the questionnaire was 86.5% (range 74.5%-92.8%). The prevalence rates of most asthma symptoms varied significantly among the Canadian sites. For instance, 21.9% (Montreal) to 30.4% (Halifax) of the men and 24.0% (Vancouver) to 35.2% (Halifax) of the women reported wheezing in the year before the survey. Depending on the site, 4.4% to 6.3% of the men and 5.2% to 9.5% of the women reported an asthma attack in the last year, and 4.0% to 6.1% of the men and 4.9% to 9.7% of the women were currently using asthma medication. Prevalence rates of symptoms, asthma attacks and medication use did not change with age, but they were higher among women than among men. Compared with the results from the ECRHS sites, those from the Canadian sites were among the highest. INTERPRETATION: Significant variation in the prevalence of asthma symptoms, asthma attacks and use of asthma medication between Canadian sites and international sites suggests environmental influences. Different combinations of factors in different sites may be responsible for the high prevalence rates and should be the subject of further research to guide clinical management and public health intervention.

Evaluating screening tests for dementia and cognitive impairment in a heterogeneous population in the presence of verification bias.

This article reviews two potentially serious sources of error in the evaluation of screening tests, namely, verification bias and the influence of demographic covariates. It demonstrates how to deal with these problems statistically. Verification bias arises when not all subjects receive a definitive diagnosis following a screening test. If only a small proportion of those who screen negative are sent for diagnosis, the calculated test sensitivity is an overestimate and the calculated specificity an underestimate. The methodology outlined in this article may be extended to psychological and medical screening tests in general.

Blood recipient notification for hepatitis C in Prince Edward Island.

BACKGROUND: Two of the major risk factors for hepatitis C are injection drug use and receipt of blood or blood products. Many patients are unaware that they have received transfusions. In 1998 Prince Edward Island conducted a province-wide look-back notification program to notify patients who had received transfusions in PEI between Jan. 1, 1984, and June 1, 1990. The authors present the results of the notification program. METHODS: A registry for recipients of blood and blood products was created from the province's Red Cross blood bank records. The registry data were linked with Vital Statistics data to determine death status and with Health Registration data to determine residence status of recipients (in PEI or moved out of province). All identified recipients with a current PEI mailing address were sent a letter recommending hepatitis C virus (HCV) testing. Laboratory records were checked to determine HCV test results. RESULTS: The registry contained data for 6086 recipients of blood or blood products during the look-back period; 51.1% (3109/6086) had died by the time of notification. Of the remainder, 18.4% (549/2977) were not directly notified because they had moved out of province, had refused delivery of the notification letter or had died recently, or because identifying information was missing from the blood bank records. Of the recipients who were notified 80.4% (1953/2428) underwent testing, and 2.2% (43/1953) were found to be HCV positive. Most of these (58.1% [25/43]) had undergone testing before notification. The HCV positivity rate differed significantly between recipients tested before notification and those tested after notification (9.9% v. 1.1%, p < 0.001). HCV-positive recipients were more likely than other notified recipients to have had multiple transfusions (39.5% v. 9.5%, p < 0.001). INTERPRETATION: Before notification 4.1% of PEI recipients had undergone HCV testing. After notification 91.2% of PEI recipients were identified as tested, dead or moved out of province. The notification program resulted in the identification of the majority of PEI's transfusion-related cases of hepatitis C.

Screening for nutritional risk among community-dwelling elderly on Prince Edward Island.

The purpose of this survey was to estimate the prevalence of nutritional risk among a group of community-dwelling older persons on Prince Edward Island, aged 70 years and over, and to examine the relationships between health-related factors and nutritional risk. Subjects (n = 215) were interviewed as part of the 1996 Canadian Study of Health and Aging. The prevalence of nutritional risk, as measured by the DETERMINE checklist, in PEI seniors was 37.1% (95% CI = 36.3, 37.9). The prevalence was estimated at 47% after adjusting for the sensitivity and specificity of the checklist. Only pain was a significant predictor of the presence or absence of nutritional risk (logistic regression, p = 0.05). The only predictor to discriminate between the three categories of no nutritional risk, moderate risk, and high risk was depression (Kruskal-Wallis, p = 0.035). Several limitations were identified with the use of the DETERMINE checklist.

Epidemiological associations between Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae antibody titers and lung lesions in Prince Edward Island swine herds.

A survey of anteroventral (AV) lung lesions, pleuritis and serology for Mycoplasma hyopneumoniae (MH) and Actinobacillus pleuropneumoniae (AP) was conducted on a minimum of 25 slaughter hogs from each of 18 randomly sampled Prince Edward Island farms (producing over 1,000 market hogs per year). The data were analyzed to evaluate the potential role of these two agents as risk factors for the two conditions, using crude and multivariable techniques, as well as individual and herd data. Anteroventral lung lesions were present in 50.5% of hogs at slaughter, and pleuritis was present in 15.4% of the hogs. Least squares multivariable regression was used to analyze the simultaneous ability of MH, AP and MH/AP interaction to predict the herd prevalence of AV lung lesions. Only MH was associated with AV lung lesions (p = 0.035). In spite of this statistical significance, MH accounted for only 53% of the herd variation in prevalence of lung lesions (R2 = 0.529). As well, some herds maintained very low levels of lung lesions despite moderate (up to 30%) prevalence of MH. Discrepancies between the analytic techniques suggested herd-level factors play an important role in the development of lung lesions. Pleuritis did not appear to be associated with either of the agents studied (p = 0.478).

A serological survey of leptospirosis in Prince Edward Island swine herds and its association with infertility.

A serological survey was undertaken to determine the prevalence of leptospirosis, and to investigate associations between leptospiral antibody titers, and herd measures of reproduction. Production records and leptospirosis serology were analyzed for 25 slaughter hogs from each of eleven randomly sampled farrow-finish operations on Prince Edward Island. The effect of selected leptospiral serovars on nonproductive sow days per parity (NPSD/P) and the proportion of pigs born dead was evaluated. The four most common serovars to which antibodies were detected were Leptospira icterohaemorrhagiae, L. bratislava, L. autumnalis and L. pomona, with respective prevalences of 57.1%, 35.1%, 3.4% and 1.5% of PEI slaughter hogs. None of these serovars was associated with increased frequency of stillbirths (p greater than 0.05). However, farms with a higher prevalence of L. bratislava antibody titers tended to have more infertility, as measured by NPSD/P (r = 0.738, p = 0.036 with Bonferroni adjustment). Also, farms with L. pomona antibody titers had higher NPSD/P than farms without L. pomona antibody titers (p = 0.0008 with Bonferroni adjustment). There was no association between NPSD/P and antibodies to either L. autumnalis or L. icterohaemorrhagiae (p greater than 0.05).

Epidemiological approach to the association between economic efficiency and productivity on swine farms in Prince Edward Island.

Regression analysis was used to determine the ability of a number of biological parameters to predict economic efficiency. Detailed feed, financial, and production records were maintained by a random sample of eighteen Prince Edward Island (PEI) swine producers (each producing over 1000 market hogs per year). Relative economic efficiency of the operations was measured using return to management and labor (RML). Of the routinely monitored biological parameters, RML on PEI farrow-finish operations was best predicted (R2 = 64.8%) by: marketed per square meter per year (p = 0.008) and marketed per sow per year (p = 0.096). Regression of fixed costs revealed that biological parameters had limited ability to predict fixed costs per hog on farrow-finish operations (R2 = 30.7%). The only parameter contributing to the prediction of the fixed cost component of RML was feeder hog density (p = 0.077). The variable cost component of RML on farrow-finish operations was predicted (R2 = 94.3%) by feed cost per kg gain (p = 0.000), and marketed per sow per year (p = 0.044). The routinely recorded biological parameters on feeder farms had only limited ability to predict RML in this study (R2 = 43.7%). The only parameter of any importance was marketed per square meter per year (p = 0.106). Prediction of the fixed cost component of RML on feeder farms (R2 = 67.4%) was best realized by measuring feeder hog density (p = 0.045). The variable cost component of RML on feeder farms was reasonably well predicted (R2 = 74.7%) by feed cost per kg gain (p = 0.012). Although this parameter is difficult to monitor from records currently maintained on most farms, it points out the need to monitor feed consumption on swine farms.

A survey of biological productivity of Prince Edward Island swine herds.

Sow and feeder pig productivity were measured on a random sample of 32 Prince Edward Island swine farms (each producing over 1000 market hogs per year). Productivity parameters could be arranged in a hierarchy, with the highest level on farrow-finish operations represented by pigs weaned per sow per year. The 17 farrow-finish farms in this study averaged 19.6 (+/- 2.2 SD) pigs weaned per sow per year. Large variation between farms was observed with a range from 16.2 to 24.9 pigs weaned per sow per year. The major opportunities for improving productivity, as compared to reviewed targets, lie in reducing the average weaning age, reducing preweaning mortality, and reducing non-productive sow days per parity. The 14 feeder operations were characterized by 0.58 +/- 0.07 kg average daily gain. Average daily gain was negatively correlated with mortality (r = -0.662, p = 0.010), suggesting that herds that achieved a high rate of gain also had lower mortality.