CDA Essentials 2018 • Volume 5 • Issue 1

34 | 2018 | Issue 1 S upporting Y our P ractice Cycle 2 of the CHMS (2009–2011) provides an opportunity to examine the validity of the exposure variable used in our 2012 paper. Specifically, Cycle 2 includes estimates of fluoride presence in urine samples for a random subsample of respondents, aged 3–79 years. Although fluoride in urine is from all sources, not only tap water, 6 the sensitivity of urinary fluoride to variations in community water fluoridation under stable conditions (at least 1 year) has been demonstrated. 7 The objective of this study was to examine the validity of the geographic measure of fluoridation in the CHMS (based on data collection site), by examining its association with fluoride estimates from urine samples. A secondary objective was to use home postal codes to identify respondents’ community of residence and to assess whether fluoridation status assigned based on that more precise geographic location is more closely associated with urinary fluoride estimates than fluoridation status based on CHMS data collection site. Findings will inform options for monitoring fluoridation status in populations, which is of relevance to dental public health researchers, as well as options for policy and practice for those involved in public health surveillance. Methods Data Source The data source is Cycle 2 (2009–2011) of Statistics Canada’s CHMS. 8 Cycle 2 was a cross-sectional, nationally representative survey that included a clinical examination administered in a mobile clinic, as well as a household interview. The target population was people aged 3–79 years, living in all provinces and territories; sample exclusions represented less than 4% of the target population. 8 This study focuses on the environmental urine subsample ( n = 2563). Multistage sampling was used, in the following manner. 8 The sampling frame from the Labour Force Survey was used to create 257 geographic areas, each containing at least 10,000 people. These sites were stratified into 5 regions (British Columbia [including Whitehorse], Prairies [including Yellowknife], Ontario, Quebec and Atlantic provinces). Within each region, sites were sorted by census metropolitan area status and population size, and 18 sites were systematically selected. This process ensured inclusion of both census metropolitan areas and non-census metropolitan areas, and both larger and smaller populations. Within each site, stratified sampling by age group was performed, using the 2006 census as a sampling frame. The mobile clinic (where data collection took place) was set up at a designated location within each of the 18 sites. Maximum travel distance from a site was set at 50 km for urban areas and 100 km for rural areas. 8 The household response rate was 75.9%; of those participants, 90.5% provided questionnaire data, and, of those, 81.7% reported to the mobile clinic. Of the mobile clinic sample ( n = 6393), 2,623 people were randomly selected for the environmental urine subsample; of these, 2,563 (97.7%) provided a valid spot urine sample. 8 Urine was collected using a 120-mL specimen container with an aliquot volume of 1.0-mL (3–5 year olds) or 1.8-mL (6–79 year olds). Analysis was carried out at the Centre de toxicology du Québec of l’Institut national de santé publique du Québec (accredited under ISO 17025) using standardized operating procedures. 9 Fluoride was analyzed using an Orion pH meter with fluoride ion selective electrode (Orion Research Inc.). 10 The limit of detection, 20 μg/L, was estimated based on the United States Environmental Protection Agency protocol (EPA 40 CFR 136). 9 Analysis First, the fluoridation status of each data collection site was assigned based on publicly available information from such sources as municipal websites, water quality reports, media items and websites of anti- fluoridation groups. Corroboration across multiple sources was sought. Although it was more difficult to find information for some sites than for others, it was possible to discern fluoridation status with reasonable certainty for all sites. The assessment based on publicly available sources was confirmed through correspondence with the Office of the Chief Dental Officer, Public Health Agency of Canada, and there were no instances of contradictory information. Individual survey respondents were classified as fluoridated or non-fluoridated based on this site- level information. Fluoridated was defined according to current national guidelines, 7 which, in practice, correspond to a range of 0.5–0.8 mg/L. Non- fluoridated means no fluoride is added to the water supply, and natural fluoride levels are below 0.5 mg/L. Second, mean urinary fluoride concentration for fluoridated and non-fluoridated groups was compared, both as crude weight per volume of urine (μg fluoride/L urine) and adjusted for urinary creatinine (e.g., μg fluoride/g creatinine). Urinary creatinine is commonly used for adjustment of spot urine samples because its 24-h production and excretion rates are relatively constant, 9 and can thus help adjust for the effects of urinary dilution, some differences in renal function, and lean body mass. 9