Air pollution and general practitioner access and utilization: a population based study in Sarnia, 'Chemical Valley,' Ontario

Research based on recent conceptualizations of health that recognize socioeconomic and environmental determinants in Canada shows that significant health disparities continue to persist, despite a health care system based on the premise of universal and equitable access [1, 2]. Regional health care expenditures in Ontario are also associated with toxic pollution output [3, 4]. Such associations between the physical environment and health have highlighted the need to study the compounding impacts of environmental and socioeconomic stressors with a focus on context specific environmental health and health care issues.

Analyses of primary health care outcomes under the assumption of universal access have revealed that access and utilization depend on a host of individual, social and environmental factors. For example, physician use is determined by both individual and neighbourhood income in addition to educational attainment [5, 6]. Dunlop et al. [7] found that lower socioeconomic status (SES) was associated with increased use of primary care and lower rates of specialist service utilization, whereas health needs as measured by perceived health status and health condition predicted utilization across the board. Finkelstein [8] found that health care expenditures were related to income, but this association disappeared after adjusting for health status. Curtis and MacMinn [9] indicated that inequities related to lower levels of income and education in Canada actually grew between 1978 and 2003, while health status remained strongly associated with health care utilization. However, SES inequities in utilization appeared attenuated after initial contact with the primary care system. Among studies that did not consider temporality, but rather focused on spatiality, efforts have included controlling for health service environments as different among Public Health Units [10], and both system- and individual- related barriers within neighbourhoods [11].

Birch et al. [12] argued that health care resource allocation should be based on the needs of a particular community rather than presenting patients, who in practicality form the basis for funding to a particular service provider. This stems from provider inability to determine the needs of those who do not present themselves as patients, which is a problem reflected in the geography of health care literature concerned with the spatial organization of health services. Geographic analysis of health care draws attention to the complexity of population needs in health service access and utilization [13]. The argument is that the relationships between individual, population and neighbourhood characteristics that determine need in a particular context (e.g., demographics, SES, mobility, ethnicity, pollution, etc.) need to be examined in order to understand health care issues. Equitable access to health care cannot be meaningfully discussed without considering needs [14].

Research on health care outcomes with explicit reference to the physical environment is most often conducted at the level of neighbourhood or intra-urban scales to capture adequate resolution of spatial variability [15, 16]. Previous studies have established relationships between neighbourhood and population characteristics that amplify environmental health impacts, but to our knowledge no studies have examined the relationship between health care and air quality directly. However, existing literature indicates that people exposed to higher levels of air pollution are particularly vulnerable to the effects of inequitable access to primary health care [17]. Access to primary care helps prevent illness and death, and is also more highly associated with equitable distribution of health in populations than specialty care [18]. Gwynn and Thurston [19] suggest that disparate access to health care may increase susceptibility to the effects of air pollution. In a Canadian context, this is of particular interest since the Canada Health Act implicitly assumes that care is available to those who are in need, but individual providers have historically been trusted to allocate resources according to federal objectives [12]. Local health care providers are faced with resource restraints that can make it difficult to meet federal objectives, and in this study we seek to further understand how the distribution of air pollution is associated with consumption of health care in Sarnia, Chemical Valley, Ontario [20].

Study Context

The City of Sarnia has a population of 71,419 and covers approximately 800 km²[21]. The Sarnia area is called 'Chemical Valley' as it is home to more than 40 per cent of all chemical processing facilities in Canada. Sarnia is also located within the government designated St. Clair River Area Of Concern (AOC), which among 16 other areas in Canada was declared in further need of health investigations relating to impacts of environmental pollution [22]. The region is also subject to significant outputs of vehicular exhaust due to the Canada-US international crossing at Bluewater Bridge, and transnational air and water pollution from Ohio, Illinois and Michigan. The Ontario Medical Association [4] estimated that Sarnia and the surrounding Lambton County suffered 100 premature deaths, 270 hospital admissions, 920 emergency visits and 471 700 minor illness days due to air pollution in 2005 alone. Fung and colleagues [20] showed that rates of hospitalization were significantly higher in Sarnia than Windsor and London, two nearby cities in Southwestern Ontario. Furthermore, a study focused on the Aamjiwnaang First Nation's reserve, which is surrounded by Chemical Valley (Figure 1), reported a sex ratio of 2:1 in favour of females and attributed this anomaly to accumulative effects of pollution [23, 24]. This background information calls for the need to examine the relationship between air pollution and health care utilization at the community level. The findings will provide guidance to local level health promotion and preventive care deficiencies with a focus on areas with poor air quality.

We use a combination of spatial, environmental, and survey data to generate and test the hypothesis that relationships between air pollution and determinants of health, access and utilization of general practitioners (GP) do exist in Sarnia, Ontario. Residents of Sarnia took part in a community health study in 2005. A stratified random sampling procedure was used to select respondents from each census tract. The survey was conducted by Canadian Viewpoint Ltd, a survey company in Toronto, Ontario (http://www.canview.com) using a computer assisted telephone interview system and introduced as a general health survey. The sample represented approximately 1% of the Sarnia population, yielding a total of 804 respondents with a response rate of 62%. This sample size was determined to be sufficiently large for the number of variables included in the analyses [25]. The study was approved by the Social Sciences Research Ethics Board at The University of Western Ontario.

Analysis

Binary logistic regression models for the dependant variables were built in which each consecutive, conceptually grouped, block of variables were entered into a stepwise regression algorithm (SES, health and behaviour, community context, and pollution health effects) following forced entry of a priori variables. The a priori variables were chosen because of their influence as demonstrated in previous studies and included age, sex, family doctor, chronic disease and mental health in the GP use model [41] and income, age, sex, unmet health care needs in past 12 months and self rated health [11, 42] in the GP access model. The variables that made a significant contribution to the model at the entry of each block were retained and included in the next block. As suggested by Hosmer and Lemeshow a less stringent significance level of 0.15 for inclusion was utilized to ensure variables with coefficients different from zero were included [43].

Based on our study objectives, we examined if burdens of air pollution were borne by residents of Sarnia who were also at a disadvantage with respect to health care access. Therefore, a priori and other significant independent variables remaining in the final models for GP use and access were forced into regression models that assessed the impacts of the monitored pollutants. Power transformations were applied to several of the continuous variables for the regression analysis as their distributions were skewed (Figure 2). To evaluate the combined impact of pollutants each respondent was subsequently ranked based on estimated exposure to NO₂ and SO₂, the results of which were in turn summed and ranked to assign an overall exposure rank to individual respondents (1-804) [44]. We split the sample into tertiles of low, medium and high rank in order to compare the determinants of health care access and utilization in spatially representable sub-samples (Figure 1). The number of sub-samples was limited to three because of sample size restrictions and the number of variables included in the analysis. All analyses were carried out with SPSS 17, PASS 11 and ArcGIS 10.0.

The study found that multiple dimensions of health along with environmental, socioeconomic, demographic, and health service spatiality predicted GP access and utilization in Sarnia. The importance of differentiating access and utilization, and furthermore taking a closer look at how they interact is exemplified in a high exposure environment. Within the context of compromised environmental quality, our findings demonstrate that neighbourhoods, individual and environmental characteristics can interact to predict access and utilization of health care. Besides the apparent impact of access to regular care on community satisfaction, our analysis revealed that the a priori, SES, health care needs and other health related variables were significantly associated with GP access. These results confirm findings from previous studies in Canada and abroad [48]. For instance, the findings here support the OMA's report [4] on the increased cost of health care due to air pollution in the Sarnia region. The results demonstrate that there are significant and specific impacts of different pollutants and their spatial distributions on primary care access and utilization.

A previous study in Sarnia found that high annoyance scores were significantly related to both NO₂ and SO₂ levels [35]. Other studies have found associations between NO₂, cardiac autonomic dysfunction and increased blood pressure, which are also symptoms of stress and can lead to cardiovascular disease [49, 50]. NO₂ can also increase the risk of respiratory tract infections through interaction with the immune system and SO₂ contributes to respiratory problems for both healthy subjects and those with pulmonary disease [51]. Increased likelihood of GP use from smoking cigarettes was attenuated by NO₂ and BTEX, and the effect became insignificant with SO₂ in the model. Therefore, we suggest that NO₂, BTEX and SO₂ in Chemical valley increase health care utilization because of their effects on respiratory and cardiovascular diseases prominently featured in the area [20]. Thompson et al. [52] reported that daily fluctuations in benzene concentrations predicted acute asthma emergency admissions of children in Belfast, Northern Ireland, but our analysis showed no direct significant relationship between BTEX and our outcomes. This may be because the predicted distribution of these compounds when taken together does not reveal their individual impacts since their modes of dispersion and the way people respond to them differ. Most health effects associated with VOCs are observed over longer periods of time.

Our results suggest that low SES and stress enhanced by odour annoyance may be compounding health care demands, possibly due to increased susceptibility to adverse pollution impacts (e.g., compromised immune system) [53]. This 'double burden of deprivation' has been identified in studies conducted in Worcester, U.S.A., and Montreal, Canada [15, 54]. We observed that the low income only predicted access significantly within the medium and high exposure zones and not the low exposure area. This finding signifies a worrisome interaction between burdens of social and environmental stress, and access to primary health care services. We also found that high exposure ranked respondents were more likely than low ranked respondents to lack GP access if renting, which provides further support for low SES being a barrier to health care.

The role of odour annoyance as a stressor in Sarnia is consistent with work by Shusterman et al. [55] who found that odour mediated mechanisms and annoyance contribute to how people judge and cope with air quality, and furthermore provide important diagnostic information in appraising the potential threats to health and well-being. Research on beliefs regarding toxicity of environmental pollution suggests that "if environments smell bad, they're probably damaging to health" [56] or at the very least, they may reinforce annoyance. Consistent with earlier studies [57], we found females were more likely to report high odour annoyance than their male counter parts. This could be because of gender differences in cognitive and affective processes [57].

Negative perceptions about the environmental health of one's neighbourhood can influence health outcomes along with predisposing determinants of health [58, 59]. Consequently, perceived personal susceptibility and severity of health threats are modified by psychosocial factors, which thereafter can influence compliance with medical recommendations and perceived benefits of preventive action [60]. Benefits of access to regular care are not only preventive, but also associated with the responsibility placed on health care providers to inform and educate their patients about hazards of air pollution [61]. It is therefore particularly concerning to find that residents in Sarnia who live in high exposure areas spend more time travelling and waiting for GP consultations. This may be due to primary care providers in Sarnia locating their practices in less polluted areas, thus leaving those in highly polluted areas to travel long distances to seek care. Further research is required to determine the apparent challenges of delivering primary health care services to these areas and their populations.

Although levels of estimated exposure for respondents in the current study were within provincial guidelines, our monitoring methods were not able to capture the impact of individual release events of airborne toxins or "bad air days"; they are not uncommon and are occasionally accompanied by warning sirens and emergency response guides that demand individual coping mechanisms [62]. We can assume that residents at risk from chronic exposure are the same residents at most risk from these events. Residential areas within the high rank zone of Figure 1 provides target areas for improving health care delivery as population characteristics in this zone predicted inequitable access and coincide with high NO₂ and SO₂ concentrations that increased the likelihood of utilizing services.

There are a few limitations to this analysis that are worth noting. We note that our conceptualization of access related to a source of regular care at the time of the study and did not account for barriers to acquiring a family doctor or the fact that some people do not attempt to find regular care. Our measure of access did not include alternative sources of care such as walk-in clinics, Telehealth Ontario (free telephone consultation with a registered nurse) and nurse practitioners, and these providers arguably represent important points of access for certain deprived populations identified in this study. A study that looked at access to family physicians in Southwestern Ontario found that of the 9.1% of the population that did not have regular care, 55% used walk-in clinics and 13% used emergency rooms as their source of care [63]. The study was also limited by lacking longitudinal measures of health and SES as the study used a cross-sectional design. O'Neill et al. [64] suggest studies on air pollution that include SES measures consider how they change through the course of life. They also propose that exposure assessment include the effect of daily movement, which our study design did not permit. Furthermore, we found that our model predicting health care utilization was relatively weak, but there were nonetheless significant associations with air pollution that have potential implications for policy.

The aim of the study was to examine the relationship between spatially sensitive measures of air pollution and general practitioner access and utilization in a high exposure environment. Our results provide further support to the pursuit of better access to regular primary care in communities faced with environmental challenges. The Ontario Medical Association projects that increased numbers of premature deaths, hospital admissions and emergency visits due to air pollution in Lambton County, which includes Sarnia and smaller communities in the surrounding area, will increase to $6 million in lost productivity and $8 million in additional health care costs by 2026. We conclude that some of these costs can be avoided by ensuring equitable access to primary care for residents most severely affected by air pollution.