Design  A retrospective analysis was performed using data from the Area Resource File. Multivariate linear regression analysis was performed to identify the variations in access to colorectal surgeons, gastroenterologists, and radiation oncologists.

Setting  All counties in the United States.

Participants  Prevalence rate of African Americans and Asian Americans within a county.

Main Outcome Measure  Rate of colorectal surgeons, gastroenterologists, and radiation oncologists.

Results  Unadjusted analysis revealed that each percentage point increase in the African American population within a county was associated with a decrease in the number of specialists within that county. Multivariate analysis also revealed a statistically significant decrease in the number of gastroenterologists (P < .001) and radiation oncologists (P < .001) with each percentage point increase in the African American population and a trend toward a decrease in colorectal surgeons within that county (P = .28). Each percentage point increase in the Asian American population was associated with a significant increase in the number of gastroenterologists (P < .001) and radiation oncologists (P < .001) with a similar trend toward an increase in the number of colorectal surgeons within that county (P = .13).

Conclusion  Increasing numbers of minority patients in counties is accompanied by a differential access to specialists. This may affect the likelihood of a patient to receive appropriate care.

Different counties in the United States have varying health care resources, the availability and use of which may vary. A recent study has implicated increased distance to point of care in counties as contributing to decreased access by minority patients and, thus, having a potential role in the disparities observed among minority groups.⁸ Findings from previous studies have shown that endoscopic colon cancer screening is low among some minority groups and is lowest among African Americans.^{6, 9-10} The increased distance traveled may serve as a deterrent to seek care farther away for what is deemed an asymptomatic condition. Therefore, this population as a whole may be less likely to undergo endoscopic screening or be diagnosed at an early stage of colorectal cancer.^{6, 11} Because endoscopy is the mainstay of diagnosis, strategies to allow early diagnosis have been proposed to reduce these disparities.^11-12 Geographic availability of endoscopists within a county may affect the willingness and feasibility of the patient to present for endoscopic screening. Without adequate availability, minority patients may continue to present with advanced colorectal disease. In addition to lower screening rates, minority patients (African Americans in particular) are also less likely to receive appropriate adjuvant therapies such as chemotherapy and radiotherapy. Zhang et al⁸ identified differences in 30-day mortality rates for colon cancer between African Americans and Asian Americans with African Americans having the higher rates. These differences may be exacerbated by limited access to providers such as radiation oncologists in the counties in which these minority patients live. In this vein, racial disparities in access may be affected by residential area and racial clustering within counties in the United States. We sought to examine the relationship between varying rates of ethnic minorities and the availability of colorectal surgeons, gastroenterologists, and radiation oncologists within counties in the United States.

METHODS

Unadjusted and multivariate analyses were performed to examine the relationships between racial ethnicity and the various indices of access to colorectal screening as determined by opportunity and the geographic availability of gastroenterologists, colorectal surgeons, or radiation oncologists within a county. These variables included the rates of each of these providers within the county. The independent variables were prevalence rates of African Americans and Asian Americans in a county.¹⁴ County-level independent variables including socioeconomic characteristics (number of privately insured and median household income) and education status (rate of population with a high school diploma) were used in the adjustment. The extent of urbanization was estimated using the rural-urban continuum code.

We used commercially available software (STATA Intercooled version 10; StataCorp; College Station, Texas). Similar to Xirasagar et al,¹⁵ we used linear regression analysis rather than logistic regression to mimic past authors in the analysis of personal level data from national surveys. We sought to assess the net effect of the proportion of specific minority groups on the opportunity to use subspecialty resources in a county for which linear regression analysis of county-level data serves best. The ecological correlations described were computed without the extra refinement of weighting by the proportion of minority groups in each county. This decision has been reaffirmed in previous research in which ecological correlations have been described as being negligible.¹⁶ The US Department of Health and Human Services uses weighted, sequential, hot-deck imputation for missing values in the data set.

RESULTS

COMMENT

Furthermore, we identified that an increasing percentage of African Americans in a given county was associated with a statistically significant decrease in the number of radiation oncologists. We, therefore, noted a decrease in the providers of both diagnostic and adjuvant therapies of colorectal cancer care. There have been demonstrable disparities reported in the literature pertaining to the geographic availability of adjuvant therapies such as radiotherapy and chemotherapy, particularly for patients presenting with stage II or III rectal cancer.¹² Growing evidence suggests that increasing the receipt of appropriate adjuvant therapies may serve to reduce cancer mortality among African Americans.¹² African American patients, however, are less likely to receive the appropriate surgery or adjuvant radiotherapy or chemotherapy even after receiving the initial referral.^23-25 Morris et al¹² postulated that in the absence of difference in insurance status, the disparity may be caused by transportation difficulties or complexities in navigating the medical system. Thus far, little has been offered in the literature to address the influence of residential geographic location on the racial disparities in access to colorectal cancer care.

Varying articles exist about the effect of segregation on health outcomes in general. Some reports suggest that African Americans and Hispanic Americans may perceive fewer barriers to care when they live in an area with a higher prevalence of people with similar ethnicity.^{6, 26} In alignment with this concept, Geronimus²⁷ postulates that a set of social networks within a segregated community may mitigate against the effects of segregation. Other articles in contradistinction lay out the negative outcomes associated with segregation including an increased all-cause mortality and differential access to subspecialty interventions.^28-29 Zhang et al⁸ identified that increasing prevalence of minority groups was associated with higher adjusted mortality.

African Americans are the most racially segregated ethnic group in the United States.^30-31 The highest rates of colorectal cancer mortality occur in inner-city communities despite the decline in overall mortality rates.¹¹ Strategies that target the appropriate use of adjuvant therapies in the counties in which African Americans live may be impeded by the sheer lack of availability of the providers in these areas. Perhaps the nonuse of diagnostic and adjuvant therapies is related to the great distances that African Americans must travel to seek these services, plausibly outside their own residential counties. This may serve as an impediment to seeking these services despite the best intentions of referring physicians and surgeons. Access to diagnostic and adjuvant therapies is central to timely screening, diagnosis, follow-up therapy, and surveillance, without which longer-term survival may never be improved and disparities never equalized.

This article is limited by its use of national administrative databases. Furthermore, the cross-sectional design does not allow a causal inference to be drawn, but in it we address the unspoken effect of racial clustering by examining the entire US population, and seek to define what role it may have in fueling disparities in colorectal cancer care in the United States.

AUTHOR INFORMATION

Accepted for Publication: November 26, 2008.

Author Contributions: Study concept and design: Hayanga, Kaiser, Chang, and Morris. Acquisition of data: Hayanga and Chang. Analysis and interpretation of data: Hayanga, Waljee, and Kaiser. Drafting of the manuscript: Hayanga and Kaiser. Critical revision of the manuscript for important intellectual content: Hayanga, Waljee, Chang, and Morris. Statistical analysis: Hayanga and Kaiser. Study supervision: Waljee, Chang, and Morris.

Financial Disclosure: None reported.