Given the disadvantages rural Americans face in the broader healthcare system, the first question regarding the impact of asthma in rural communities is what is the relative prevalence of asthma in rural versus urban and suburban areas. There is surprisingly little data addressing this question, most of it international. In the International Study of Asthma and Allergies in Childhood Phase III (ISAAC III), 13.8% of 13-14 year olds and 10.8% of 6-7 year olds worldwide carried a diagnosis of asthma. The prevalence is somewhat higher in North America, Western Europe, and Australia compared to Africa, Latin America, and Asia, although this difference has narrowed since ISAAC I. While this data, when viewed by country and region, suggests that asthma is more prevalent in more populous and industrialized areas, the ISAAC studies generally had one to a few centers per country, always located in cities, and thus it is difficult to estimate worldwide asthma prevalence in urban versus rural areas from this data.7
Several international studies are available, however, that compare the prevalence of asthma in urban and adjacent rural areas, with all finding lower asthma prevalence in rural areas. Solé et al.
analyzed ISAAC III data of 13-14 year olds from two Brazilian centers, Caruaru and Santa Maria, and found a significantly higher rate of wheezing ever, wheezing in the past 12 months, or lifetime asthma diagnosis in the children living in urban areas compared to those from rural areas.8
Yemaneberhan et al.
conducted a household survey in Ethiopia of 9844 people from the urban, pre-industrial city of Jimma and 3032 people from three nearby rural communities. While the observed prevalence rates were low overall, rates differed significantly for rural and urban groups for self-reported asthma (3.6% urban, 1.3% rural) and wheeze in the prior year (3.7% urban, 1.2% rural).9
Keeley et al.
examined reversible airways obstruction (which they defined as a 15% decrease in peak expiratory flow with exercise correctable with salbutamol) in urban versus rural children in Zimbabwe. The rate of reversible airways obstruction by this definition was 5.8% and 3.1% in the two urban populations, statistically significantly higher than the 0.1% rate observed in the rural population.10
Korzyrskyj and Becker conducted a mail survey in Manitoba, Canada in 2002-2003 of households with 7 year old children, and found that families reported asthma in 14% of urban children compared to 8% of children from northern and 10% of children from southern rural Manitoba. It should be noted that this survey was limited by a poor response rate.11
There is a paucity of studies comparing asthma prevalence in rural communities in the US to similar populations in nearby cities. In a study of Iowa schoolchildren, Chrischilles et al.
conducted a mail survey using ISAAC questions of parents of 3090 children ages 6-14 in two rural Iowa counties. They found an overall prevalence of wheeze in the past 12 months of 19.1%, and a prevalence of doctor-diagnosed asthma of 12.4%. In multivariate analysis controlling for age, sex, and county, children who lived on farms versus those who lived in town in the same counties were less likely to ever wheeze (odds ratio [OR] 0.71, 95% confidence interval [CI] 0.58-0.87) or to experience wheeze in the last 12 months (OR 0.77, 95% CI 0.6-0.98).12
Perry et al.
examined asthma prevalence in two school districts in the Delta region of Arkansas, an impoverished, rural and medically-underserved region of the United States. The majority of students were African American (97%) and had government-issued medical insurance (73%). Of the students completing the survey, which had an 81% response rate, 268/964 (28%) were considered at risk for asthma by previous physician diagnosis or a validated asthma algorithm diagnosis. The at-risk population was highly symptomatic and the majority (79%) had evidence of persistent asthma with 82% reporting activity limitations, 59% reporting frequent nocturnal symptoms, and 49% either hospitalized or treated in the emergency room for asthma in the preceding 2 years. These findings not only suggest asthma prevalence higher than national rates, but also reveal significant evidence of uncontrolled asthma in this rural, impoverished, predominately African American population.13
Most of the large American asthma prevalence studies (American Lung Association Trends in Asthma Morbidity and Mortality 2007, National Asthma Survey 2003, National Survey of Children's Health, Hospital Discharge Data System, National Hospital Discharge Survey, National Health Interview Survey) whose datasets could be analyzed to address national urban versus rural asthma prevalence in the United States unfortunately have not been utilized to assess rural asthma burden.14,15
In a report by Jackson et al.
at the Rural Health Research Center at the University of Washington that analyzed Behavioral Risk Factor Surveillance System data for 2003, these investigators found a lifetime prevalence of asthma in urban American counties of 12% versus 11% for rural counties (n=264,648 and p<0.001).16
From the available data reviewed above, asthma appears to be less prevalent in rural than in urban international areas, and less convincingly so, in the rural US compared to urban areas of the US. Rural US populations with a large proportion of minority or low income residents seem to the contrary to have an exceptionally high prevalence of asthma. Furthermore, residents of the United States have a higher burden of asthma than residents of most areas of the developing world regardless of urban or rural residence.