City vs province: How does asthma differ with address?

Asthma manifests differently between patients from urban and rural areas, likely due in part to differing environments, according to a recent study presented at the virtual International Congress 2020 of the European Respiratory Society (ERS 2020).

“Multiple variables, such as environmental exposure, are involved in the aetiology of asthma, which may be different depending on whether it’s a rural or urban environment,” the researchers said.

In this study, the researchers sought to determine whether or not such a difference in environment affected the disease profile of asthma by conducting a descriptive epidemiologic investigation on 516 people who lived in a rural area and by comparing them to 522 city-dwellers. An initial detection questionnaire was administered to the participants to identify those with respiratory symptoms.

In the rural and urban subgroups, majority of the participants (65 percent and 70 percent, respectively) showed no signs of respiratory issues. However, bronchitis was detected in 20 percent and 18 percent, while evidence of asthma was reported in 15 percent and 11 percent, respectively. Asthmatic participants were asked to answer a second survey, which sought to characterize the condition. [ERS 2020, abstract 1310]

The researchers found important differences between the environmental subgroups. Those who lived in urban areas were significantly more likely to have had severe respiratory infections during childhood than their rural counterparts (40 percent vs 18.5 percent; p=0.011). Allergic rhinitis was also more prevalent in city-dwellers (64.0 percent vs 40.0 percent; p=0.011).

Asthma symptoms likewise differed between groups. Morning coughs were more than thrice as common in urban vs rural participants (68.0 percent vs 18.5 percent; p<0.001), and morning expectorations also occurred at more than twice the rate in the urban subgroup (44.0 percent vs 21.5 percent; p=0.01). Day and/or night coughs were five times more frequent in city-dwellers, too (46.0 percent vs 9.2 percent; p<0.001).

Notably, wheezing (58.5 percent vs 58.0 percent) and exertional dyspnoea (55.4 percent vs 54.0 percent) were the only symptoms that were more common in the rural subgroup, but neither reached statistical significance.

It’s possible that the discrepancy in symptom profile could be explained by differences in exposure. For example, coughs (p=0.002), nasal congestion (p=0.007), and eye congestion (p=0.006) attributable to inhaled irritants were more common among urban participants, while dyspnoea due to the same exposure was more prevalent among those in rural areas (p<0.001).

Environmental pollution also emerged as an important contributor to asthma symptoms, especially in the urban subgroup, where it accounted for a significantly higher burden of coughs (p=0.015) and nasal (p<0.001) and eye (p=0.002) congestion. In rural participants, environmental pollution was a strong driver of dyspnoea (p<0.001).

“In both populations, there [was] a greater number of symptoms in contact with irritants and environmental pollutants,” the researchers said, however noting that “only individuals in the urban population showed a higher prevalence of symptoms in contact with allergens.”

“The inhabitants of urban areas seem to have an exacerbating asthmatic phenotype, mainly related to allergens,” they said. “Future studies should aim to study the environmental-pollution relationship in these patients.”