Air pollution, weather changes may exacerbate allergic rhinitis symptoms
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Key takeaways:
- The strongest effects of particulate matter and nitrogen dioxide on outpatient visits for allergic rhinitis occurred on lag day 0.
- Each 10 µg/m3 increase in concentrations of sulfur dioxide was associated with a 7.69% increase in daily outpatient visits for allergic rhinitis.
- There was a negative correlation between risk for daily outpatient visits for allergic rhinitis and temperatures below 16.4°C.
Increased concentrations of air pollutants and meteorological changes were associated with numbers of outpatient visits for allergic rhinitis, according to a letter published in Allergy.
Although most previous studies of these associations have been conducted in single cities in medium latitudes, this study focused on three cities in a low-latitude region, Xin Luo, of the departments of allergy and otolaryngology-head and neck surgery, Third Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China, and colleagues wrote.
The researchers examined data from 178,692 daily outpatient visits for allergic rhinitis in the Guangdong-Hong Kong-Macao Greater Bay Area in China from 2014 to 2019 in addition to air pollution and meteorological data.
By calculating the main and lag effects of air pollutants and meteorological factors on these visits, the researchers found that particulate matter at 2.5 µm (PM2.5) and 10 µm (PM10) and nitrogen dioxide (NO2) had the strongest effects on daily outpatient visits for allergic rhinitis at lag day 0. Sulfur dioxide (SO2) had its strongest effects on these visits on lag day 2, and the strongest effects for maximum 8-hour moving average ozone (O3_8h) were at lag day 3.
Cumulatively, SO2, NO2 and O3_8h had their strongest effects at lag days 0 to 5, whereas PM2.5 and PM10 had their strongest effects at lag days 0 to 6.
Each 10 µg/m3 increase in SO2 concentration was associated with a 7.69% (95% CI, 1.04%-14.78%) increase in daily outpatient visits for allergic rhinitis. The same increase in NO2 concentration was associated with a 2.43% increase (95% CI, 1.31%-3.56%) in visits.
Similarly, each 10 µg/m3 increase in PM2.5 was associated with a 1.84% increase (95% CI, 0.67%-3.02%). For PM10, it was a 1.55% increase (95% CI, 1.04%-2.05%), and for O3_8h, it was 0.34% (95% CI, 0.1%-0.58%).
By age group, older adults were more sensitive to PM2.5 and PM10, and adolescents and younger adults were more sensitive to SO2, NO2 and O3_8h.
There was a nearly S-shaped exposure-response relationship curve for windspeed that rose sharply at concentrations below 4.5 µg/m3 and above 8 µg/m3 and flattened in between those points, the researchers continued.
Further, the researchers found a steep slope in the entire range of the exposure-response relationship curve of relative humidity and a nearly U-shaped curve with no statistical significance for sunshine duration.
The researchers also found negative correlations between risk for daily visits and temperature when it was below 16.4°C. Males and females both experienced sensitivity to low temperatures, although adolescents and younger adults were more vulnerable than children and older adults (RR = 1.57; 95% CI, 1.11-2.21).
Windless conditions in extreme weather seemed to have a greater effect on children, adolescents and younger adults, but these differences did not reach statistical significance, the researchers wrote. Compared with males, females were more susceptible to windless (RR = 1.11; 95% CI, 1.02-1.21) and windy (RR = 1.75; 95% CI, 1.01-3.01) conditions.
Females (RR = 1.69; 95% CI, 1.03-2.76) and adolescents and younger adults (RR = 1.74; 95% CI, 1.06-2.87) experienced statistically significant effects due to dry weather. Finally, the researchers wrote, all groups except older adults were slightly sensitive to sunny or cloudy weather.
Perspective
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The findings are interesting and support the hypothesis that climate change and related air pollution are drivers of the allergy epidemic. The study also is significant as it looked at a large number of endpoints, 178,000 outpatient visits for allergic rhinitis and examined three different locations.
The association of meteorologic factors (including temperature, humidity and particulate matter concentration) with allergic rhinitis visits suggests a causal relationship.
It would have been nice if the investigators had also examined an unrelated reason for outpatient visits to serve as a negative control. Also, when conducting these types of studies, it would be helpful to indicate the criteria by which allergic rhinitis was diagnosed and truly shown to be exacerbated at the time of the outpatient visit.
Future research should aim to replicate these findings and provide a mechanistic assessment of the effect of these environmental factors on allergic rhinitis. Although the examined meteorological and air pollution factors are undoubtably influenced by climate change, it will be important to show a more direct role for climate change.
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