Airborne pollen may contribute to asthma-related ED visits

Key takeaways:

• Asthma was the primary diagnosis in 649,754 emergency visits in Texas.
• All pollen types were positively associated with numbers of emergency visits.
• Larger cities were more affected during peak pollen season.

Airborne pollen may be a major cause of asthma-related ED visits during peak pollen season, but the risk varies by location and plant composition, according to a study published in Environmental Research.

“Allergenic pollen can have meaningful effects on public health, but much less is known about how the effects of pollen vary among cities,” Daniel S. W. Katz, PhD, assistant professor in the School of Integrative Plant Science at Cornell University, told Healio.

“A clearer link between local plants and their impacts on health outcomes could provide insight into which public health and health care delivery interventions would be most effective in which places,” he said.

Methods

This study used data from ED visits in Texas between October 2015 and December 2020 from the Texas Department of State Health Services. Inpatient and outpatient visits were included where the primary diagnosis was asthma as well as the census block group of each patient based on their address if it was within 25 km of a pollen monitoring station.

Pollen data were taken from eight National Allergy Bureau (NAB) stations in Texas including: College Station, Dallas, Flower Mound, Georgetown, Houston, San Antionio A, San Antonio B and Waco.

Pollen taxa were grouped into three different types: Cupressaceae (mountain cedar/ash juniper), other trees and other pollen types such as ragweed. Researchers noted that Cupressaceae was separated in analysis due to its peak time, regional concentration and because it comprised 32% of all airborne pollen collected.

Data on viruses were collected through the National Respiratory and Enteric Virus Surveillance System and the Texas Department of State Health Services. Tests for rhinovirus, seasonal coronavirus, respiratory syncytial virus (RSV) and influenza virus were collected.

Results

During the study period, 649,754 asthma-related ED visits were reported. Among these, 177,988 were included in the analysis due to their 25 km proximity to a NAB station.

The highest average daily number of asthma-related ED visits per 1,000,000 residents were seen in young children aged younger than 5 years at 24.1 (range, 15-39.3), then school-aged children aged 5 to 17 years at 20.7 (range, 15-35) and adults at 8.1 (range, 6.9-10.44).

Seasonal patterns were observed in young children and school-aged children. For every pollen type examined, a strong seasonal pattern was observed. Cupressaceae pollen was the highest in winter, tree pollen was highest in spring and other pollen types were highest in the fall. During peak seasons, Cupressaceae and tree pollen often exceeded 1,000 pollen grains/m³, whereas other pollen was sometimes greater than 100 pollen grains/m³.

Seasonality was also seen in positive virus tests with rhinovirus, present most of the year, peaking in September; influenza through December to March; seasonal coronavirus from December to January; and RSV in December. Spikes for influenza were seen at the end of 2017 and in the spring of 2017 for rhinovirus, and some viruses exhibited meaningful differences regionally.

For young children, the high level of asthma-related ED rates of 24.1 visits per 1 million person-days were mostly linked to viruses (51.2%). Attributable risk was highest for rhinovirus (40.8%), RSV (4.2%), influenza (3.5%) and coronavirus (2.7%), whereas tree pollen (1.1%) and Cupressaceae pollen (0.9%) were lower. The total attributable risk was 53.2%.

The 20.7 visits per 1 million person-days among school-aged children showed the highest attributable risk for rhinovirus (42.1%), followed by influenza (8.3%), RSV (4.2%), seasonal coronavirus (2.4%), tree pollen (2.8%) and Cupressaceae pollen (0.7%). The total attributable risk was 60.5%.

The lower rates of 8.1 visits per 1 million person-days among adults showed the highest attributable risk for rhinovirus (18%), followed by seasonal coronavirus (6.2%), RSV (1.2%), tree pollen (2.3%) and Cupressaceae pollen (0.8%). This group had the lowest percent of total attributable risk at 30.8%.

Researchers showed that over the study period, 4,113 ED visits were attributed to pollen. The risk varied between seasons and age groups as well as between cities.

“Our study highlights the clinical importance of allergenic pollen to people with asthma. In certain cities during peak pollen season, up to 19% of asthma-related emergency department visits were attributable to allergenic pollen,” Katz said.

“Another important finding is that some cities are hit far harder by allergenic pollen than others, and this is due in part to differences in which plants grow where,” Katz continued. “Here, a single species of juniper was responsible for 9% of asthma-related emergency department visits in January, but only in the cities where it was abundant.”

Study results further show that, for example, in January, at the height of Cupressaceae pollen season, school-aged children around the San Antonio A NAB station had a higher percent of attributable risk from Cupressaceae pollen than children near the Houston station (9% vs 0.3%).

However, during March — the month with highest tree pollen concentrations — the highest attributable risk was found in Houston (18.6%) whereas the lowest was seen in Waco (7.3%). The average risk among all the cities was 11.6%.

Researchers highlighted that both viruses and pollen explained the seasonality of asthma-related ED visits in school-aged children. September visits for this age group were attributable to rhinovirus, with 52.7% occurring in Georgetown and Austin. However, peaks in early winter and spring could be attributed to both Cupressaceae and tree pollen.

“Our results show that pollen has a substantial negative effect on people’s health — and in doing so highlights the need for better approaches to dealing with airborne pollen,” Katz said. “Potential solutions include better management of allergy medications and providing accurate pollen forecasts so people can reduce their exposure.”

Katz further explained that this study shows the magnitude of the problem caused by allergenic pollen exposure and emphasized the need for better solutions to address it.

“Beyond understanding the general clinical importance of allergenic pollen to patients with asthma, health care professionals can best serve their patients by knowing their local plants and when each species is releasing allergenic pollen,” he said.

Another point Katz emphasized is a lack of accurate pollen forecasts.

“We are working on creating better models of airborne pollen that will allow people to both take allergy medications in time for them to reach full efficacy before exposure and to inform decisions about how they can reduce their own exposure to allergenic pollen (eg, closing windows, avoiding outdoor recreation during peak pollen conditions, or wearing masks),” he said. “Ultimately, knowing the connection between local plants and their health effects will allow us to leverage plant ecology to benefit public health.”