Grass pollen exposure is associated with higher hospital readmission rates in children with asthma, according to study findings published in Pediatric Allergy and Immunology.

Grass pollen is known as a risk factor for primary asthma admission and for leading to inadequate asthma control. Investigators in Australia therefore sought to evaluate the association between grass pollen and pediatric asthma readmission.

The researchers conducted a review of the Victorian Admitted Episodes Dataset from July 1997 through June 2009 to identify children 2 to 18 years of age with a principal diagnosis of asthma admitted to the hospital in Victoria, Australia. Readmission was defined as an admission within 28 days of an index admission discharge. Generalized additive models stratified by sex and age were used to evaluate associations between daily grass pollen counts, lagged and cumulative time, grass pollen season, and readmission.

Investigators identified a sample of 48,068 primary pediatric asthma admissions for analysis (39.8% involving female patients). Of these, 2152 (4.53%) were associated with a subsequent asthma readmission within 28 days of discharge. The highest mean (SD) daily readmissions occurred in children 2 to 5 years of age (0.26 [0.52]) and in male children (0.27 [0.54]). The association between mean daily readmission rates and daily pollen concentrations was similar for boys and girls in models stratified by sex.

Researchers identified days associated with grass pollen season using weather data from the Bureau of Metrology (including maximum and minimum temperatures and relative humidity) and hourly data on air pollutants (ozone and particulate matter up to 10μm) from the Environment Protection Authority (EPA) in Victoria.

The investigators found the highest mean daily readmission rates occurred during grass pollen season for all children (incidence rate ratio [IRR], 1.44; 95% CI, 1.03-2.02), and for children 2 to 5 years of age (IRR, 1.99; 95% CI, 1.26-3.14). During the pollen season, daily grass pollen concentrations ranged from 0 to 356grains/m3. Grass pollen concentrations that were not in pollen season were not included in the analysis.

Younger children with severe or poorly controlled asthma could be referred for preventive therapies before the grass pollen season, to reduce the likelihood of a repeat admission.

A nonlinear association was found between same-day grass pollen and daily readmission for children 13 to 18 years of age between 110 and 256grains/m3 (P <.01). A nonlinear association was also found between “lag 2 grass pollen” (ie, grass pollen 2 days later) and overall daily readmissions (P =.03), male children (P =.01), children 2 to 5 years of age (P =.02), and children 6 to 12 years of age (P <.001). Investigators speculated that no association existed with older children (13 to 18 years of age) because they may have had a better understanding of their triggers and the need to adhere to preventive measures. Investigators further noted that cumulative pollen values over 4 days were significantly associated with daily readmissions only for children 6 to 12 years of age.

Study limitations include the observational design, the lack of grass pollen data outside of peak pollen season, and the lack of data on individual patient viral infections, hay fever, or second-hand smoke (ie, potential modifying factors). The potential for misclassification bias was also significant, given that the model assumed all children experienced identical exposures to ambient grass pollen.

“Younger children with severe or poorly controlled asthma could be referred for preventive therapies before the grass pollen season, to reduce the likelihood of a repeat admission,” investigators concluded, adding that better asthma education might help to reduce readmissions for asthma in young children.

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

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