Pollen exposure linked with respiratory symptoms among infants

Researchers have found an association between pollen exposure and increased risk for respiratory symptoms even during infancy, according to a study published in European Journal of Allergy and Clinical Immunology.

The study included 401 term-born infants enrolled in the Basel-Bern Infant Lung Development cohort between Jan. 1, 2005, and Jan. 1, 2016.

Amanda Gisler, PhD candidate in public health/epidemiology at University Children’s Hospital Basel in Switzerland, and colleagues evaluated daily concentrations of tree and grass pollen, individually and combined, reported by the Swiss Federal Office of Meteorology and Climatology. Previously developed spatiotemporal models provided daily concentrations of particulate matter with an aerodynamic diameter of 2.5 µm (PM_2.5) and nitrogen dioxide (NO₂). Researchers assessed temperature and humidity as well.

Trained study nurses called the parents of these infants each week throughout the first year of their life to evaluate daytime and nighttime cough, wheezing and dyspnea based on a standardized five-category score indicating increasing symptom severity from 0 to 4.

Respiratory symptom scores were low overall, the researchers found. The mean symptom score was 0.13 (standard deviation [SD], 0.13) for daytime respiratory symptoms and 0.12 (SD, 0.14) for nighttime respiratory symptoms across all years from January through September.

Infants had daytime respiratory symptoms during an average of 3.92 (SD, 3.77) weeks and nighttime respiratory symptoms during and an average of 3.03 (SD, 3.01) weeks.

According to the researchers, there was an association between exposure to tree and grass pollen both individually and combined and respiratory symptoms during the first year of life.

During the daytime, risk ratios (RRs) per 10% pollen/m³ included 1.006 (95% CI, 1.002-1.009) for combined pollen, 1.005 (95% CI, 1.002-1.008) for tree pollen and 1.009 (95% CI, 1-1.018) for grass pollen. At night, RRs per 10% pollen/m³ included 1.003 (95% CI, 0.999-1.007) for both combined pollen and tree pollen and 1.014 (95% CI, 1.004-1.024) for grass pollen.

The researchers did not find any interaction between combined pollen and maternal atopy or the infant’s sex, although they said there was a complex crossover interaction between combined pollen and PM_2.5 (P = .002).

Although pollen had the opposite effect on respiratory symptoms depending on PM_2.5 levels, PM_2.5 did not have any main effect. Further, there were no interactions between grass and tree pollen individually or combined with NO₂, but NO₂ had a positive association with daytime respiratory symptoms (RR per µg/m³ = 1.011; 95% CI, 1.002-1.02).

Noting that their work is the first longitudinal study to show associations between risks for respiratory symptoms and pollen exposure even in healthy infants, the researchers described infancy an important window of opportunity and called for larger studies to reveal the mechanisms behind these associations.