Association of asthma exacerbations with paper mulberry (Broussenetia papyrifera) pollen in Islamabad: An observational study

Abstract

Background: Although the role of airborne plant pollen in causing allergic rhinitis has been established, the association of concentrations of paper mulberry (Broussenetia papyrifera) pollens in the air and incidence of asthma exacerbations has not, despite an observed increase in the number of asthma patients attending physician clinics and hospital Accident and Emergency (A&E) Departments during the paper mulberry pollen season. We aimed to assess the association between paper mulberry pollen concentrations (typically peaking in March each year) and asthma exacerbations in the city of Islamabad.

Methods: We used three approaches to investigate the correlation of paper mulberry pollen concentration with asthma exacerbations: A retrospective analysis of historical records (2000-2019) of asthma exacerbations of patients from the Allergy and Asthma Institute, Pakistan (n = 284), an analysis of daily nebulisations in patients attending the A&E Department of the Pakistan Institute of Medical Sciences (March 2020 to July 2021), a prospective peak expiratory flow rate (PEFR) diary from participants (n = 40) with or without asthma and with or without paper mulberry sensitisation. We examined associations between pollen data and asthma exacerbations using Pearson correlation.

Results: We found a strong positive correlation between mean paper mulberry pollen counts and clinical records of asthma exacerbations in patients sensitised to paper mulberry (Pearson correlation coefficient (r) = 0.86; P < 0.001), but not in non-sensitised patients (r = 0.32; P = 0.3). There was a moderate positive correlation between monthly nebulisation counts and pollen counts (r = 0.56; P = 0.03), and a strong negative correlation between percent predicted PEFR and pollen counts in sensitised asthma patients (r = -0.72, P < 0.001). However, these correlations were of low magnitude in the non-sensitised asthma (r = -0.16; P < 0.001) and sensitised non-asthma (r = -0.28; P < 0.001) groups.

Conclusions: Our three approaches to analysis all showed an association between high paper mulberry pollen concentration in Islamabad and asthma exacerbations. Predicting pollen peaks could enable alerts and mobilise strategies to proactively manage these peaks of asthma exacerbations.

Figure 1

Comparison of mean asthma exacerbations and mean paper mulberry pollen counts for sensitised and non-sensitised patients. Panel A. Patients with paper mulberry sensitation. Panel B. Patients without paper mulberry sensitization. Both groups reported the months of asthma exacerbations retrospectively at their first clinic visit (previous history) and at subsequent clinic visits (recent asthma exacerbations). Furthermore, the month of a physician-confirmed asthma exacerbation and paper mulberry pollen counts were documented. All data were normalised.

Figure 2

Comparison of daily numbers of nebulisations, daily pollen concentration and daily new confirmed COVID-19 infections. All data were collected from 1 March 2020 to 30 July 2021. The blue lines show the new infections on a day, the green line show the nebulisation number at A&E at PIMS, while the red line shows the pollen count on that day. Missing values are shown by gaps in the line.

Figure 3

Comparison of mean percentage of expected PEFR with daily paper mulberry pollen counts. The solid thick black line shows the mean percentage of expected PEFR, while the thin dashed line shows the normalized daily paper mulberry count. Breaks in the PEFR data show times when none of the participants of a group provided data.

Figure 4

Pearson’s correlation coefficients between percent expected PEFR of individual asthma patients and paper mulberry pollen counts. Individual correlations between percent expected PEFR and paper mulberry pollen counts were calculated and are presented as box plots (box = 25^th to 75^th centile, thick black line = median, lower whiskers = up to 24^th centile, upper whiskers = above 75^th centile, dots = outliers).