Do Conocarpus erectus airborne pollen grains exacerbate autumnal thunderstorm asthma attacks in Ahvaz, Iran?

Abstract

A disastrous outbreak of thunderstorm-induced asthma attacks posed a major public health threat in Ahvaz, Iran in autumn of 2013 (>15,000 referrals to hospital emergency rooms and pulmonary clinics). City officials claimed that promoting factors included acid rain, particulate matter, ozone, and polycyclic aromatic hydrocarbon compounds (PAHS) could lead to this phenomenon. After these potential causes were rejected by careful research, the next possible cause that this study addresses is a potential link of the asthma attacks to airborne pollen grains and fungal spores. In order to sample these parameters, a Hirst-type volumetric spore sampler was used, which was installed on the rooftop of the sampling site. Sampling was done during two six-month periods to characterize the regional bioaerosol. The first period included the autumn (September 22 to December 20 of 2016) and winter seasons (December 21 of 2016 to March 19 of 2017), while the second period included the following autumn (September 23 to December 21 of 2017) and winter seasons (December 22 of 2017 to March 20 of 2018). In both studied periods, airborne weed pollen grains, especially Amaranthaceae sp., were by far the greatest contributor to total airborne pollen grain concentrations (50.45%, 3757 pollen grains/m3 and 52.12%, 2392 pollen grains/m3, respectively). Among fungal spores, Cladosporium had the highest concentrations (75.29%, 258677 spores/m3 and 80.33%, 247693 spores/m3, respectively). Findings also showed that concentrations of airborne pollen grains were higher in autumn seasons (6361 and 4167 pollen grains/m3, respectively) in comparison with winter seasons (1085 and 423 pollen grains/m3, respectively), while the concentrations of fungal spores were enhanced in winter seasons (189216 and 160962 spores/m3, respectively) versus autumn seasons (154377 and 147377 spores/m3, respectively). Fungal spores exhibited a uniform distribution during the entire study period, but airborne pollen grains were significantly higher in autumn seasons. The numbers of referrals associated with thunderstorm asthma attacks decreased drastically after implementing Conocarpus erectus tree pruning activities. We concluded that the autumnal thunderstorm asthma attacks in Ahvaz might be triggered by a combination of bio-allergens (fungal spores and airborne pollen grains such as from Conocarpus erectus) and high levels of air pollutants from industrial activity. The results of this work suggest controlling bio-allergen levels by preventive measures such as tree pruning, weed removal, and emasculating urban green infrastructures before the flowering season.