The perfect storm: the best conditions for making pollinic patients’ symptoms worse

During spring time, one of the best types of weather conditions favouring pollinosis symptoms appears to be dry storms. Recently, we had the opportunity of studying one of these. It was a wellremembered dry storm for pollinic patients, who referred to it as ‘the perfect storm’, i.e. the ideal weather conditions to make their symptoms as bad as they could remember. The study was carried out in Salamanca (Spain), a city with a continental climate where anthesis peak of most allergenic plants occurs from mid-May to mid-June. The study period was 29 May 2002 to 4 June 2002. To register the aggravation of pollinosis, we reviewed the medical records of patients who attended the three major emergency departments of the city during the study period for pollinosis. The pollen count was made with a volumetric spore trap (Burkard Manufacturing Co. Ltd, England). The slides corresponding to the period of study were scanned transversally at 2-h intervals. Meteorological recordings were obtained from the National Meteorological Institute. Finally, the relationship between variables was carried out by means of Pearson’s R, seeking the best possible adjustment by linear or polynomic regression. A P-value < 0.05 was considered to be significant. Between 29 May 2002 to 4 June 2002 in Salamanca, 90 patients were examined in emergency departments for pollinosis, of whom 31 sought assistance in the 24 h following the storm (Fig. 1A), which corroborates the reports of our pollinic patients. The circadian periodicity of some important allergenic pollens observed during stable sunny weather was lost during our study period. In the evening of 1 June 2000, after the dry storm, a peak of pollen levels was observed at the same time as a peak in visits to emergency departments for pollinosis (Fig. 1B), but we observed other higher peak pollen levels in the period of study not accompanied by increases in emergency visits. In fact, there was no significant correlation between the levels of any pollen and emergency visits. Climatologically, the period of study was characterized by low atmospheric pressure (Fig. 1E). Temperature and relative humidity showed the habitual circadian pattern (Fig. 1E). Only a slight decrease in temperature was observed during the last two days of the study period (the cold front of the storm). The only factor that showed a clear variation related to dry storm and increase in emergency visits for pollinosis was wind speed. Whereas in the rest of the study period, wind speed fluctuated following a circadian pattern under a value of 3.5 m/s, dry storm was characterized by a sharp increase in wind speed (to 8 m/s). Within hours of this peak wind speed, pollinic patients visited the local emergency departments (Fig. 1A). No significant correlations were found between meteorological variables and pollen levels. During the passage of one dry storm through the city we observed that the only factor clearly associated with an increase of emergency visits for pollinosis was an increase in wind speed in the previous hours. Therefore, we infer that wind affects pollinosis symptoms by a different mechanism from merely pollen transport, at least during a dry storm. Other authors have attributed epidemics of asthma during thunderstorms to rainfall, wind, lightning, and other factors (1–3); but all the storms involved were different from that observed here because of the presence of rainfalls. Taylor et al. (4) recently demonstrated that after a cycle of wetting and drying followed by wind disturbance, grasses produced an aerosol of particles; the allergenicity of these aerosols has been demonstrated by other authors (5, 6). In the days previous to the dry storm, there were no rainfalls, but we observed high relative humidity throughout the study period, which perhaps played a role in releasing micronic allergenic particles. In conclusion, it seems that dry storms – ‘perfect storms’ – establish ideal conditions to trigger pollen allergic symptoms during spring time. In these conditions, pollen level is not the only factor which determines the symptomatology of pollinic patients.