The effects of privet exposure on asthma morbidity

To determine whether privet may be an important cause of asthma morbidity.

The study was conducted in two parts; (1) a longitudinal study of asthma symptoms, medication use, peak expiratory flow rate and airway responsiveness during and after the privet-flowering season, and (2) bronchial challenge of 17 subjects with two species of flowering privet. Subjects were asthmatics who attributed worsening asthma symptoms to privet exposure. All subjects were atopic and had perennial asthma symptoms requiring treatment with inhaled steroids and beta agonists.

1. Twenty subjects completed the longitudinal study. Airway responsiveness (PD20 histamine) was significantly greater during the privet-flowering season (0.4 mumol vs 0.73 mumol, p < 0.05). Symptom scores and bronchodilator use were higher and peak expiratory flow rates lower during the privet-flowering season, but the changes were small and not statistically significant. 2. Seventeen subjects from the longitudinal study subsequently had bronchial challenge studies performed. There were no isolated early responses, but six had late asthmatic responses. Eleven had no airway constrictor response to challenge with either of the two local varieties of privet.

Although significant increases in airway responsiveness occur during the privet flowering season, only a proportion of this highly select group had a constrictor response to direct challenge. Privet exposure may cause bronchoconstriction in certain individuals, but it is unlikely to be responsible for a large proportion of asthma morbidity in New Zealand.