If house dust mite allergen (Der p I) is an important cause of asthma, there should be a direct relationship between level of exposure to this allergen and asthma severity. To examine this, we studied six large random samples of children in different regions of New South Wales, Australia. We measured recent wheeze by questionnaire, airway hyperresponsiveness (AHR) by histamine inhalation test and sensitization to house dust mites by skin prick tests. Current asthma was defined as the presence of recent wheeze and AHR. We measured Der p I levels in the beds of approximately 80 children in each region. In regions where Der p I levels were high, more children were sensitized to house dust mites, and these children had significantly more AHR and recent wheeze. After adjusting for sensitization to other allergens, we found that the risk of house dust mite-sensitized children having current asthma doubled with every doubling of Der p I level. There was a modest correlation between AHR and Der p I exposure in individuals (r = 0.23, p < 0.03). These data suggest that house dust mite allergens are an important cause of childhood asthma and that reducing exposure to these allergens could have a large public health benefit in terms of asthma prevention.

Guidelines and governments must acknowledge the evidence and take steps to protect the public

Aerosol transmission routes of respiratory viruses have been classified by the WHO on the basis of equilibrium particle size. Droplet transmission is associated with particles sized >5 µm in diameter and airborne transmission is associated with particles sized ≤5 µm in diameter. Current infection control measures for respiratory viruses are directed at preventing droplet transmission, although epidemiological evidence suggests concurrent airborne transmission also occurs. Understanding the size of particles carrying viruses can be used to inform infection control procedures and therefore reduce virus transmission. This study determined the size of particles carrying respiratory viral RNA produced on coughing and breathing by 12 adults and 41 children with symptomatic respiratory infections. A modified six-stage Andersen Sampler collected expelled particles. Each stage was washed to recover samples for viral RNA extraction. Influenza A and B, parainfluenza 1, 2 and 3, respiratory syncytial virus (RSV), human metapneumovirus and human rhinoviruses (hRV) were detected using RT-PCR. On breathing, 58% of participants produced large particles (>5 µm) containing viral RNA and 80% produced small particles (≤5 µm) carrying viral RNA. On coughing, 57% of participants produced large particles containing viral RNA and 82% produced small particles containing viral RNA. Forty five percent of participants produced samples positive for hRV viral RNA and 26% of participants produced samples positive for viral RNA from parainfluenza viruses. This study demonstrates that individuals with symptomatic respiratory viral infections produce both large and small particles carrying viral RNA on coughing and breathing.