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Respirable aerosols (< 5 µm in diameter) present a high risk of SARS-CoV-2 transmission. Guidelines recommend using aerosol precautions during aerosol-generating procedures, and droplet (> 5 µm) precautions at other times. However, emerging evidence indicates respiratory activities may be a more important source of aerosols than clinical procedures such as tracheal intubation. We aimed to measure the size, total number and volume of all human aerosols exhaled during respiratory activities and therapies. We used a novel chamber with an optical particle counter sampling at 100 l.min -1 to count and size-fractionate close to all exhaled particles (0.5-25 µm). We compared emissions from ten healthy subjects during six respiratory activities (quiet breathing; talking; shouting; forced expiratory manoeuvres; exercise; and coughing) with three respiratory therapies (high-flow nasal oxygen and single or dual circuit non-invasive positive pressure ventilation). Activities were repeated while wearing facemasks. When compared with quiet breathing, exertional respiratory activities increased particle counts 34.6-fold during talking and 370.8-fold during coughing (p < 0.001). High-flow nasal oxygen 60 at l.min -1 increased particle counts 2.3-fold (p = 0.031) during quiet breathing. Single and dual circuit non-invasive respiratory therapy at 25/10 cm.H 2 O with quiet breathing increased counts by 2.6-fold and 7.8-fold, respectively (both p < 0.001). During exertional activities, respiratory therapies and facemasks reduced emissions compared with activities alone. Respiratory activities (including exertional breathing and coughing) which mimic respiratory patterns during illness generate substantially more aerosols than non-invasive respiratory therapies, which conversely can reduce total emissions. We argue the risk of aerosol exposure is underappreciated and warrants widespread, targeted interventions., (© 2021 Association of Anaesthetists.)

Background: Prototype nasal filters were developed to collect inhaled pollen. This study evaluated the efficacy of the filters for prevention of rhinitis symptoms during acute outdoor pollen exposure., Methods: A randomized double-blind design was used. Subjects (n=46) with a history of autumn exacerbation of rhinitis and positive skin test to ragweed, Bermuda and/or Bahia grass wore either active or placebo nasal filters for 2 h in autumn in a park containing these species. Major and Total Symptoms scores were recorded at 0, 30, 60, 90 and 120 min., Results: Subjects wearing active nasal filters had significantly reduced scores, at all time-points compared with placebo group (all P <0.05). Of 14 individual symptoms measured, seven were significantly reduced (number of sneezes, runny nose, itchy nose, sniffles, itchy throat; itchy eyes and watery eyes) and another three showed a trend towards lower severity. The nasal filters also enabled the resolution of existing symptoms. Maximal difference in symptoms was seen immediately after subjects had spent 20 min sitting beside a large patch of ragweed., Conclusion: This is the first clinical trial of a nasal filter. The results suggest it has potential for enhancing rhinitis management during acute allergen exposure.

Background: Simple, inexpensive methods of sampling from allergen reservoirs are necessary for large-scale studies or low-cost householder-operated allergen measurement., Methods: We tested two commercial devices: the Indoor Biotechnologies Mitest Dust Collector and the Drager Bio-Check Allergen Control; two devices of our own design: the Electrostatic Cloth Sampler (ECS) and the Press Tape Sampler (PTS); and a Vacuum Sampler as used in many allergen studies (our Reference Method). Devices were used to collect dust mite allergen samples from 16 domestic carpets. Results were examined for correlations between the sampling methods., Results: With mite allergen concentration expressed as microg/g, the Mitest, the ECS and the PTS correlated with the Reference Method but not with each other. When mite allergen concentration was expressed as microg/m2 the Mitest and the ECS correlated with the Reference Method but the PTS did not. In the high allergen conditions of this study, the Drager Bio-Check did not relate to any methods., Conclusions: The Mitest Dust Collector, the ECS and the PTS show performance consistent with the Reference Method. Many techniques can be used to collect dust mite allergen samples. More investigation is needed to prove any method as superior for estimating allergen exposure.

Background: Measurement of exposure to the dust mite allergen Der p 1 is important in asthma research and is potentially useful in managing asthma. As no single measure can capture all characteristics of an exposure, it is important to recognize differences in the available methods of measuring exposure to Der p 1., Methods: Fourteen bedrooms and living rooms were sampled using four methods for 1 week. Airborne allergen was sampled by static Institute of Occupational Medicine samplers. Settling dust was collected on Petri dishes and an adhesive-membrane system (A-book). Vacuumed reservoir dust samples were collected from floors at the end of 1 week. Der p 1 was measured in all samples by enzyme-linked immunosorbent assay, except A-books, in which it was measured by Halogen immunoassay., Results: All four methods intercorrelated moderately (r range = 0.40-0.64, P = 0.04), except between allergen in reservoir dust (as microg/m2 and microg/g dust) and settling dust by Petri dishes (P = 0.2). Reservoir allergen, expressed as microg/m2, did not correlate with any measure, except reservoir allergen expressed as microg/g (r = 0.39, P = 0.04). No differences in these associations occurred between bedrooms and living rooms., Conclusions: While the four methods examined correlated moderately, all have practical advantages and difficulties. No method can be considered as ideal for measuring individual exposure. For practicality, use of vacuum cleaner and Petri dish methods are recommended.

Background: In temperate climates, exposure to house dust mite (HDM) allergens is the strongest environmental risk factor for childhood asthma. Environmental modifications to limit exposure have the potential to reduce the prevalence of asthma. The aim of this study was to reduce allergen exposure for children at high risk of developing asthma., Methods: A total of 616 pregnant women were randomized to HDM intervention and control groups. The control group had no special recommendations whereas the intervention group was given allergen impermeable mattress covers and an acaricidal washing detergent for bedding. Children were visited regularly until 18 months of age to have dust collected from their bed., Results: Der p 1 concentrations in the control group increased from 5.20 microg/g at 1 month to 22.18 microg/g at 18 months but remained low in the intervention group, ranging from 3.27 microg/g at 1 month to 6.12 microg/g at 18 months., Conclusions: In a high HDM allergen environment, a combined approach using physical barriers and an acaricidal wash, is effective in reducing HDM allergen concentrations in bedding. However, even with these control measures in place, HDM allergen levels remained high by international standards.

Background: In coastal Australia, mean house-dust-mite allergen concentration is 20-40 times higher in homes than in public buildings. Allergen concentrations in university colleges, which share some characteristics of both homes and public buildings, are not known. The study aimed to compare bed mite-allergen concentration in colleges with local homes., Methods: Mattress dust was collected from three colleges (n = 60 in each) and local homes (n = 68) during summer. Der p 1 was measured by ELISA. Information was collected on the floor plan of the colleges, cleaning practices, age of building, and orientation of room., Results: Most college mattresses (94%) had Der p 1 concentrations less than the mean of homes in the same climate. The geometric means of Der p 1 in the mattresses of the colleges were as follows: A, 8.9 micrograms Der p 1/g fine dust (95% CI 6.9, 11.5); B, 1.9 (1.5, 2.3); and C, 1.5 (1.2, 2.0), compared to homes, 22.5 (17.6, 28.7). The percentages of college mattresses with less than 2 micrograms/g were 7%, 48%, and 58%, respectively, compared to 4% for homes. Higher Der p 1 concentrations were weakly associated with age of building in college A, and orientation in college B. Der p 1 concentrations were independent of floor level and age of mattress., Conclusions: These findings indicate that low allergen concentrations are achievable without extreme hygiene and cleaning measures in a climate which supports mite proliferation in homes.