Simon C.O. Taggart

Exposure to house dust mite allergens and the clinical activity of asthma

BACKGROUND House dust mite allergens play an important role in inducing IgE-mediated sensitization and the development of bronchial hyperresponsiveness (BHR) and asthma. This study investigated the relationship between mite allergen exposure and the clinical activity and severity of asthma. METHODS Nonsmoking adult patients with asthma (n = 53) were randomly recruited from the asthma registry of two large family practitioner surgeries. Each participant underwent skin testing with common inhalant allergens, a methacholine bronchoprovocation test, and pulmonary function testing on up to 3 separate occasions over a 4-week period. BHR was expressed both as PD20 and dose-response ratio (DRR), and the patients with patients with PD20 of less than 12.25 mumol methacholine were classified as methacholine reactors. Patients were also asked to record peak expiratory flow rate (PEFR) values at 2-hour intervals during waking hours for 1 month. Daily PEFR variability was calculated as amplitude percent mean. Dust samples were collected by vacuuming bedding, bedroom carpets and mattresses. In addition, in the homes of 32 subjects with positive skin test responses to mites, airborne samples were taken overnight for 8 hours with a personal sampler attached to each subjects pillow. Der p 1 and Der p 2 levels were determined by a two-site monoclonal antibody-based ELISA. RESULTS No difference in mite exposure was found between subjects who were sensitive to mites and those who were not. However, mite-sensitive methacholine reactors were exposed to significantly higher concentrations of Der p 1 in beds than mite-sensitive methacholine nonreactors (13.2 micrograms/gm and 1.45 micrograms/gm, respectively; p < 0.02). Der p 1 and Der p 2 were undetectable in 30 of 32 airborne samples. In mite-sensitive patients both Der p 1 and Der p 2 in beds significantly correlated with BHR (PD20: r = -0.49, DRR, r = 0.49; PD20: r = -0.46, DRR: r = 0.43) and amplitude percent mean PEFR (r = 0.38, r = 0.41) for Der p 1 and Der p 2, respectively. There was a significant negative correlation between exposure to Der p 1 and percent predicted FEV1 (r = -0.43). The correlation between Der p 2 and percent predicted FEV1 just failed to reach a significant level but showed a clear trend ( r = -0.35, p = 0.068). CONCLUSIONS Clinical activity and severity of asthma (measured by the level of BHR, PEFR variability, and percent predicted FEV1) in mite-sensitive patients is related to exposure to mite allergens in the dust reservoir, with levels in bed being an important indicator that correlated with disease activity.

Domestic allergens in public places II: dog (Can f 1) and cockroach (Bla g 2) allergens in dust and mite, cat, dog and cockroach allergens in the air in public buildings

Background Sensitization and exposure to indoor allergens are the major risk factors for asthma. It is possible that significant exposure to domestic allergens occurs outside the home.

House dust mite and cat allergen in different indoor environments

Allergy to house dust mites (HDM) and domestic pets is a major cause of asthma. People in developed countries spend more than 90% of their time indoors. We have measured levels of HDM allergen Der p I and cat allergen Fel d I in public buildings and public transport. Dust samples were collected by vacuuming a 1 m2 area for 2 min from five schools, six hotels, four cinemas, six pubs, three buses, two trains and 12 domestic households without a cat. Der p I and Fel d I were assayed with monoclonal antibodies in a two‐site immunometric ELISA. Der p I concentration was significantly higher in the private homes than in comparable sites in public places except for cinema seats (where high values were found) compared with domestic sofas. Der p I >2000 ng/g of fine dust was found in 30% of the upholstered seats, 9% having a concentration > 10000 ng/g. Fel d I levels were significantly higher in the dust from upholstered seats (geometric mean 14±88 μg/g) than in carpeted floors (geometric mean 0±73 μg/g), and in public places than in private homes. Fel d I >8 μg/g was found in 79% of the upholstered seats or furniture sampled in public buildings or public transport. In conclusion, upholstered seats from public buildings and public transport constitute an allergen reservoir for continuous contamination of the indoor environment which could compromise the effects of allergen avoidance employed at home.

Portable dehumidifiers in the control of house dust mites and mite allergens.

Humidity is a decisive limiting factor for house dust mite (HDM) population growth and decreasing humidity may be the control method of choice. This study investigates the effects of portable dehumidifiers on the mite counts and concentration of the HDM allergen Der p I in the homes in northwest England. Mite counts and Der p I were measured in the paired dust samples collected by vacuuming a I m2 area of bedroom carpet, living room carpet, mattress and sofa for 2 min in six houses supplied with the dehumidifier and six control houses, before and 1, 2 and 3 months after the instalment of dehumidifier. Temperature and relative humidity were recorded daily. There was no difference in mite counts in either of the groups throughout the study. Der p I decreased significantly in both groups and in all sampling sites, but no significant differences in the levels of reduction between the groups were found. Condensation was decreased in the dehumidifier group, but the level of indoor humidity capable of retarding mite population growth was not achieved. A single portable dehumidifier placed centrally in the house is unable to decrease indoor humidity to the level capable of retarding mite population growth and decreasing HDM allergens in the type of houses predominantly found in the northwest of England.

Evaluating exposure to mite allergens

Standardized methods for measuring mite allergen exposure are essential for assessing the relationship between exposure and sensitization and the degree of exposure associated with provocation of asthma symptoms. However, there is still considerable debate as to whether exposure should be assessed by measuring settled dust from allergen reservoirs or by sampling ambient air and whether results for settled dust should be expressed as recoverable allergen per unit weight or per unit area. 1-5 The aim of this study was to compare methods for collecting and analyzing allergen samples.

GR106642X: a new, non-ozone depleting propellant for inhalers

Metered dose inhalers are the most popular choice of drug delivery system for treating asthma and chronic airflow limitation. Unfortunately, they contain chlorofluorocarbon propellants, which contribute to the depletion of stratospheric ozone.1 The Montreal Protocol of 1987 has therefore called for a gradual phasing out of manufacture of chlorofluorocarbons in all developed countries by 1996. Inhalers containing chlorofluorocarbons have been given a temporary exemption, but there remains considerable environmental pressure for their early withdrawal. GR106642X (1, 1, 1, 2-tetrafluoroethane) is a new propellant which does not deplete ozone. It has been used alone, with no other excipients, to reformulate salbutamol. We investigated the safety and efficacy of the new non-ozone depleting formulation for salbutamol in a randomised, double blind, placebo controlled, crossover comparison with the traditional salbutamol inhaler containing chlorofluorocarbons 11 and 12 (Ventolin, Allen …

Asthmatic bronchial hyperresponsiveness varies with ambient levels of summertime air pollution

It is widely believed that the mechanisms of action of outdoor air pollutants are the same as those found in the laboratory, although few studies have attempted to clarify this issue. This study investigates the relationship of asthmatic bronchial hyperresponsiveness (BHR), a marker of airway inflammation, and pulmonary function to ambient levels of summertime air pollution. Thirty eight nonsmoking adult asthmatic subjects underwent repeated measurement of methacholine BHR, using Yans method, at differing levels of air pollution (O3, SO2, NO2, smoke) during summer 1993. A total of 109 evaluable tests were performed: 31 subjects completed three or more challenge tests, and seven managed two. Levels of all pollutants remained within current World Health Organization (WHO) Guidelines for Health. Changes in BHR were found to correlate significantly with changes in the levels of 24 h mean SO2, NO2 and smoke; 48 h mean NO2 and smoke; 24 h lag NO2; although the effect was only small, accounting for approximately 10% of the variability in within-subject BHR between visits. Twenty four hour lag NO2 was also associated with forced vital capacity (FVC). In conclusion, in subjects with asthma, methacholine bronchial hyperresponsiveness varies with ambient levels of summertime air pollution. This suggests that changes in airway inflammation underlie the increased respiratory morbidity known to accompany pollution episodes.

Seasonal variability in exercise test responses in Ghana

Exercise‐induced bronchospasm (EIB) is widely used in epidemiological studies to investigate the prevalence of asthma. We aimed to determine seasonal variations in the prevalence of EIB in Ghanaian school children from urban‐rich (UR), urban‐poor (UP), and rural (R) schools. We have previously reported the prevalence of EIB in 9–16‐year‐old children to be 3.1% in the dry season, with UR children having a significantly higher prevalence of both EIB and atopy compared to UP or R children. In the current study, the prevalence of EIB was assessed in the same 1,095 children in the wet season (5 months following the initial study) using the same methodology. Exercise provocation consisted of free running outdoors for 6 min. In the wet season, 17/1,095 children [mean 1.55%, 95% confidence interval (CI): 0.91–2.47] had a positive response to exercise, compared to our previous report of 34 children (mean 3.1%, 95% CI: 2.15–4.32) with EIB in the dry season (dry vs. wet season, difference 1.55, 95% CI: 0.41–2.69). The proportion of children with a positive response to exercise in the UR school fell from 4.2% (25/599) to 1.3% (8/599) (difference 2.9, 95% CI: 1.2–4.5). In the wet season, there was no difference in the prevalence of EIB among the UR, UP, and R children. Only five of 1,095 subjects (mean 0.5%, 95% CI: 0.15–1.07) demonstrated EIB in both seasons. In conclusion, although exercise challenge remains a useful tool for determining asthma prevalence in epidemiological studies, seasonal variations in the pattern of responses may occur and the results should be interpreted with caution.