Is quantitative PCR for the pneumolysin (ply) gene useful for detection of pneumococcal lower respiratory tract infection?

The pneumolysin (ply) gene is widely used as a target in PCR assays for Streptococcus pneumoniae in respiratory secretions. However, false-positive results with conventional ply-based PCR have been reported. The aim here was to study the performance of a quantitative ply-based PCR for the identification of pneumococcal lower respiratory tract infection (LRTI). In a prospective study, fibreoptic bronchoscopy was performed in 156 hospitalized adult patients with LRTI and 31 controls who underwent bronchoscopy because of suspicion of malignancy. Among the LRTI patients and controls, the quantitative ply-based PCR applied to bronchoalveolar lavage (BAL) fluid was positive at >or=10(3) genome copies/mL in 61% and 71% of the subjects, at >or=10(5) genome copies/mL in 40% and 58% of the subjects, and at >or=10(7) genome copies/mL in 15% and 3.2% of the subjects, respectively. Using BAL fluid culture, blood culture, and/or a urinary antigen test, S. pneumoniae was identified in 19 LRTI patients. As compared with these diagnostic methods used in combination, quantitative ply-based PCR showed sensitivities and specificities of 89% and 43% at a cut-off of 10(3) genome copies/mL, of 84% and 66% at a cut-off of 10(5) genome copies/mL, and of 53% and 90% at a cut-off of 10(7) genome copies/mL, respectively. In conclusion, a high cut-off with the quantitative ply-based PCR was required to reach acceptable specificity. However, as a high cut-off resulted in low sensitivity, quantitative ply-based PCR does not appear to be clinically useful. Quantitative PCR methods for S. pneumoniae using alternative gene targets should be evaluated.

Potential side effects in patients treated with inhaled corticosteroids and long-acting beta2-agonists.

BACKGROUND: Long-acting-beta-agonists and inhaled corticosteroids are widely used in patients with obstructive lung disease. We determined the occurrence of potential side effects to inhaled steroids and long-acting-beta-agonists in an open post-marketing observational study. METHODS: A total of 158 adult patients treated with long-acting-beta-agonists and inhaled steroids because of asthma or chronic obstructive lung disease were included prospectively in a cross-sectional study from September 2004 through august 2005. A subgroup of 31 patients with minimal disease were observed prospectively after treatment reduction. The frequency and intensity of potential side effects to long-acting-beta-agonists and inhaled corticosteroids were registered on a 10-point visual analogue scale. RESULTS: A total of 131 (83%) reported potential side effects to inhaled steroids. The most frequent were sore (54%) and dry (52%) throat. A total of 114 (72%) patients reported potential side effects to long-acting-beta-agonists. The most frequent were muscle cramps (62%) and muscle twisting (39%). For 5/8 potential side effects their occurrence increased with increased individual dozing. In 31 patients the mean medication with steroids and long-acting-beta-agonists was reduced by 87% and 97.5%, respectively, with side effects reduced by 62% (p<0.001) to inhaled steroids and by 91% (p<0.001) to inhaled long-acting-beta-agonists. CONCLUSIONS: Potential side effects in adult patients to inhaled corticosteroids and long-acting-beta-agonists are very common with increased frequency with increased dozing. Patients are largely unaware of the association. Patients should be better informed, and the results further support tailored dozing to minimum therapy.

Bacterial colonisation of lower airways in health and chronic lung disease.

BACKGROUND: To evaluate the colonisation rate and type in different groups of patients with chronic lung diseases, bronchial lavage (BL) fluid was investigated for bacteria. METHODS: All patients underwent fibre-optic bronchoscopy as part of routine investigation for remote haemoptysis or nodule investigation. The standard procedure included BL and microbiological culture providing the total number of colony forming units (cfu)/mL and the number of potential pathogenic bacteria (ppb)/mL. Three groups of patients were included: 48 persons had a final diagnosis of no pathology, 53 patients with chronic obstructive pulmonary disease in a stable phase and 32 patients with a final diagnosis of bronchiectasis. RESULTS: The median number of cfu cultured from patients with bronchiectasis was 10(5) cfu/mL compared to 5 10(3) cfu/mL in patients with COPD and 10(4) cfu/mL in persons with no pathology. The ppb colonisation rate varied from 10% in persons with no pathology to 43% in patients diagnosed with chronic obstructive pulmonary disease (COPD) and 63% in patients with bronchiectasis. The most frequent bacteria isolated was Haemophilus influenzae. Colonisation rates were associated with frequencies of respiratory infections; patients with bronchiectasis reported a median of three infections per year, patients with COPD reported one infection per year, and persons without pathology reported 0 infections per year (P < 0.05). Within each group a large patient-to-patient variation was found. CONCLUSIONS: Different groups of patients with chronic pulmonary diseases have very different colonisation rates. Patients with bronchiectasis have the highest colonisation rate. This correlates to the reported frequency of lower respiratory tract infections.

Evaluation of a multiplex PCR for bacterial pathogens applied to bronchoalveolar lavage.

The present study assessed the diagnostic usefulness of a multiplex PCR (mPCR) for Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae and Chlamydophila pneumoniae applied to bronchoalveolar lavage (BAL). Fibreoptic bronchoscopy was performed on 156 hospitalised adult patients with lower respiratory tract infection (LRTI) and 36 controls. BAL fluid was analysed with bacterial culture and mPCR. By conventional diagnostic methods, S. pneumoniae, H. influenzae, M. pneumoniae and C. pneumoniae were aetiological agents in 14, 21, 3.2 and 0% of the LRTI patients, respectively. These pathogens were identified by BAL mPCR in 28, 47, 3.2 and 0.6% of cases, respectively, yielding sensitivities of 86% for S. pneumoniae, 88% for H. influenzae, 100% for M. pneumoniae and 0% for C. pneumoniae, and specificities of 81, 64, 100 and 99% for S. pneumoniae, H. influenzae, M. pneumoniae and C. pneumoniae, respectively. Of the 103 patients who had taken antibiotics prior to bronchoscopy, S. pneumoniae was identified by culture in 2.9% and by mPCR in 31%. Among the controls, mPCR identified S. pneumoniae in 11% and H. influenzae in 39%. In lower respiratory tract infection patients, bronchoalveolar lavage multiplex PCR can be useful for identification of Streptococcus pneumoniae, Mycoplasma pneumoniae and Chlamydophila pneumoniae. The method appears to be particularly useful in patients treated with antibiotics.

House-dust mites and summer cottages.

BACKGROUND: Estimated indoor climate conditions in unheated summer cottages offers house-dust mites unfavorable temperature and feeding conditions while giving them optimum humidity conditions. We aimed to estimate the exposure level of house-dust mites in summer cottages. METHODS: A total of 37 summer cottages were sampled for house dust and storage mites in three locations and the results compared with samples from 33 patients suspected of house-dust mite allergy and living in ordinary houses. The processed dust samples were investigated by microscopy and exposure levels given as number of mites per 0.1 g dust. RESULTS: The summer cottages were without exception all heavily infested with threefold or higher concentrations of both house dust and storage mites in comparison with ordinary houses. In unheated summer cottages were found tropical high concentrations of house dust and storage mites with a median concentration of house-dust mites in mattress dust of 2000 house-dust mites/g of dust which corresponds to an average of 40 microg allergen/g of mattress dust. CONCLUSIONS: As a probable consequence of high indoor air humidity conditions in unheated summer cottages in winter, dust samples contained threefold or higher concentrations of house dust and storage mites. Indoor humidity conditions thus more than compensated for lack of continuous supply of skin scales from human beings and an unfavorable low indoor air temperature. The uniform high mite exposure in summer cottages is likely to imply disease deterioration in patients already allergic to mites.

Indoor exposures and recurrent wheezing in infants: a study in the BAMSE cohort.

AIM: The aim of this study was to examine the relationship between indoor exposures and the home environment, and the development of recurrent wheezing during infancy. METHODS: A birth cohort, comprising 4089 children, was followed. Information on exposures was obtained shortly after birth, and episodes of wheezing were recorded when the infants were 1 and 2 y of age. In a nested case-control study, 181 infants were enrolled, who had three or more reported episodes of wheezing after 3 mo of age combined with either use of inhaled steroids or symptoms of bronchial hyper-reactivity, and 359 age-matched controls. Home inspections were performed during the winter following enrolment, and indoor conditions were measured. RESULTS: Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated. The OR for recurrent infant wheezing associated with signs of dampness reported prospectively by parents was 1.4 (0.9-2.2), and the OR for observed signs of dampness at home inspections was 1.6 (1.0-2.5). A trend was found in the risk of recurrent wheezing in relation to the number of indicators of dampness: OR 1.3 (0.8-2.2) for one sign of dampness and OR 2.7 (1.3-5.4) for three or more signs of dampness. Newly painted surfaces in the child's bedroom was associated with an increased OR for recurrent wheezing: 1.7 (1.3-2.6). CONCLUSION: Indicators of dampness, as well as recently repainted interior surfaces, appear to be associated with recurrent infant wheezing, with a strengthened effect of combined indoor exposures.

Building characteristics, indoor air quality and recurrent wheezing in very young children (BAMSE).

This study was conducted to examine the impact of building characteristics and indoor air quality on recurrent wheezing in infants. We followed a birth cohort (BAMSE) comprising 4089 children, born in predefined areas of Stockholm, during their first 2 years of life. Information on exposures was obtained from parental questionnaires when the children were 2 months and on symptoms and diseases when the children were 1 and 2 years old. Children with recurrent wheezing, and two age-matched controls per case, were identified and enrolled in a nested case-control study. The homes were investigated and ventilation rate, humidity, temperature and NO2 measured. We found that living in an apartment erected after 1939, or in a private home with crawl space/concrete slab foundation were associated with an increased risk of recurrent wheezing, odds ratio (OR) 2.5 (1.3-4.8) and 2.5 (1.1-5.4), respectively. The same was true for living in homes with absolute indoor humidity >5.8 g/kg, OR 1.7 (1.0-2.9) and in homes where windowpane condensation was consistently reported over several years, OR 2.2 (1.1-4.5). However, air change rate and type of ventilation system did not seem to affect the risk. In conclusion, relatively new apartment buildings, single-family homes with crawl space/concrete slab foundation, elevated indoor humidity, and reported wintertime windowpane condensation were associated with recurrent wheezing in infants. Thus, improvements of the building quality may have potential to prevent infant wheezing.

Allergen sensitization and allergen exposure in Greenlander Inuit residing in Denmark and Greenland.

The aim of this study was to estimate the prevalence of allergic sensitization and possible risk factors in a genetically homogenous Inuit population living under widely differing climatic and cultural conditions. A written questionnaire and skin prick test for 10 aeroallergens were obtained from 1119 adult Greenlanders residing in Denmark, Nuuk (main city in Southern Greenland) and Uummannaq (rural settlement in Northern Greenland). Allergen exposure was assessed by pollen counts, questions on pet keeping and counts of house dust mites in dust samples. The overall prevalence of at least one positive skin prick test was 22.8% in Denmark, 10.6% in Nuuk, and 6.4% in Uummannaq. In Denmark, the total birch pollen counts were 40-1000 times higher compared to Nuuk, whereas the grass pollen count was 13-30 times higher in Denmark compared to Nuuk. Dogs were held indoor with a similar frequency in Denmark and Nuuk, but much less frequently in Uummannaq. In Denmark, house dust mites were found in 72% of house holds (>10/0.1 g dust). Less than 15% of households in Greenland had measurable levels of house dust mites. The prevalence of sensitization to aeroallergens in Inuit Greenlanders differed significantly between Denmark, Nuuk and Uummannaq. These findings correlated with the observed differences in population allergen exposure in the three regions. Furthermore, differences in lifestyle factors such as educational level, stress and ethnic self-identification seemed to be associated with the risk of allergic sensitization in Greenland.

Intensified microbiological investigations in adult patients admitted to hospital with lower respiratory tract infections.

The objective of this study was to investigate the diagnostic yield of a programme with intensified microbiological investigations in immunocompetent adult patients with lower respiratory tract infections (LRTI). Patients in the study group were included prospectively and consecutively from September 1st 1997 to May 31st 1998 and were compared with a control group from the preceding year. A total of 67 adult patients were included in the study group and they were compared with 122 adult patients in the control group. The study group underwent fibre-optic bronchoscopy (FOB) with bronchoalveolar lavage (BAL). Only 7% in the historic control group were discharged with an aetiological diagnosis of their infections; while the diagnostic yield in the study group increased to 51% of patients. In the study group the presence of new infiltrates on chest X-ray increased the detection of a microbiological aetiology from 37% with no infiltrates to 62% with infiltrates and recent antibiotic therapy reduced the detection of a microbiological cause of infection from 61% in 36 patients who had not received antibiotic therapy to 39% in 31 patients who had received recent antibiotic therapy prior to microbiological sampling. Patients in the study group with known aetiology had higher values of inflammatory markers than patients with unknown aetiology. For Streptococcus pneumoniae infection culture and urine antigen detection were complimentary depending on recent antibiotic therapy since seven of eight culture-positive patients had not received antibiotic therapy within 72 h prior to investigation, while all four patients positive for urine antigens from S. pneumoniae had received antibiotic therapy within 72 h of urine sampling. In conclusion intensified microbiologic investigations increase the diagnostic yield from 7% to 51% of patients in the study group with an aetiologic diagnosis. Routine FOB with BAL had no apparent effect on clinical outcome and seems only justified in selected patients with severe LRTI with infiltrates on chest X-ray and signs of severe inflammation where a high diagnostic yield is achieved.

Quantitative culture of bronchoalveolar lavage fluid in community-acquired lower respiratory tract infections.

To evaluate the diagnostic value of quantitative bacterial culture of bronchoalveolar lavage (BAL) fluid obtained by fibreoptic bronchoscopy, 67 consecutive immunocompetent adult patients admitted to hospital with community-acquired lower respiratory tract infections from September 1997 to May 1998 were investigated. Results were compared to the findings in eight healthy control persons investigated in February 1998. There was no difference between study patients and control persons when quantitative culture of total cumulative bacterial findings or bacteria categorized as members of the oropharyngeal normal flora were compared. The culture of normal flora in bronchial washings probably reflects contamination of the lower airways with secretions from upper arways by the fibreoptic procedure itself, as fractionated sampling showed a 10-fold reduct on in quantitative culture results when a primary bronchial washing was compared to a secondary sampling from the same bronchus in the control group. Twenty-four (36%) of 67 patients were cultured as positive in the study group while all control persons were cultured as negative for bacteria categorized as potential pathogens. With a threshold value for positive culture of 10(4) cfu ml(-1) the specificity of lavage culture of potential pathogenic bacteria in relation to actual lower airway infection was 100%. Therefore, quantitative bacterial culture of potential pathogenic bacteria in BAL fluid is very specific but only positive in about one-third of unselected immunocompetent adult patients with a lower respiratory tract infection.

Window pane condensation and high indoor vapour contribution - markers of an unhealthy indoor climate?

OBJECTIVE: The aim of this study was to investigate whether window pane condensation and indoor vapour contribution >/= 3 g/m3 could be used as indicators of defective air change rate, high indoor humidity and high mite allergen concentration in mattress dust. METHODS: Actual ventilation rate, indoor temperature, air humidity (AIH/RH) and concentrations of mite allergen were measured in 59 houses and compared with received outdoor temperatures and air humidity. Indoor vapour contribution defined as the difference between the indoor and the outdoor vapour concentration was calculated. Sensitivity, specificity, predictive values and accuracy were calculated for window pane condensation and high vapour contribution (>/= 3 g/m3), as indicators of defective ventilation (< 0.5 ACH), high indoor humidity (>/= 7 g/kg and >/= 45% RH) and high mite allergen concentration in mattress dust (>/= 2 microg/g). RESULTS: All houses with high humidity and high mite allergen concentrations were positive for the two indicators (high sensitivity), but with a specificity of only 50% so that half of the houses with reported condensation and high vapour contribution turned out to be low pollution houses with adequate high ventilation levels. Both indicators had high negative predictive values and absence of the two indicators almost certainly (97-100%) excluded high indoor pollution with high humidity and high mite concentrations. Overall more than 70% of the dwellings were correctly classified by the two indicators. CONCLUSION: Absence of window pane condensation on double-glazed windows and low indoor vapour contribution (< 3 g/m3) during the winter are true markers of a dwelling without high indoor air humidity and without high mite allergen concentrations in mattress dust in houses in a cold temperate climate with subzero outdoor temperatures. The presence of the two indicators is associated with a 18-45% risk of high humidity and mite allergen concentrations so in this latter group further measurements are needed for correct classification.

Epidemiology of house-dust mites.

Available epidemiologic data on the occurrence of house-dust mites in dwellings demonstrates a clear association between increased indoor air humidity and the increased occurrence of house-dust mites in house dust. Furthermore, in temperate climates, there is a threshold level of indoor air humidity of 7 g/kg (45% relative humidity at usual indoor air temperatures). Indoor air humidities below this level for extended periods will eradicate house-dust mites from dwellings. A reduction in inhabitant exposure to house-dust mites is implemented by reduction of indoor air humidity by controlled mechanical ventilation. Individual ventilation levels are estimated from the actual size of house, number of inhabitants, and average outdoor air humidity in winter. In contrast, more humid areas of the world with average outdoor humidities above 6-7 g/kg in winter will support uniformly large populations of house-dust mites, and reductions in indoor air humidity will have a comparatively minor effect on the occurrence of house-dust mites. Present-day building of energy-efficient houses with increased sealing of the building envelope, paralleled by a similar renovation of older houses, has increased indoor air humidity and is probably the cause of the almost fourfold increase in the occurrence of house-dust mites in Danish dwellings.

House-dust mites and asthma. A review on house-dust mites as a domestic risk factor for mite asthma.

Increased exposure to house-dust mites entails a greatly increased frequency of sensitization and increased frequency of mite asthma in the population. The available case-control studies demonstrate large variations worldwide in sensitization and disease risk dependent on the actual level of population exposure. In areas with comparatively low population exposure to house-dust mites, there is a strong association between exposure and effect, while other areas with a more or less uniformly high population exposure do not demonstrate significant differences between patients and controls because the unexposed groups are too small. As to the existence of a hygienic maximum threshold exposure level, current data all point to a single value of 100 mites/g of dust, corresponding to 2 microg allergen/g of dust. This applies to the risk of sensitization and risk of disease, and when programs of prevention imply exposure below this value, convincing clinical improvement is always observed. Today, the magnitude of the health problem related to population exposure to house-dust mites in many areas is comparable to the effects of active tobacco smoking and traffic accidents.

Peak expiration flow variations may reflect house-dust-mite exposure and patient reactivity.

Peak expiration flow records from patients allergic to house-dust mites (Dermatophagoides spp.) may show a characteristic variation from week to week due to the general life cycle of these mites in dwellings. This was demonstrated from the combined records of 10 patients recorded in their own homes, covering a period of 30 consecutive weeks and comprising 973 peak flows. The levels of house-dust mites were predicted from published data for floor-dust samples from Danish dwellings. Peak flow increased or decreased in accordance with weekly changes in the concentration of mites, rather than as an immediate reaction to the current concentration of live, active mites. A dose-response relation was demonstrated. This suggests that the patients' peak flow variations might be linked to molting in mites. As such, peak flow measurements have a potential as a tool for the specific diagnosis of, monitoring of, and research in asthma caused by domestic mites.

Transient sensitization to house-dust mites: a study on the influence of mite exposure and sex.

This study aimed to evaluate the prognosis of a previous positive skin test to house-dust mites (HDM) in relation to environmental exposure. A total of 115 children, 50 from Stockholm and 65 from northern Sweden, all with a previous (average 2.5 years) positive Phazet (Pharmacia AB, Uppsala, Sweden) skin prick test (SPT) to extracts of Dermatophagoides pteronyssinus (Dpt) and/or D. farinae (Df) were included. Dust samples were collected from the children's mattresses, and the total (Dpt, Df, and D. microceras [Dm]) amount of major mite allergen was measured by ELISA (50 children) and expressed as microgram allergen per gram of dust, or was measured by microscopy (65 children). The results of microscopic mite counts were transformed to approximate allergen levels as 2 micrograms equals 100 mites per gram of dust. Of 115 originally SPT-positive children, only 48 (48%) remained positive at retest, while the majority (58%) were SPT negative after 2 years. Among the 67 converted children, 11 were still exposed to mite allergen, but only to low concentrations (only one converted child being exposed above the suggested threshold level [TLV] of 2 micrograms/g), compared to 15/48 children still SPT positive who were exposed above the TLV. This shows that continued mite exposure is a major risk factor (OR = 30, CI 4.8-184) for continued positive SPT to HDM. A minor risk factor for continued sensitization was sex, boys having a higher risk than girls (OR = 2.2, CI 1.0-4.8). In conclusion, a surprisingly high rate of SPT conversion occurred, mainly as a result of a favorable indoor environment with low exposure to HDM and, to a lesser degree, as a result of sex. The present results support the view that the risk level of exposure is 2 micrograms mite allergen per gram of dust.

House-dust mite content in mattresses in relation to residential characteristics and symptoms in atopic and nonatopic children living in northern Norway.

The occurrence of house-dust mites (HDMs) was investigated in the mattresses of 19 children previously found to be skin prick test (SPT) positive to HDM and in 19 nonatopic children derived from an extensive survey of 424 schoolchildren, all living in northern Norway. Domestic mites were counted and identified microscopically. Mite counts ranging from 10 to 1800 mites per gram mattress dust were found in 10 of the 19 HDM-sensitized children compared to none in the control group, corresponding to an odds ratio of more than 20. Of the 540 domestic mites found, 70 were identified by species. Dermatophagoides pteronyssinus (Dpt) was the only HDM species identified (64 mites), while five were storage mites and one was a Tarsonemus species. Positive radioallergosorbent tests (RAST) to Dpt were demonstrated in 9/10 children with and in 5/9 without mite infestation compared to none in the control group. Elevated IgE levels were also found more frequently in children with mite-infested mattresses than in those without. IgE levels were within normal levels in all 19 children in the control group. Latent atopy was found in four children, three with and one without mite infestation. There was no correlation between the concentration of mites and the degree of sensitization. Poor ventilation, increased humidity, and water leak(s) were associated with the presence of domestic mites in mattresses. As HDM growth is highly dependent on humidity and microhabitat, it should be possible to avoid HDM exposure and allergy in this region.

Clinical efficacy of reduction in house-dust mite exposure in specially designed, mechanically ventilated "healthy" homes.

In temperate climates, energy-conserving measures may increase indoor humidity, enhancing house-dust mite (HDM) growth. Movement of families to "healthy" homes with mechanical ventilation systems reduced HDM exposure. The effect on asthma control of moving to the "healthy" homes was studied in 14 asthmatic patients allergic to HDM. Base-line evaluations of lung function, asthma symptoms, and medication requirements were made before moving and again after 5 and 15 months' residence. A control group of 11 mite-sensitive asthmatic patients who did not move were examined contemporaneously with the study group at base line and at the first follow-up investigation. After 5 months, the residents of the "healthy" homes improved in forced expiratory volume in 1 s (FEV1), medicine score, and serum IgE. These changes were significantly different from control group measurements. After 15 months, statistically significant improvements from base line were found in FEV1, average daily peak expiratory flow values, medicine score, symptom score, and serum IgE. Insignificant trends toward improvement were seen in provocation concentration of histamine and blood eosinophils. A significant relation was found between reduction in medicine score and fall in HDM exposure. The present study shows that a specific HDM-avoidance procedure can result in an overall, clinical improvement in HDM-sensitive asthmatic patients.

House-dust mite exposure reduction in specially designed, mechanically ventilated "healthy" homes.

Exposure to house-dust mites (Dermatophagoides spp.) was investigated in 30 asthmatic patients before and after moving to homes with mechanical ventilation systems. Median house-dust mite concentration was 110 mites per gram of mattress dust at the initial investigation and 20 mites per gram at the first follow-up after a mean of 4.7 months in the new homes. This was lower (P < 0.05) than counts in a control group of 23 asthmatic patients that had unchanged counts. At a second follow-up, after 15.0 months, mite counts in the study group were further reduced (P < 0.01) from initial values. Among 16 patients, with initial mite counts above the recommended threshold limit value (TLV) of 100 mites per gram of dust, the mite counts fell, in most cases, below this TLV. Air-exchange rates increased (P < 0.001) from a median value of 0.40 air changes per hour (ach) to 1.52 ach at the second follow-up investigation. Furthermore, a reduction (P < 0.01) was found in indoor absolute air humidity, with a median value of 5.6 g of water/kg. No such changes were found in the control group. The present study indicates that reduction of air humidity through an increased supply of fresh air may significantly diminish and, in some cases, even eliminate house-dust mites in homes.

Mite allergens during 18 months of intervention.

In Stockholm, Sweden, 17 children with newly diagnosed sensitization to house-dust mites (HDM) and 11 children with previously diagnosed HDM-sensitization were included in a study of HDM-allergen avoidance. Mattress dust was collected on repeated occasions during 18 months and assayed for concentration of major HDM allergens. During the first 12 months, the parents of the intervention group were instructed to intensify cleaning and airing of the child's bedroom. During the last 6 months of the study, the mattresses and pillows of seven children in the intervention group and sibling controls were encased in semipermeable polyurethane covers. The homes exhibited a high absolute indoor humidity throughout the year, and even during the winter the mean levels exceeded 7 g/kg. No mite allergen reduction was seen in the intervention group during the first year. However, among the newly diagnosed HDM-sensitized children, there was a mean reduction of the mattress mite allergen concentration of 83% (P = 0.02), and this was most pronounced in the homes with low humidity. At the end of the mattress encasement period, an average difference of 98% (P < 0.001) was found between the vacuumed amount of mite allergen on top of the covers and that underneath.

Sensitization to domestic mites in a cold temperate region.

Factors favoring sensitization to house dust mites (HDM) were studied in a cold, temperate climate in northern Sweden. Sixty-five children previously found to react positively to a skin prick test (SPT) to HDM were included. The SPT to HDM was repeated, and serum IgE antibodies to D. pteronyssinus and D. farinae were determined. HDM, Euroglyphus maynei, Tarsonemus, or storage mites occurred in mattress dust samples from 23 of the 65 homes, and in 10 homes more than 100 HDM/g of mattress dust were found. Mites were more prevalent in mattress dust from the basement and ground levels than from the upper floors. Sensitization to HDM was strongly with the presence of domestic mites in mattress and floor dust. Previous longer stays in southern Sweden or Europe were also associated with present sensitization to HDM, and this was independent of occurrence of mites in the residence. The results indicate that HDM growth and potential for sensitization in cold, temperate regions is highly dependent on the microhabitat, and that sensitization to HDM should be possible to prevent in such climatic regions.