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- Material and methods
The background of this study is the finding of several studies that the frequency of respiratory allergies was significantly higher in the former West Germany than the former East Germany. The present study investigated the levels of allergens of house-dust mite (Der p 1 and Der f 1), cat (Fel d 1), and cockroach (Bla g 2) in the household dust of 201 homes in Hamburg (West Germany) and 204 homes in Erfurt (East Germany), and examined the factors that affect these levels. The characteristics of homes were assessed by a questionnaire. The allergen levels were studied in dust from living rooms (LR), bedrooms (BR), and mattresses (MA). We detected in samples from Hamburg significantly higher allergen concentrations than in Erfurt: three times higher Der p 1, five times higher Der f 1, and three times higher Fel d 1. For Bla g 2, no comparison was possible because the concentrations were below the detection limit in 93% of the samples. Most of the differences could be explained by differences in housing and living characteristics between both cities. The mean ratio of Der p 1 levels in mattress dust between Hamburg and Erfurt decreased from 4.1 to 1.54 (NS) after adjustment for season, building material, age of the house, story of the dwelling, type of heating, age of carpet/mattress, presence of dogs, and indoor climate (temperature, humidity). The mean ratio of Der f 1 levels decreased from 6.9 to 2.78 (P<0.05) after adjustment for these factors. The mean ratio for Fel d 1 in mattress dust decreased fom 4.03 to 1.65 (P<0.05) after adjustment for season, building material, story of dwelling, size of dwelling, ventilation, cleaning routines, and pets. A similar reduction was seen for floor dust (LR plus BR). Our results indicate that the differences between the concentrations of mite and cat allergens found in Hamburg and Erfurt are explicable mainly, but not completely, by different building characteristics (age of houses, building material, story, and size of the dwelling) which affected the indoor climate, as well as by differences in other individual living habits (keeping of pets, age of carpets or mattresses, and cleaning routines).
In recent years, a continuous increase in IgE-mediated atopic disorders such as hay fever and asthma has been observed worldwide ( 1). The causes of this increase seem to be multifactorial in that genetic and environmental factors work together.
The reunification of Germany offered a unique opportunity to compare the prevalence of atopic diseases between the East and West German populations ( 2–7). All these studies yielded some unexpected results. Although there were much higher levels of ambient sulfur dioxide and total suspended particulates in East Germany, the frequencies of respiratory allergies and specific IgE levels were significantly higher in subjects from West German regions. The reasons for the lower prevalence of atopic sensitization in East Germany are still unknown. The genetic background in both parts is probably similar, and several suggestions regarding different living conditions over the last 40 years are rather speculative ( 8). Many East Germans live in multifamily concrete slab or brick houses in rather small and crowded apartments. Furthermore, the former East German homes were poorly insulated; often the heating could not be controlled in individual apartments; because heating costs were low, occupants controlled the temperature of their apartments by opening windows ( 8). In contrast, in West German homes, high energy costs caused home owners to insulate and seal buildings. Well-insulated, airtight homes are believed to create damp environments that augment the growth of molds, mildews, and mites ( 9).
Recently, Nowak et al. ( 10) observed a higher prevalence of atopic sensitization in Hamburg (West Germany) than in Erfurt (East Germany) and suggested that childhood factors and exposure to indoor allergens and irritants were probably responsible for the differences observed between the two cities. On the basis of these observations, a joint project has been established to investigate the influences of indoor factors and genetics in asthma (INGA) ( 11).
The purpose of this study, as part of the INGA project, was to analyze the concentration of indoor allergens (house-dust mites, cat, and cockroach) in dust from randomly selected homes in Hamburg and Erfurt, respectively. We report on the influence of home conditions on allergen levels in these homes.
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- Material and methods
Many factors may contribute to bronchial hyperreactivity; however, there is evidence that, with increased exposure to house-dust allergen, the risk of sensitization and development of allergic diseases has increased ( 18). While the level of indoor allergens in West German homes has been examined for some years ( 16, 19), allergen exposure in East Germany has only recently been reported for mite allergens ( 20). Understandably, a comparison between levels of allergens of different studies is limited because the dwellings were selected by different criteria, and different sampling methods and laboratory analyses were used. No valid data for comparison of indoor allergen exposure between East and West German homes are available. To our knowledge, this study is the first direct comparison of indoor allergen levels in East and West German homes by the same methods.
Dust samples were collected for more than 1 year to minimize seasonal influences. The data presented here demonstrated a high prevalence of mite and cat allergens, but not of cockroach allergen, in the dust of the homes. Cockroaches are a common source of indoor allergen in some parts of the world, particularly in the homes of subjects of lower socioeconomic status ( 21). The significance of exposure and sensitization to cockroach allergens in Germany is still unknown. We could detect the major cockroach allergen, Bla g 2, in 57 (14%) of the homes investigated. However, the level of cockroach allergen was below the detection limit in 93% of the total samples studied. Pollart et al. ( 22) found up to 50 times more cockroach allergen in house dust from the kitchen floor than in that from the bedroom. But we detected Bla g 2 in only one dust sample from 25 kitchen floors in the pilot study ( 13).
Our results demonstrate that house-dust mites probably occur in most homes at any one time, but with a wide variation in both species and quantities. This is well known from previous studies performed in regions with a temperate climate ( 23). We were unable to detect mite allergens in only 38 homes (9.4%) (11 in Hamburg and 27 in Erfurt). We detected exclusively Der f 1 in 71 homes and in 25 only Der p 1.
A comparison of actual allergen levels with data from earlier studies is difficult because the sampling conditions (homes of atopic or nonatopic subjects, sampling time, sampling location, and sample handling) are different. Lau et al. ( 24) found median Der p 1 and Der f 1 concentrations in mattress dust in Berlin, West Germany, of 0.6 μg/g dust (133 atopics) and 0.4 μg/g dust (55 nonatopics, respectively). Higher Der p 1 (1.35–1.61 μg/g dust) and Der f 1 (2.48–2.93 μg/g dust) concentrations were found on the mattresses in southern Germany ( 16).
In keeping with most previous studies, the quantity of mite allergens was significantly higher on the mattresses than on the floors of bedrooms and living rooms in Hamburg and Erfurt.
An interesting finding was that D. farinae was the major mite species in both cities. Other investigators reported similar findings ( 16, 25, 26). Because D. farinae appears to be less sensitive to humidity loss ( 27), we suppose that the prevalence could be related to long periods of dry weather. The fact that the ratio of Der f 1 to Der p 1 was higher in Hamburg than Erfurt is difficult to explain. A possible influencing factor might be that Hamburg is an important transportation center, and it is not known how long D. farinae can survive in a semiarid environment when imported from mite-prevalent areas. Moyer & Nelson ( 28) examined dust samples from imported furniture and noted the presence of living mites after 2 years. Furthermore, another East German study showed the preponderance of D. farinae in urban homes and D. pteronyssinus in rural homes ( 20).
As stated in the literature, the number of mites in homes is related to humidity, building characteristics, and indoor lifestyle factors ( 29). In our study, a significant association of humidity (relative as well as absolute humidity), temperature, type of heating, story of the dwelling, age of the house, age of carpet or mattress, keeping of dogs, and Der p 1 concentration was obvious ( 15). These factors largely explained the different Der p 1 concentrations in Hamburg and Erfurt homes.
In contrast to Der p 1, the Der f 1 concentration was less affected by room temperature and humidity. However, the association of Der f 1 concentration and story, age of carpet or mattress, and dog explained only partially the difference between the cities. The difference in Der f 1 concentration in homes of both cities suggests that other, unidentified features of homes may have an influence on the dust-mite microenvironment. Our data exhibit both qualitative and quantitative variations in mite allergens in the two cities and may be also attributed to variation in geography and climate, particularly the humidity of the regions, which varies significantly. Erfurt is considered to have lower humidity in the summer, autumn, and winter, while humidity in the coastal region of Hamburg is comparatively higher, a factor which helps house-dust mites to thrive.
Hirsch et al. studied the exposure to mite allergen in East German dwellings in Dresden, Halle, and Aue shortly after the German reunification (1992–6) and assumed that indoor conditions were not specifically disadvantageous for mite growth in East Germany ( 20). This supposition did not apply to Erfurt homes. The higher proportion of homes with central heating systems in Erfurt (71%) than in Dresden (45.8%) probably biased our data on exposure to mite allergen toward lower values.
Needless to say, the highest Fel d 1 levels were found in homes that had cats. The cat allergen Fel d 1 was found in 97.5% of homes, and this is in line with the common view that this allergen is ubiquitous in homes, as demonstrated by other studies. It is attached to wall surfaces ( 30) and can be introduced into the home by the occasional visit of a cat or a cat owner ( 31).
In accordance with other studies ( 31, 32) the concentrations of Fel d 1 were higher in dust from living rooms than in dust from bedrooms, but this was only so in Erfurt, where, presumably, either the cats had no access to the bedroom, or the bedrooms were more often or more efficiently cleaned than the living rooms. Similar levels of Fel d 1 were found on floors and mattresses in homes of Hamburg.
Indoor Fel d 1 levels are influenced by ventilation of the homes, but not by the humidity of the area ( 33), although damp homes have been reported to have higher cat-allergen levels ( 17). We found that different factors (ventilation, size of dwelling, and cleaning routines) influence the Fel d 1 levels in dust, but the most important factor was the cat itself. The size of dwelling, the cleaning routines, and cat presence appeared to be the major factors for the different Fel d 1 levels between Erfurt and Hamburg. The higher content of cat allergen in house dust in Hamburg reflects the fact that there are more cats in West Germany.
To summarize, our results are approximately representative of living conditions in Erfurt (East Germany) and Hamburg (West Germany) in the years 1996–7 with respect to main dwelling characteristics. It was found that the level of mite and cat allergens varies between both areas. The higher allergen levels found in Hamburg than Erfurt were mainly caused by different building characteristics (age of home, building material, story, and size of the dwelling) which influenced in part the indoor climate, and other individual living habits (keeping of pets, age of carpets or mattresses, and cleaning routines). Thus, differing housing conditions persisted even 5–6 years after reunification. Since East Germans more and more accept the western lifestyle, we may expect an increase of the indoor allergen exposure in East German homes. The future will show how long it takes the eastern allergen level to reach the western one.